VIEWS
OF
ASTRONOMY.
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         SEVEN  LECTURES


DELIVERED BEFORE THE MERCANTILE LIBRARY ASSOCIATION OF NEW


    YORK IN THE MONTHS OF JANUARY AND FEBRUARY, 1848.
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V
       J.  P.  NICHOL,  LL.D.

PROFESSOR OF ASTRONOMY IN THE UNIVERSITY OF GLASGOW.
REPORTED FOR THE NEW-YORK TRIBUNE


  BY OLIVER DYER, PHONOGRAPHIC WRITER.
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             NEW-YORK:

GREELEY & McELRATH, TRIBUNE BUILDlNGa


                 1848.
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EWBANK'S   HYDRAULICS   AND   MECHANICS.
                                 OPINIONS OF THE  PRESS.

  This Is a highly valuable production, replete with novelty and interest, and adapted to gratify equally the his
torian, the philosopher, and the mechanician, being the result of a protracted and extensive research amon* thfl
arcana of historical and  scientific literature.  Mr. Ewbank's work can not bo too widely circulated.  It is an
elegant " Table-Book," suitable to all persona—to the  ordinary reader, who is anxious to acquire useful knowl-
edge, as well as to the theoretical and practical connoisseur in hydraulics.  Hundreds of impressive biographi-
cal and historical anecdotes, generally unknown, might be quoted as proofs of the multifarious intelligence  which
Mr. Ewbank has amassed for the edification of those who may  study his richly-entertaining volume. We know
not a compilation  specifically designed to exhibit that mechanical philosophy which appertains to common, do-
mestic, and social life, with the public weal, to which the attention of youth can be directed with equal amuse-
ment and beneficial illumination as  to Mr. Ewbank's  acceptable disquisitious.   Therefore we earnestly recom
mend his volume  to their study in preference  to the perusal of those  fantastic and pernicious  fictions  which
pervert the imagination, and deteriorate the mind, and corrupt the morals of the thoughtless myriads who
"feed on those ashes."—National Intelligencer.
  It throws more  light upon the progress of mankind from the  earliest ages, in the useful arte, than any volume
we  have ever seen.—A lexander's Messenger.
  The only volume ever published embracing an account of all the contrivances employed in different ages by
different people for raising water.   It is really one of the most remarkable publications connected with me-
chanical philosophy that has ever fallen under our observation.—Merchants' Magazine.
  We have long known that Mr. Ewbank was preparing this work for the press, and have looked for its publi-
cation with a conviction that we should derive much valuable information from its perusal; an expectation that
has been fully justified by the result.  His work is not one which can fall still-born from the press, as it is not
one of those ephemeral productions that must sell at the moment or never.—Journal of the Franklin Institute.
  An interesting work of science.  The title will furnish the reader a good general notion of the matter  of the
book, but not of the clearness, method, precision, and ease of the manner of it We believe there is no work
extant which treats of the specific  topics which he has  chosen—none we are certain which describes it with
more fullness of argument and illustration.—Democratic Review.
  All classes, as well the farmer and professional njan aa  the artist and engineer, will rise from a careful peru-
sal of Mr. Ewbank's book wiser and better.— U. S. Monthly Review.
  It contains more valuable, curioua, and interesting information than can be  found in any volume ever pub-
lished on the subject, and is a work which commands the attention, and should be placed upon the shelf, of
every gentleman's library, and in every college and academy.—N. Y. Sun.
  A splendid book. We are inclined to believe that it will be one of the moat curious and interesting works that
have issued from the American press for many years.—N. Y. Tribune.
  It possesses great interest, not only for mechanicians, engineers, and men of science, but for intelligent read-
ers  generally.—Philadelphia Enquirer $ National Gazette.
  A rich mine for exploration by the practical or theoretical  engineer, aa well aa by those who like to make
themselves acquainted with the developments of mechanical ingenuity.—N. Y. Commercial Advertiser.
  This large and beautifully-printed octavo is probably the most valuable volume that the publishers have pre-
sented to the public during the past year.—N. Y. Courier  <$• Enquirer.
  It is a scientific  work, but commends itself not to the  scholar only, but to the mechanic and general reader,
for it is perfectly free from pedantry and learned affectation.—Boston Daily Times.
  An Encyclopedia of mechanics.  It is richly illustrated, full of curioua information, and every way worthy,
by its copious knowledge and its  incentives to curiosity, not only to a place in every gentleman's library, but
what is more, to one on the shelves of every district school library in the state.— Union.
  A thick volume  of nearly 600 pages; but let no  reader be dismayed by its size, for the author aaya with •
good deal of truth, that in the annals of mechanics are to be found incidents as agreeable and exciting in their
nature as anything that can be realized by the imagination.  We  are not sure that a single corner of the  world,
or recess of history, has escaped his laborious researches.—N.  Y. Evening Post.
  Whoever rejects this book from the supposition that it is a dull  detail of machinery and the various applica-
tions of the mechanic powers, will be guilty of great injustice to the author.  It is one of the most entertaining
books we have ever met with, on a scientific subject  It is full  of interesting historical and well-written de-
scriptive matter, interspersed with appropriate quotations from old writers, enough almost to give it the  title of
The Poetry of  Mechanics.—Boston Courier.
  One of the most valuable scientific works which this country has produced.—Albany Advertiser.
  t entitles him (the author) to take rank at once with the very best writers in this department of literature,
\  ether ancient or modern.  Quite as entertaining as Beckman, he exceeds him immeasurably in practical use-
fulness ;  and while aiming, like Ferguson, at a popular style, he brings to hia aid a liveliness  of fancy, depth of
feeling, and eloquence of expression, to which Ferguson was a  stranger.  We have seldom Been  a volume eo
absolutely a ammed with useful information.—London Mechanics' Magazine.
  A compressed library.  On the subject here treated, tomes have been multiplied  to an amazing extent Their
essence is given in this volume.  In short, it is such a work of labor and original research aa we rarely see.  It
is nn acceptable contribution to the literature of mechanical science and practical engineering. It is the kind
of book which every mechanic or inventor ought to consult—London Atheneeum.
  This work is  eminently entitled to be called a history of the human race, since it carries us forward from one
atage of advancing civilization, beginning with the rudest and  most simple efforts  of ingenuity, to the  almost
immeasurably superior wonders of our own day. . . . Whether viewed as a purely philosophical work, or aa a
comprehensive text book for mechanics and inventors, Mr. Ewbank's book is equally valuable. The mass of in-
formation it contains is unusually great, and the immense variety of machines which it describee are illustrated
with about 300 engravings.  It is capable of saving infinite trouble and mortification to inventors.... We have
seldom ueen a more instructive and amusing work.—From the  Surveyor, Engineer,  and Architect's Journal.
  This work exhibits the results of reading and research seldom manifested in these days of book-making.. .
 Description, however, unless aa copious as an index, would fail to afford an idea of its extent and  value.—Lon-
 don Literary Gazette.

   IP" The above valuable work is now publishing in EIGHT PARTS, and sold at 25 Cents each.

                                     GREELEY & McELRATH, Tribune Buildings,  Publishers. 
VIEWS
OF
ASTRONOMY.
             SEVEN   LECTURES

DELIVERED BEFORE THE MERCANTILE LIBRARY^ASSOCIATION OFLNEW-YORK
          IN THE MONTHS OF JANTJAF.Y AND FEBRUARY, 1848.
BY
/
        J.   P.  NICHOL,  LL.D.
PROFESSOR OF ASTRONOMY IN THE UNIVERSITY OF GLASGOW.
REPORTED FOR THE NEW-YORK TRIBUNE
  BY OLIVER DYER, PHONOGRAPHIC WRITER.
               NEW-YORK:
GREELEY & McELRATH, TRIBUNE [BUILDINGS.

                    1848. 
 
INTRODUCTORY.
     The following Lecturea were delivered in thia City in the months of January and February of the
 present year.  They were received with the higheat aatisfaction by a crowded  and moat reapectable
 audience, who, at the cloae, passed a unanimoua vote of thanka to their diatinguiahed author.  Having
 been regularly reported verbatim in The Tribune  by that well-known Phonographic Reporter, Mr.
 Oliver Dyer, a very general wiah haa been expressed for their publication in a form more auitable for
 preaervation, in compliance with which the preaent collection of them is laid before the public.
     Thoae into whoae handa they may fall aa the firat apecimena of the glowing and eloquent yet lucid
 manner in which Dr. Nicholl sets forth the sublimeat lawa and grandeatgeneralizationa of Astronomy,
 will naturally desire to  know something of the man who thua brings matters more more eommonly
 locked up in dry, scientific formulaa within the reach of the popular apprehenaion. The life of Dr. N.
 without being marked by any extraordinary incidenta, ia yet deeply intereating aa an illuatration of the
 success with which talent and perseverance can make their way against opposing circumatancea.  Born
 in 1809, in an obscure village in the south  of Scotland, he is indebted solely to hia own efforta forthe poai-
 tion he now holda.  He ia in every way a aelfmade man, and haa the advantage  of a wide practical
 experience in varioua conditionB of life.  Devoted from the first to acientific atudies, he has discharged
 aucceaaively the datiea of a teacher in all the gradea of  that employment.  He haa  now for aome years
 been Profeaaor of Aatronomy in the University of Glaagow, in which 8ituation he haa gained hia present
 elevated general reputation.
     The preaent viait of Dr. Nichol  to thia country ia undertaken in compliance  with a longcheriahecJ
 desire.  He ha8 leave of abaence from hia official dutiea for the period of one year, during which he pro-
 poses to viait our leading citiea, and if hia experience in Boston and New-York be a test, will scarcely
 be allowed  to pasa through any  of them without being called to addresa the public in lectures on hia
 favorite Science.
     Aa a popular speaker Dr. N. is peculiarly gifted.   To an exterior and manner which win the attention
 of his audience, he unites a style of speech at once chaste and impassioned, as eloquent and finished as
 it is rich and glowing.  When treating of the more  magnificent branches of Astronomical Science, his
 periods seem to rise and and roll forth with aomething of the luminoua grandeur which ia characteriatic
 of their aubjecta. There are paaaagea in the following Lecturea, and in others of his productions, which
 are scarcely surpasaed in literature.
    Perhapa the greateat and most permanent di8tinction to which Prof. Nichol  ia entitled ia that of
 rendering the great trutha  connected with  the  atructure of the heavens acceptable to the  public
 at large.  In this he has conferred a greater benefit on the world than could be done by the discovery of
 anew Comet, or the reaolution of any merely theoretical problem.   Until recently these truths were
 a  sealed book save to the learned few; now they are the common  property of all,  expanding the minds,
 elevating the hearts and kindling the  imaginations and the religious sensibilities  of thousands  to whom
 they might else have remained unknown for ever.   It was this which gave to Dr. L ardner's Lectures
 on kindred subjects their extensive and continued popularity.   Prof. N.'s writings have been republished
 in this country, and with the labora of our own Mitchel, who has followed in the  same path, have had
 an extensively beneficial influence.
    Perhaps the best known in America of the worka  of Dr. Nichol is his " Views of the Architecture
of the  Heavens."  This has been very widely read and admired.  It sums up the great discoveries of
Herschel and Laplace in a most worthy and successful manner, and is generally regarded by its readers 
1\
INTRODUCTORY.
 as a sublime and even an overwhelming book.  Indeed, we know of no work of its sizs which presents
 such a mass of stupendous facts and principles.  It carries the reader into the inconceivable domains of
 infinite space, where the thick universes are sown like dust in the sunbeam, and humbles while  it ex-
 cites the mind with the grandest displays of Omnipotent Wisdom and Power.
    We believe that the readera of these Lectures will find in them abundant evidence of the same
 brilliant genius; at least  such confidence is justified by the testimony of all who heard them delivered.
 We annex a list of the published works of Dr. Nichol :

    I.." Views of the  Architecture of the  Heavens."   II..Contemplations   of the Solar  System.
 III..Thoughts on Important Points connected with the System  of the World.     IV-.On the Planet
 Neptune.    V.-On the Stellar Universe.    VI.. A Treatise with Preliminary Description and Notice
■of"Willson on the Education of the People." 
ASTRONOMY.
                                      LECTURE  I.

Means of Penetrating'into Space, and Examining Remote Objects.... Estimate of the Powers of the Telescope....
   General  Aspect of the Starry Heavens....Questions a* to the Significance and Ex ent of onr Vast Firmament
   ....The Milky Way....Limits of our Great System....Discovery of External Clusters or Masses of stars,each of
   which is to the individuals composing it, their own peculiar heavens... .Extent and Magnificence of the Material
   Creation—Its Infinite Variety....Concluding Reflections.
  This distinguished  Astronomer was greeted on
the evening of January 25 by a large and highly
intelligent audience, who manifested the  deepest
interest throughout hia Lecture.  He apoke as fol-
lows :
  Ladies and Gentlemen: Already 1 have learned
enough of America to know how needless  it is
that sfvisiter from Great Britain ahould begin an
intercourse such aa I propoae to establish here with
any thing merely apologetic, for I believe that, theae
two nationa reating on the opposite aidea of'the At-
lantic, in whatever discussion of minor interests we
may be aevered, we are still neither of us inclined
to  forego the privilege  derived from our common
language, and  also a common, and surely I may
say  an illustrious ancestry, of union in the grand
task of exploring  through the mazes of creation
the  mighty ordinances of  God,  and  of  contem-
plating  together,  for a  moment, the deeds  of
those who  have striven to  unfold  them.   Con-
fident, then,  of an  entirely kindly  reception—
confident that I may almost drop  the name of a
atranger, I would now venture  to bring before you
aome of  thoae contemplations  which are  pressed
upon us by a consideration of the lawa which gov-
ern the great Universe in which we are.  I would
venture that we oast  our eyea for a while  upward
from the Earth, toward that dazzling array ot'atara
which, burating forth aa the luminary of  day de-
clines, summons us to the contemplation of those
vast infinitudes in which they are.
  It is my wish, during the present Lecture, to pass
with you upward  from these confines of our Solar
System, toward that grand congeries of orbs of which
our Son is the center, and to trace among  these, if
we  can,  marks of that order and  syatem which
indicate to ua, aadoallthephenomenaaroundus, that
we are here amid  an  Intelligence which preaervea
them even aa at first created It ianot certainly un-
natural  when one  considera the deptba at which
these stars lie, the impassable characterofthegulfs
which separate them from oar Earth, that even at
the threshold of the inquiry, we should be met by
an  unbelief in many respecta, whether or not we
can  reach them, or, at all events, be able to csrry
there a precision of view, without which no perma-
nence of understanding regarding their arrange-
menta  can well be diacerned.  On which account
permit me, in the first place, briefly to place before
you the principle on which these great instruments
have obtained  the power to which we owe our
knowledge of theae  remote realma of Space.  I
would for one  moment, ladies  and gentlemen, pre-
vioua to entering upon the subject, request your
attention to the character of that great  telescopic
power which has enabled us to pierce beyond tbe
confines of our own system, and  examine  those
mighty orbs which fill the boundleaa realma of Space
bey ond it.  The telescope ia not a aimple inatrument -r
but when we look at it with regard to its more sim-
ple elements we see  at once, and clearly, how it
enables us to go into these great profundities. We
find  that when one views with  the naked eye  a
distant object, the power of vision is dependent on
one  plain and  very diatinct circumstance.  It is
thia.   We find that the power of vision  cannot be
made sensible, unless  the light  that comes to the
eye from the object viewed is of a certain distinct
quantity or density.  There can be  little  doubt
that, however far away the brilliant object is, if it
is sending forth light  through all space, that light
must reach every nerve which ia capable of receiv-
ing it; but still, unlesa it reachea the human eye
with  a  aullicient power, density or intenaity,  it
will  not enable that eye to  have the aenaation of
sight or vision.
  Suppoae, for instance, we  have a brilliant point
A, aa thua:      a         b          c
sending out light through all Space; wherever an
eye is placed capable of receiving light from that
brilliant point, it must inevitably receive rays from
that  point; in other words, it must be acted upon*
by that point ao aa to receive the aenaation of viaion.
It ia ao with regard to the human eye.   Unless a
certain density of light  enters it, the sensation of'
vision will not be  preserved.  Notwithstanding-
what the distance of the object may be,  light must-
enter into the eye from that  object.  Suppose, for*
instance, the eye is placed at C: the light coming
from the object A. being dispersed through apace;
will  necesaarily be leaa than the light  at B, and,.
while the light at B ia a definite, diatinct quantity,.
the  light received  by an eye at  C may  not be-
at all  sufficient to  operate   upon  the nerve,
so as to cause the perception of vision.   Now then,.
supposing that when the eye at C is presented to the
brilliant point A, that that point is merely sending;-;
forth a quantity of light sufficient to cause the aen-
aation of light and nothing more, what  would we
require to do in order to make thia point or atar
brighter than it naturally ia 7 It aeetna  to me we
would require to make the light coming  from this)
atar  more dense than it appears to be  when in its
natural atate.  Now, the point ia, how can this be
done?  How can we, by means of any art  or  sci-
ence, place the eye in such a relation to  the star,
that  it shall view a greater quantity of light than it 
■■"5
Prof. Niclwl's  Lectures.
  aafcarally does 7 There is a principle in optics which
  somes to  our aid, of  a  very plain and distinct
  kind, and which I think the audience will et once
  smderstand.  Suppose that we place at B a lens, a
    fieoe of glass so  shaped that  when the rays of
    ghtpass  from the star or  the  brilliant object A,
 'through it,  they  shall no  longer preserve their
 ■ lectitfuear course, butshall be caused by the  lens
  ia cflcverge and fall upon the eye at C.  The au-
  dience will at one perceive that  the  eye at C is
  altogether in a new position.  Instead of receiving
  mezcly a faint, dim ray of  light, it is now receiving
 <«. great, clear and strong ray  of light, formed  by
  $he concentration  by the lens  cf the  numerous
  rays of light, which  previously  were  diffused
  twer a large surface.   Thia is the   principle
  apoa  which  the telescope acts.  It collects the
  scattered raye  of  light, and cause8  them to  fall
  *ap©n the eye in the manner of the lena, as just des-
  ■crifeed.  Let us see, then, what muat be the power
 ■of the telescope, a8 compared with that of the eye.
  It is simply thia: If we have placed between the
 ■«ye  and an external object, any great lena, we
  will flee that object with an amount of light, just
 ;».s much greater aa the lens through which we  are
  ^viewing it is greater  than  the pupil of  the eye.
 "Now, it seems to me that, if we understand this
  very simple principle,  the great power of the tele-
 scope can be easily and at once ascertained.  Sup-
  pose,   then,  we  refer back  to the telescope of
 Galileo—that little, simple telescope with  which
  he first attempted to make his way in the hea-
  vests.   We find that it ia but a little more than
  an inch in diameter.   Yet still, when we com-
  Tsre the aurfaco of light which  that inch neces-
  sarily met, wi;h the quantity of light falling from
 «.ny object upon the pupil  of our eye,  one cannot at
 oil marvel that we ahould be able to 8ee through
  comparatively small  glasses,  objects situated  at
  great distances with very remarkable distinctness.
    Until comparatively  recently, the telescope had
 -mot at all reached the great power which it now
  possesses.   The instrument  recently  used  by
 . at, was perhaps one whose object glass, or  mir-
  ror, was not larger than eighteen inches  in  di-
  ameter.  This was the one  by which Sir Wil-
  tiatn Herachel was enabled to make his  grand
 ■discoveries.   Recently, however, we have  con-
 structed instruments of much greater power.   The
  vast teteacopea of  Lord Rosae have reached the |
 diameter of four and  even  six feet.   Now, if the
 .<3t«<!ience will for a moment consider  the immense
 --s&rf&ce of a  mirror of six  feet in  diameter, com-
 i ^ssred with the surface of the pupil of the  eye,
 ' 1 Chink that it will  not bo at  all marvellous
' "to them that tbe power  of  these  telescopes
-should  be  ao  enormoua  aa  haa  been  report-
  ed.   The  teleseooea  of  Herachel,  which were
- 3.ketit eighteen inches in diameter, posseased nine-
•■  ty-£ve Eimea greater  power of  penetrating  into
-• Space than the  naked eye; but the  power of the
 -dteteacope of Lord Rosse—the greatest one that haa
 recently been introduced—seems to  be something
  '.ess than five hundred time* that of the naked eye.
 ~No»r, this immense space-penetrating power may
« ie approximately realized, by referring for a mo-
 jacat to the great velocity with which light passes
 • Jferosgh space,  which is  about 200.000 miles per
 ■■ second. Now, it seems that Lord Rosse's telescope
  'its tbe power of penetrating through space so  far
 tJSfoat the most distant star  which  it can reach is at
 iSseefa a vast distance from  us, that its  light, moving
 'with this almost inconceivable  velocity, cannot
 Teach us in less than 60.000 years.
    €t is not,  however, merely in regard to their
 ^ewers as light graspers, that the efficacy of these
 :3&a!essopes  mainly depend.   Let this  power  be
 ever so great, little advantage is gained  unless
 there be perfect accuracy of image.   The great ad-
 vantage of Lord Rosse's telescope depends not sole
 ly upon  its power  of penetrating into Space, but
 also upon the accuracy with which it gives us the
 image of the object viewed  through it.  It  is in
 these  respects that that mighty instrument  has
 achieved its greatest exploits.   When the greatest
 magnifying  power  is  applied,  it shows  not the
 slightest amount of distortion in tbe object.  It is
 not possible  to render the astonishing accuracy of
 Lord Rosse's telescope fully palpable.  There is a
 minute point near Polinarius, so minute that it re-
 quirea a good teleacope at  all to discern  it.  Now,
 with  the  very high magnifying power of Lord
 Roaae'a teleacope, I have aeen that point, aa clear, an
 distinct aa a atar of the first magnitude. With such
 powers in our posaeaaion, then, letua proceed rever-
 entially, but still without dread, to scan those truths
 to which they have enabled us to ascend.   When
 regarding the constitution of the Stellar Heavens,
 it is not unlikely that again wo may be stopped by
 incredulity.  According to  our  usual  ideas, these
 starry  heavena seem infinite.   They appear as if
 they occupy all Space, filling with crowds of  con-
 atellationB wherever the human  mind can fancy
that Space ia open to receive them ; and, therefore,
it would aeem that although our augmenting teles-
copic power might bring us augmented knowledge,
 we are yet contending with what ia hopeless. Now,
 as the removal of  this  popular  fallacy lies  at  the
root of all our modern views of the structure of the
heavena, 1 muat 8olicit for it your attention.
  Even after we have aacertained how far the tel-
eacope is able to pierce, it may yet come back to
us as a cause of doubtfulness, whether we can get
a rational conception of how the Stellar Heavens
are constituted. Is it not likely  that these heavens
which we see around ua and over U8,  penetrating
infinitely into apace,  preaent to the  eye nothing
different from what  we aee here?  Suppose  this
question occura to us, ahall we be able to ascertain
aught  concerning  the structure  of  theae great
heaven8 7  Now it seems to ua  at first, perhaps,
that this is a perfectly legitimate objection  to  our
moving farther with our inquiry.   It may be said,
that when we observe the skies  on a clear night,
we have before us all that can be seen.  Now this
graud conception, namely, that if we were passing
throughout space we should simply meet nothing
else than what we see  around  ua—juat  conatella-
tion  after  constellation as  we  went  onward
through  these depths of infinitude—I say  that
this conception is so very natural that it is difficult
 for us to conceive that it is not true.   However, on
 a slight consideration I think that wo will be able to
 aee that thia ia not what our heavena really indicate
 to U8.  If what I aaid were true—if tbe stars ex-
 tend on through our skies  toward infinitude, if as
 we went along—supposing we had it in our power
—throughout these  clusters we should see nothing
 but constellations after conatellatioqa, I think that
 our heavens  would  not appear to us as they do
 now.   Suppose for  instance we  had reached far
 away beyond these constellations what would we
 see behind us 7 We would see the great, brilliant
 stars of the firat magnitude, then we would see
 behind these, those of the second magnitude, be-
 hiud these again those of the third magnitude and
 ao on; but we would find always ia every  part of
 our sky when we reached that  position where we
 could see no more  stars, a sort of background—a
 dim  diffused light called  nebulous Ha lit.   If that
 were the constitution  of our skies this would be
 their appearance.    You would  find lying back-
 ward  through  the   whole path  of the  sky  this
 dim milky light.  On  tbe contrary, we see it only 
Astron
on one side of the heavens  in that great range
called  the Milky  Way.   Now the queation ia,
what is the cause of thia 7   Why do we find thia
great milky  belt, ao  to  apeak,  paaaing over our
■ky in one direction and  not in another?  ltaeema
to me that if we  look  at this queation  calmly
thia  conclusion must neceaaarily occur to ua, name-
ly :^that in that part of the aky alone, where we
aee the Milky Way ia there a bed of stars diffused
throughout the unfathomable depths of space.  If it
were otherwise, if this bed of'stars  was found  to
be diffused throughout all regions  of the heavena,
then, certainly, that peculiar appearance that atikes
us as  we look at the Milky Way would be found
aa the background of all the heavena.  In every
range  we would aee the atara of tbe first, second,
third and fourth magnitudea; then, when we arrived
at that part of the heavena where we could not dis-
tinctly trace the individual atara, we would find a,
background filled with thia dim, milky light.
   It seems then that  our first notion, namely, that
these Btara atretch away throughout apace  ia not a
true one—that thia Milky Way manifests to  us a
peculiar structure.  Now the que8tion  ia, what ia
that structure 7 how can we ascertain what that
Structure ia 7   Belonging to the  great bed of atara
in the midat of which we are. we find, on looking
at the heavena, that atara of the first,  second and
third magnitude are tolerably  equally scattered
throughout all apace. It ia only  when we come to
stara of the very 8malleat magnitude that we find
-a derangement of thia diatribution.   Whatdoea thia
indicate to us 7  It aeema to indicate the following,
namely: that aa far aa the naked eye can reacb, theae
stara, on to the very smalleat magnitude, are pretty
equally acattered throughout our akies ; but that if
we get beyond their region, peculiarities of consti-
tution come into view, and we begin diatinctly to
see  that we do not belong to a universal, but to a
certain, definite and distinct class or mass of orbs
with which we are counected—a masa  of orba with
boundariea almost inconceivable, but still a definite
-and distinct mass.
   The  idea  that I have thrown out may yet  be
puahed a little farther.   It  may  be shown that if
theae atara were  diffuaed through all apace, our
heavena would on every aide blaze with a splendor
so bright  that the Sun would not  be viaible to us
at noonday.   It ia clear, then, that auch canuot be
the  characteriatic of our akies.  It cannot be that
theae orba we are discerning are apread infinitely
throughout spane, bat, on the contrary,  in all likeli-
hood thev are forming a great cluster or bed of stars
of a peculiar  and distinct shape.   These thoughts
which I have  just  laid before you were first seized
by the illuatrioua Sir William  Herachel, and  al-
though hia concluaions cannot be placed before you
aa infallible, yet hia first ideaa lead us in our firat
progress toward a view of the heavens. Herachel'a
first conception with  reference to the nature of the
heavens was the following.  He aaid,;' It ia clear
that thia great multitude of fixed atara ia not what
it waa formerly suppoaed—the infinite  heavena.—
Thia great masa of atara ia aimply a vaat cluater or
congeriea, and nothing  more."  When thia great
idea had dawned upon him, he asked, " Ia it poaai-
bleto aacertain what ia the deacription,the general
character, of that vaat bed of orba  in the midat of
which we are 7"  The notion waa certainly a very
great and marveloua one, but still he waa enabled
to come to a concluaion not very far, I believe, from
what w« now think to be tbe true one.  The idea
upon which  he worked waa the following:  He
■aid, " Suppoae that thia room ia filled with peraons,
and  that they are pretty equally diaperaed over it.
Now auppoae that I turn my eyes in a certain  di-
rection and count the  number of persons that I see
\omy.                                  '     '

before me, and then direct my eyes to another partof
the room and again count the number of individuals
that meet my gaze: then, being certain that these
persons were pretty equally acattered throughout the
room, I would be enabled to infer from the number
of peraona located in the aectiona of the room  to
which I had directed my inveatigationa, how far I
muat be from the edge of the room in thia or that
direction." Thia was Herachel'tf idea, and he turned
hia great telescope in every direction round the
heavens, judging how many stars he saw in  every
place, and he found in thia manner how far he sup-
posed he waa from every portion of the edge of the
cluater.  The mode in which he attempted to make
out a scheme of the character of the heavens was this.
   [The lecturer  here  drew  a diagram upon the
black-board reaembling aluminoua body from which
ray a of light emanated in every direction—the rays
varying in extent in such a manner as to form a
sort of elongated spheroid indented at the edges.]
   Suppose this (pointing to the luminous body) is
the Sun, and these lines (pointing to the rays) indi-
cate  the  directions  in which hia telescope was
 turned, and their lengths indicate  the  number  of
 atara he obaerved.  Well,  he turned hia teleacope
 all round through our heavena and drawing a aketch
of thia kind,  he then joined  the edgea of theae dif-
 ferent linea, making a figure like thia.  And he said
 " this, in  all likelihood, is something of the  shape
 of the great  cluster  of stars in  which we are."—
 His idea, perhaps, is better represented thus. Let
 the audience in imagination follow me.  Suppose
 we bad it in our  power to move  up through the
 Milky Way and pass  along through that congeries
 of stars till we lose our connection with the Siderial
 system.  The  following phenomena would  be ob-
 served : We should paaa on from our preaent con-
 geriea, still moving,  aa it  were, amid an infinite
 number of orba, till, by-and-by, we ahould have no
 stars  in advance of ua and the only systems  would
 be behind ua.  Suppose we ahould go  still farther
 out amid theae awful receases till thia vaat scheme
 of oura would take on gradually  and gradually the
 shape of a mere apeck lying against the dim of the
 far heavens.  Such would  be the general aspect of
 that masa of stara with which we are in immediate
 connection.  [Applause.]
   The inveatigation which  led Herachel to the con-
 ception that thia  waa the  acheme of our heavens,
 was the following—and jou will perceive at once
 that it was subject to two great errora:  On trying
 to find out a view of the sfeiea, he bad the concep-
 tion  conatantly in his mind, that the atars were
 pretty equally  scattered through all space.  Now,
 to return to  my illustration : auppoae that I were
 to  count the  persons in, different  directions
 around the room, and inferring  from that how  far
 I was from  all aides of the room, I  would  neces-
 sarily rest  upon tbe  conviction that  the people
 were equally scattered throughout the room.   So
 Herachel said that the great mass of stara through-
 out the heavena were pretty equally  diatributed.
 Now, since  hia time  it haa been aacertained that
 thia ia not true.  It haa been found that all around
 us, so far from the Btara being pretty equally scat-
 tered, they are, quite on tbe contrary, thin, aa if in
 a desert.  Herachel waa,  therefore, wrong in his
 opinion of the  scattered  condition  of the orbs
 around us.   There was another thing in which  he
 was erroneous.  You will observe that when look-
 ing all around in the aky, he could never have sup-
 posed that he was entitled to draw the conclusion
 with respect to the depths  of the orbs in any direc-
 tion, unlesa he knew, or had reaaon to believe, that
 his telescope enabled  him to go to tbe end, or at
 least nearly to the end, of our system in that direc-
 tion.  Suppose, again, that I was here counting tho 
8
Prof. NicJwl's  Lectures.
number of persons that I see in any direction—un-
less I was sure that I had arrived at the end of the
room, it is plain that  my counting  would be of no
value as far as certainty is  concerned.  This was
also another of Herschel's views, the inaccuracy of
which has been fully proved.   He found,  and we
find now, that not the largest telescope has ever
been able to pierce to the extremity of our system.
Perhaps the best inference we can draw is the fol-
lowing : We are not speaking of the  Solar System,
but of that vaat system of orbs that you see on a
clear  night beaming across the  heaveBS.  Well
then,  the  question as to what our  System  is. is
probably better explained by our looking at exter-
nal objects than it can be by oar viewing the aspect
of what lies quite within it. For instance, this is
one immense cluster lying perfectly apart from our
System.
   [The lecturer here  pointed to a  chart, on which
waa represented  a brilliant cluster of stars com-
 osed of three rings, one within the other, the moat
 rilliant being in the  center.]
   We find this when the posver of the telescope Is
fully applied, to present an  appearance like that on
the chart.   How far this cluster is removed fromus,
it is utterly impossible to tell. Its appearance, how-
ever ia not very  unlike what  that of our  system
might be, if it were viewedfrom this distance. If we
consider for a moment this  statement, it will not
appear improbable.   The  milky-way is a  great
ring extending in two ranges through our heavens,
so that it may be that our system is an  immense
riBg similar to thia cluster.  If this idea is realized
another immediately suggests itself, and  which
Herschel  also early recognized.  Vast as  our fir-
mament may be, has it boundaries, or does it stretch
away into infinitude7  Are those awful spaces that
surround it on every side void, empty, or  are they
tenanted  by worlds and systems similar  to our
own?  No  wonder that a mind  like Herschell's
should have rushed to the conclusion that the space
around our system was a vault in whose capacious
bosom myriads of mighty  clusters  like our own
universe are placed.  If it  be true that this great
scheme of ours is simply that which Herschell first
supposed  it,  but still a great, separate, distinct
scheme, whose nature ia, perhaps, more than any-
thing else, represented by these singular Nebulae,
what must we think with regard to it 7   Surely it
is that, notwithstanding its immense diffusion, its
vast confines, the great space through  which  its
different portions range, there must lie around  it
on every side, vast untenanted spaces,  and  if this
be so may it not be that amid  all  that space also,
there are floating great schemes of being like ours,
schemes I say of different  shape,  of different char-
acter, but lying in these vast regions of space like
ours, schemes quite as magnificent as that vast
system to which we ouraelves belong.  If this is so
what a  conception in regard  to the material
universe, must press itself upon our  notice.
   It  seems to me the conception must be juat like
that which a dweller upon an island in the great
Southern  Ocean, who had never passed beyond the
limits of the little world in which he lived would
experience, if to him were brought information thaj;
what he conaidered his world was but a diminutive
island, and that around him in this Ocean lay scat-
tered large groups of islands and vast continents-
Such is the information with respect to the  Stellar
Universe that has been conveyed to us by the pow-
ers of our great telescopes. [ A pplause.j
   The great inquiry ia this: What  is the character
of these immense groups ;  what their form  ; what
the  nature of the shapes in which we find them
collected;  and what the destiny through which they
are doomed to pass 7 Now  in the first place we fiod
that these groups are for the most part approaching
to circular—I should hardly uae the word circular,
but spherical. Now that this ia not altogether true ;
that we do not find them altogether spherical may
possibly be repreaented to you by merely looking
atone masa of theae elementa.  [The lecturer here
exhibited another diagram, repreaenting a nebu-
loua group, of a nearly  circular form.]  Thia mass
ia aomething like what by far the greateat num-
ber of  theae different groups are; but when our
greatest  telescopes are brought to  bear to upon
them, we find that those which which were thought
to be spherical are not so; thoy approach nearer
to a  globe.  Here is one  which looked oval, but
Lord Ross'a telescope  brought it  into a  circle.—
Lord Rosa called it the  crab nebula,  because it re-
sembles a crab.
  Now, there occurs a very remarkable circum-
stance  in reference to thesecomparalively sweep-
ing circular maasea of nebula*.  We find they are
not entirely  circular,  but the reverae,  and that all
around them, on every aide, there are volumes of
stars stretching out  apparently  as  if they were
rushing toward a great central maaa in conaequence
of the  action of some great power—tbe power of
gravitation.  We find them approaching to spheres,
and around  their spheres we find these volumes
apparently  tending toward a center, which ulti-
mately may become the great central region.
   If  this  ia true—if  the  idea is correct] that
great masses auch as  this, for instance, are in the
mean time merely in a condition  of change—that
all these orbs are now forming their volumes with
a view to become ultimately incorporated with it—
how stupendous the idea!  It takes  our thoughts
from the mere transitories of Earth, and  places
them on the august things of Eternity—it realizes,
as closely as the material Universe can do to Man,
the awful unchangeableness of that Being who has
created  these things,  whose ateps  fill Eternity.—
Passing from these  remarkable spherical masses,
on toward the irregular ones, we find that, although
we cannot  at all understand them  as unities, yet
there  are  clear and  distinct manifestations  of
changes passing along them so great that we  are
obliged  to  look upon  these changes as containing
the secret of the remarkably capricious forms these
orbs have.   Suppose,  for instance,  we  look upon
I this circular mass [pointing to a diagram] so far
 away that light cannot come  to  us from it in
 less than  sixty thousand (60,000) years.  If we
 look at this, it will be seen that it is almost im-
 possible to  reconcile  its curious form  with  any
 shape.
   Now, although we find  it inexplicable when we
 look at it as a unit, yet when we examine its differ-
  ent parts we will see  that there may have been—
  that there are proceeding there great processes
  which will ultimately  have such an effect upon that
  singular mass  of orbs as to turn it into a different
  position from  what it now  occupies,  There is
  something very remarkable  in the forms of these
  nebu'ai.   The  audience may have looked  with
  some attention to the Milky Way.  If so they will
  have  seen that it is not at all like a regular, dis-
  tinct  belt,  of brilliancy, from which we could infer
  that  there  is  a regular succession of great  orbs
  stretching out behind it.  Instead of being a  regu-
  lar belt it  seems  like a succession of groups or
  masses of stars, precisely like what we see repre-
  sented  in the diagram.  Its appearance is so very
  remarkable that Sir Wm. Herschel  aaid when he
  first saw it, tbat " it was breaking up, and that the
  intervala  of  space  lying  between  the bright
  parts are like  tbe  wrinkles of  age  "  He said
! tbat  "after a lapse of ages this vast belt would
J disappear—that instead ol  being  a separate dia- 
Astronomy.
tinct  belt, it would be  a  mere  succession  of
brilliant, separate orbs or clusters  stretching out
through the whole heavens, but perfectly distinct
and aeparate."  He even went bo far aa to aay, in
one of hia great mooda,  that " thia great break-
ing up of the Milky Way looked to him like the
movementa of the vaat Chronometera of the Uni-
verae; that there were paaaing onward the distinct
movements of the mighty Hand which marks the
progression of the material Univerae." To specula-
tions like these one can add  no adequate illustra-
tion.  They are clearly beyond any aphere to which
our human machinery can ascend.
  The proceas of change in these nebute being
probably  beyond the existence of  the individual
and the duration of the human race, the character
of that change can never  be evolved except by a
close comparison of all the forms which it involves,
which will engage the energies of all the observa-
tories  of the  earth.   Thia comparison muat not  be
undertaken even for the gratification of an enlight-
ened curiosity, but  for the purpoae  of elucidating
one of the greateat  questions that  ever  occupied
the attention of  man.  In thia  investigation your
own great telescopes at Cambridge at Cincinnati
and other places must asaiat, not, aa I aaid before,
for the gratification of curioaity, but with  the view
of having mapped  down  the8e great  nebuloua
changea, that we may get at the law which gov-
erna the movementa of theae wondroua bodies.
A Ladies and gentlemen: I have endeavored to give
you some idea of the nature of the gorgeous Uni-
verse amid which every moment of our existence
is passed.  How strange that this Universe is only
yet cognizable by one human sense! that the veil
of the Sun's light entirely conceals its wonders from
our view—that had the light of that Sun  not been
veiled by the curtain of  night we had lived amid it
and never have known of the existence of the
Stellar Universe.  May it not then be true that dur-
ing midnight, when theae infinite orba appear to us
from their unmeasured depths—may it not be true
that through veils as thin we are withheld now from
the consciousness of other Universes vast even as
the world of stars!  But in reference to an idea so
lofty, let me use the language of a greatmind:

   Mysterious Night! when our first parent knew
   Thee by report divine, and heard thy name,
   Did he not tremble for thia lovely frame,
   Tnis glorious canopy of light and blue?
   Yet 'neath a curtain of  translucent dew
   Bathed in the rays of the great setting flame,
   Hesperus and the hosts of Heaven came,
   And, lo I Creation widened in man's view.
   Who would have thought such darkness lay concealed
   Amid thy rays, 0 Sun I or who could find
   What fly and leaf and Insect had revealed,
   That to such countless orbs thou mad'st us blind ?
   Why do we then shun death with anxious strife ?
   If Light can thus deceive, why may Lot Life \

  The Lecturer reaumed his seat amid the general
applause of the audience. 
10
Prof. NichoVs Lectures.
                                      LECTURE  II.


The Mechanism of these grand Stellar Clusters....Our Heavens replete with Activity and Motion....The System of
   Double Stars....More complex Groups.. ..idea of a Universal Mechanism... .The Motion of our San through
   Space.... Idea of a Central Sun---Tbe instability even of our grandest forms and cellocationa of Matter. ...Rela-
   tion of Material Changes to the Will of God.
  Ladies and Gentlemen : I endeavored to ex-
plain in my last  Lecture what lights have now
reached  us respecting  the arrangement of the
Stellar Univerae.  Upon examination we find that
the  brilliant orbs which  compose this vast  Uni-
verae, are  not  diatributed  with  any  apparent
regularity through space, but  are thrown together
into single groups or clusters, a few of which have
been analyzed  by the  telescope.  The forms  of
some of theae groups, aa unfolded by the power of
those  mighty instruments,  are  certainly  most
strange, and, whether the inference be correct or
not, they forcibly impress upon ua tbe idea that we
are  looking at incompleteneas—at a  phenomenon
whose entire completeness is  not displayed in its
existing form—which, in fact, belongs to some wide
acheme, and which ia  not intelligible except aa an
intermediate step in the course  of some great pro-
gression.
  I attempted, in my previous Lecture, to lay before
the audience those great lights which we have ob-
tained with regard to tbe structure of our great
Stellar Heavens—to show that instead of the Stars
being diatributed throughoutall apace, our Heavena
are but a simple cluster, a group,—a limited, defi-
nite and peculiarly shaped group.   The nearest
approach to the shape of thia  group may be found
in the diagram  before  you.   [Here the lecturer
pointed to a large diagram repreaenting an im-
mense spherical cluster of stars, with the sun  in
the center,—the stars as  they receded from the son
growing  more and more irregular in their distri-
bution.]
  in connection with this cluater, the telescope has
shown us a vast variety of others, whose forma are,
likewise, so very capricious  and irregular,  that
when we look at them, we feel the conviction  that
we are looking at something incomplete, unfinish-
ed—that these nebula? are in a  stage of progreaa,
and that they are not explicable aa  the finiahed
produrt of any known law. If my idea ia correct,
—and, certainly, so far as 1 have exposed  it there
is nothing in favor of it except a  probability—we
shall find, by an examination of oar own Stellar
Heavens, proof on every side and in every appre-
ciable form,  that their characteristic is action and
not repose.  That portion of the subject which con.
ducted to the most satisfactory results, was lead in
by an ingenious Englishman named Mitchell, during
the last century, while making observations on the
group of the Pleiades.  On taking a survey of the
heavens, his attention was much attracted  by thia
peculiar cluater, and after bestowing upon it a moat
searching examination, he said, " it is impossible
that this group  of so many  stars,  occupying  so
small a space, can be accidental.  It must indi-
cate system." He even went  so far as to throw
out what, at that time, was a  most bold conjec-
ture,  via:  that  these orbs would manifest  their
connection in a  systematic manner  by  develop-
ing internal  motion.  Unfortunately, however,  in
his  time astronomical instruments had  not  been
brought to such  a state  of perfection  as would
enable this conjecture  to be verified.  His ideas
did not lead to any definite result; nor could they
as science then existed.   But they were subse"
quently revived with great energy  by Herschel*
under auspices much more favorable.  Herschel,
however, did not know that Mitchell had preceded
him in this department.  His attention was directed
to certain peculiar bodies found in  the heavens.
which we now call double  stars, and which, to the
naked eye,  appear just like  single  stars.  But
when the telescopic power is applied to them, they
are found to be two stars  placed  so near together
that the naked eye cannot appreciate the interval
between them.  Previous  to  Herschel's  time it
was known that these stars existed  in the heav-
ens, but they had never been  subjected to an ex-
amination sufficiently accurate to enable Astrono-
mers to determine their constitution and the lawsv
which guide their motions.  It was  not supposed
that they were  s9  near each  other  as they have
since been ascertained to be.  I will illustrate this
point  in the following manner:  Suppose 1 look at
these two lights from such a  direction that they
shall be in nearly tbe same  line of viaion.  If I did
not know  that this large  space existed between
them, I would suppose, from their appearance, that
they lay in  the  same  immediate neighborhood.
Here you will observe was  the difficulty attending
the solution  previous to Herschel's time, of the
problem of the double  stars.  Bat he discovered
that they were  in  immediate  proximity, and  not
apparent merely, as had formerly been supposed.
  Herschel was attracted to this peculiar class of
bodies,  with reference to tbe problem called the
■problem of the parallax, and  his telescope soon
enabled him to discover that there were many more
such stars than could be explained on the old hypo-
thesis.
 ■  I think the audience will
                     be enabled readily to appre-
                     hend the solution  of this
                     problem by Herschel, with
                     the  aid of the diagram.—
                     Suppose our Sun to be lo-
                     cated here  in  the  center,
                     tbe  first  circle to  inclose
                     stars of the first magnitude,
                     and  the second circle to in-
                     close stars of  the  second
magnitude.  It will be seen that it may be calcu-
lated  upon the hypothesis that the stars  are dis-
tributed in a random or average manner through the
heavens, how many of such mere optical combina-
tions might be formed within those spheres; and
Herschel diacovered that the number actually exist-
ing ao immensely exceeded the number which thus
might be produced  that a new explanation was ne-
cessary, and, in Bhort, that the bodies must be physi-
cally and not merely optically or apparently connect-
ed.  Like Mitchell, too, he ventured on the predic-
tion that the reality of this system would be found
manifested by the fact of the bodies rolling around
their common center of gravity in mighty orbits t
and fortunately the  verification was  in this case
not only possible but near.  The examination and 
Astronomy.
H?
 determination  of the periods  and motions of the
 double stars have constituted one of the most bril-
 liant and fertile departments of Astronomy  from
 Herschel's time until now.  This was a phenome-
 non new in science, two grand primary orba being
 found in epecial union and moving through great
 courses.
   Tbe periods of these double stars  exhibit the
 greatest  variety.   Some  are very  long, while
 others  are  comparatively  short.   In  some the
 revolution takes place in fourteen years.  The pe-
 riod of one in the constellation of the Crown is
 forty-three years.   CaBtor, in the conatellation of
 the Twine, haa a period of 215 years, while others
 extend through seven or eight hundred years. We
 have not  been able to follow  these latter through
 more than a small  portion of their orbits; but, a
 small portion of an orbit being ascertained, Geome-
 try enables us to complete the entire orbit, and by
 its aid we have  been  enabled  to  determine the
 periods of these singular bodies.
   1 am very anxious that the audience should re-
 alize the nature of these phenomena.  They do not
 at all resemble the  motions of our planeta round
 their centre, the Sun.  There are, in fact, two orba
 or Suns of the firat magnitude revolving round each
 other, each of which may be  accompanied  by a
 eorteqeof planets aa imposing as those attached to
 our Sun.  Neither the  previous reasoning nor the
 observation which followed it was confined to mere
 Binery groups. The illustrious discoverer went far
 beyond these and traced the same characteristic
 among much more complex systems.  We are now
 aware  of numbers of triple  stars  which  appear
 single to the naked eye, of others that are quadru-
 ple,  and  of aome  yet  higher  combinations.—
 The  moment  Herschel found that some of these
 bodies were triple,  and  discovered still  farther
 combinations,  of  four  Stars, be  was under no
 difficulty  whatsoever  with reference to the in-
 ference he should draw from  these discoveries.—
 He aaid theae groups certainly are physically con-
 nected and will be found to revolve round their
 great centre in correct courae8.  The  motions  and
 periods of some of theae have  alao been ascertain-
 ed. Sometimes we find  the  three Stars moving
 around a common centre ;  at other timea two of the
 Stars are found moving round the third as their cen-
 tre. You must recollect that these are combinations
 of Suns not one of which is inferior to our own great
 luminary.
   Beside theae, we have other combinations of four
 stars.  There is a very beautiful one of thia kind in
 the Conatellation of the Lyre.  When we look at a
 bright star in that constellation, it haa a very pecu-
 liar aspect.  It is not so round and distinct as stara
 usually are.  On applying the teleacope we imme-
 diately  find the cauae of thia strange appearance:
 It turns out to be not one star, but four stars bound
 together,  whose  movementa  are  very extraordi-
 nary.  We find that each two stara  constitute  a
 double star—a system of themselves—and then the
 two syatema  revolvearound a common center.—
 How complex  and extraordinary indeed muat be
 the mechaniam that auataina a System like this.—
 We have  boasted  of our mathematics, of their ac-
 curacy, of their vast and varied powers, but when
 we reflect that it taxea them to  the utmost to fol-
 low the comparatively aimple movements that take
 place within our own Solar System, how useless to
 attempt to apply them to unwind  tbe mechanism
of 8yatema like theae, every one of which is prob-
 ably Burrounded by its own  System of Planeta!—
 (Great applause.)   I should mention, with  reapt-ct
to this fourtbld Syateni in  the  Constellation of the
 Lyre, that the periods  occupied by one of these
Systems cannot be leas than a thousand years, and
the other is about twice that, and the period before?
the whole System returns to its  original  state is*-
not less than a million of years.  But that period.
is small indeed, compared with some that I shal
bring under your notice.
  The  grand fact then is established  beyond  st
doubt, that in so far as we find minor groupa withaa-
our galaxy, we diacern mechanism and change, and
we may venture to apply the same conjecture to still-
greater masses, but  before entering upon  that
grander aubject, there are a few pointa to which I
would invite your attention.  One grand fact  that
haa been elicited by our observations upon these?
double  stars is,  that the law sustaining tiseae
wonderful mechanisma ia the same that austainsoa*
own aystem—the law of gravitation diacovered by
Newton.  Thoae far off suns are moving around be.
their mighty orbits in obedience to that simple law
which causes the apple to fall to the  ground, they
wheel arour.d their common centers  of gravity  ins
precisely  the  same curves in which our plaaetcfr
move.
  There is a curious physical fact also conaectesl'
with these double stara.  Generally speaking, we.
find that the two stara exhibit different colors.  We
find them exhibiting the colors of the two extremes*
of the spectrum commonly called  the complemei*--
tary colors.
  The  audience must be aware  that the  ray  c£
white light which we receive from the Sun is com-
poaed of a number of different colors, which are
blended together in his beam.  In the case of tbe»ar
double stars, however, we find one abining with a
red light, while tbe other  has exclusively a blue
light.  How extraordinary the condition of planet*),
if there be such attached to these variegated Sons*.
now basking under the blended light of both wbieb.'
would constitute a white light, at other times, hav-
ing only a red aun above the horizon, and at others
being illuminated by the blue one.  If one consid-
ers how much of the characters of the liviog fami-
lies on  the earth is dependent on  the action of the-
Sun, it will be  difficult to conceive the endless va-
rieties which muat prevail among  bodies subjected-*
to so singular influences
  Returning, however, to the principal aubjeet, we-
find it to be the character of the minor groups with-
in our galaxy to exhibit a  systematic independ-
ence of their constituents and a consequent mecbsat-
ism and motions.  And now raising our thoughts.'
somewhat higher, looking over the whole  Stellar
Universe,  what are  those  mighty firmaneatav
thoae  gorgeous  systems  lying  apart  in Spaee
except  special groups in regard  of tbe great'
all.  Is it not likely,  then, that  what we have
learned of the minor forms may also characterise
the larger  oneB ?  That juat aa the four-fold group va>
Lyra or aa proudly in the Pleiada, even the multi-
tudes of spherical cluater* or those mere  irreguhwr
ODes are alao united into separate schemes inter-
nally consistent by their own self contained activi-
ties. The question is far too wide  to admit  of a-
deciaive answer, but something of a confirmation
may yet be obtained from what ia elsewhere going-
on around  ua. If the law of tbe minor groupa can be
extended to thoae mightier collocations we ought
evidently to find activity prevailing alao among the
Bingle suns, and as of those  our own orb  is wbat
we know best, this will probably be easiest estab-
lished by observing whether our sun is fixed in one -
portion of space or ia passing onward through some/
great courae.
  The queation that arisea then is thia:  Is oar She
in motion 1 Ia our old idea that the whole planetary
aystem ia  aim ply lying  apart in one nook of space,.
correct; or, on  the contrary, is our sun passing wittc
his  whole attendance of planets through sontfe- 
12
Prof. Nichol's  Lectures.
 mighty career  in the  heavens 1  This latter idea
 baa been long entertained.  It was however to the
 illustrious Herschel—to whom I have had occasion
 80 often to refer—that  we owe the confirmation of
 this great truth.  His  idea was thia, and you will
 aee at once that hia mode of lighting upon the great
 fact was remarkably simple: He said, "If our Sun
 is in motion, how shall  we ascertain the fact ?  We
 ■can not ascertain it by the motion of the Sun him-
 eelf, because we, partaking of his motion, would not
 have it in our power to ascertain that motion inas-
 much as we are going on in the same path.  The
 only mode by which it could be deduced was thia .-
 If the sun were moving through the  heavens,  the
 stars around him  would seem to  be altering their
 position."   Suppose for instance, to illustrate Her-
 echel's idea, that there is a cluster of trees  before
 me and another cluster behind me.  Now if  I were
 to move from  one toward the other,  the cluster
 which I approach would  seem to be opening  up,
 while the cluster from  which I was departing would j
 seem to be undergoing the opposite change—closing i
 £n. Now, Herschel, upon comparing the positions of
 the stars with their positions as laid down in  the old
 catalogues.discovered that justexactly such changes
 were going on among them.  In the direction of the
 constellation Hercules the stars appeared to boopen-
 ing out, while the stars in the oppoaite part of the
 tieavens seemed to be  getting closer to each other.
 Now, said he, " Is not this all I could expect to see if
 the Sun was actually moving through the heavens 1"
 Accordingly he was daring enough  to infer that
 this waa the case and he said our great Sun is mov-
 ing on with all his satelites  toward tbe constella
 tion Hercules.  Again hesaid, "If it be true that the
 Sun is aweeping through apace, then it will be found
 that the atara in allparta of the heavens are  chang-
 ing ; not merely those in the region toward which
 the Sun is  moving and  from which he is departing,
 but sideways  over all the  heavens will distinct
 changes among the stars be  apparent." To illus-
 trate again.  Suppose  for instance tbat I was mov-
 ing through this room. All the objects in it, on either
 side of me. would appear to be moving backward.
 So  has it been  found to be with regard  to the
 whole mass of the stars.  They all present the phe-
 nomena as if they were being passed by the Sun.
 Since Herschel's time these  motions  have been
 scanned with the utmost precision, and his conjec-
 ture has been  most thoroughly confirmed.   There
 •cannot, then, be a doubt tbat our great Sun, carry-
 ing all his planets with him, is aweeping in a
 'mighty cycle through the skies-  (Applause.)
   These general considerations, however, have re-
 ference only to the general direction and motion of
 tbe Sun. which is probably enough for the purpose
 I had immediately in view ;  but curiosity will de-
 mand if we kn6w aught of his velocity or the na-
 ture of his course 7  Until comparatively recently
 it was considered impossible even for Astronomical
 instruments, powerful  as they were, to solve the
 great problem of the 8ideriel parallax—to measure
•quantities so small as to determine the distances of
 the Fixed Stars from us.  This, however, has been
 at last  accomplished with regard to  the star 61
 ■Cygui.  The actual distance of this star has been
 ascertained. It is 670,000 times farther removed
 from us than the  Sun,  and our distance from the
 Sun is, speaking  in round numbers, one hundred
 millions of  miles (100,000,000). This distance is so
 great that light, which  moves at the rate  of two
 hundred thousand miles (200,000) per second, would
take ten years to travel from that remote orb to the
 Earth.
   Now this star 61 Cygni has a very remarkable
 proper motion, moving through a very considerable
;«pace in the heavens every year.  Now, since we
 know the actual distance of this star from us, and
 the quantity it is  moving  through  the sky every
 year, we can convert tbat motion into  miles and
 can thus ascertain  how many miles it moves in a
 year.  Now the question is, to what is this motion
 due, to the motion of the star or the motion of the
 Sun?  Note the problem.  The star is seeming to
 move every  year through the  sky, and now what
 causes this apparent motion ?  We find the star
 is moving  exactly in the direction it would appear
 to move if  its motion were owing to the motion of
 the Sun.   We are inclined, therefore, to infer that
 the motion does not belong to the star, hut to the
 Sun, and on  this hypothesis we can compute the
 Sun's rate of motion, which is six  times  greater
 than that of the Earth in its motion round tbe Sun.
 If this, then, is at all characteristic of the amount of
 activity pervading  the whole of our Stellar Uni-
 verse, although the  skies will remain fixed so long
 as the human race will  endure, this motion will be
 sufficient, within the endless cycles of time, com-
 pletely to cRange the aspect of our heavens.  One
 can go forward, in  imagination, to the time when
 the Constellations that  now shine so brightly o'er
 us shall be rolled away to some remote confine of
 space, and their places be occupied by other suns as
 bright and beautiful as they.
  If we are going toward this star CI Cygni at the
 rate of four hundred thousand (400,000)  miles per
 hour, we will reach the extremity  of our  Stellar
 Cluster in  about two hundred millions of years!
 (200,000,000.)   These periods may seem incompre-
 hensible.  They indeed seem vast compared with
 human annals, but they are brief when laid beside
 the annals of our  Globe. If Geology is not the
 sheerest fable—if we are not to return to tbe old
 conceptions, that the rocks with their entombed
 creatures have been laid down  there purposely as
 the most mocking of enigmas—enigmas that seem
 to have meaning and yet have  none—then during
 the vastest of the periods of which we have been
 speaking, our chief existing mountains were in be-
 ing, reariDg their peaka toward different constella-
 tions and surviving in their littleness and fragility
 even these immense transitions. Extend now what
 seems true of the Sun to his other associated orbs
 and where is the repose—where the stability of our
 Heavens !  Because those very stars which shine
 on us, also shone over the Chaldeans; we spoke of
 their changeless rest, of their arrangements as being
 eternal. Alas! no, neither Space nor Time are the-
 aters of repose, and even our most stable existences
 are the seats and  subjects of activities and ever
revolving change, whose ultimate object is known
to God alone.
  It seems, then, ladies and gentlemen, as far as
 we can judge from the aspects of the bodies around
 us, that we  may consider our great cluster as being
 in ceaseless  activity ;  and that, therefore, those
other clusters whose character I intend to bring be-
fore you, are subject to something of the same des-
tiny.  If this is the case,  how little wonderful is it
 that their shapes seem  so capricious.   There is
 nothing relative to them that is entitled  to the
 name of stability, and we can view them  only as
 exhibiting to us the phases of thd successive steps
of an immense progression.  The  kind  of know-
ledge that we can alone have with respect to them,
 even should they be watched during the entire ex-
 istence of the human race, is something like what
 we would learn concerning the  terrestrial arrange-
 ment around us, if our knowledge were  gained
from a single glance of the eye, which was then shut
 again forever.  [Applause.]  No more,  probably,
 than so passing a glance  will man ever attain con-
 cerning the destiny of these nebulae.
  I shall venture no farther amid these immensi- 
Astronomy.
13
ties.  I shall not mock your  imaginations by pro-
posing to conduct them to still higher regions, away
from the  contemplation of the separate clusters up
to the Universe as in aggregate, in which each stu-
pendous  group is only an  individual.  I shall not
speak of theae aa related even like the single stars
or of the  awful motions and  careers  which must
spring out of such relationship;  but retiring at
once from grandeurs it is not yet given to the hu-
man eye to contemplate, and from bights too dizzy
for the firmeat reason, let me conclude with one re-
mark on  a queation that profoundly interests ub
all.  Looking  at theae mighty motions occupying
the infinitudes of space and apparently carrying
on the great Universe through a course of majestic
and ever varying developments, one cannot resist
the inquiry, what are the forces that shape and sus-
tain them ?  I do not mean the  mere technical deli
nition of these forces, but what is their relation to
tbe Divine Mind?  What true notion indeed have
we of force in itself?   When wespeakof thepowei
or  force  of  gravitation, for  instance, what is
it that we  really  mean?  Has the  word a dis-
tinct idea attached to  it,  or  do we  merely  de-
ceive  and  confuse  ourselves by a  phrase.—
We use the word power  to   expreas  some
thing that upholds an order, but on a close analysis
of the material Universe we do not find  aught ex-
isting there beyond simple  sequence.  Events fol-
low each  other in a regular order, and  beyond this
the Universe itself informs us of nothing.   We can-
not, however, get rid of the feeling that this order
muat be aupportcd by aomething corresponding to
an action of power or force, and the-efore we feel
impelled to inquire still more  closely, whence we
obtain our idea of power? Now it appears that
thia conception ia obtained wholly from our experi-
ence of our mental actions. It is  in fact  synony-
mous with our conception of a free spiritual act, and
therefore it seems necessary in order that the Uni-
verae be comprehensible that we  recognize Deity
not merely as the Creator but as the ever-preaent
Preaerver, Sustainer and efficient Cause of all phe-
nomena.
  Thia then, awful though it ia, is the true, ultimate,
scientific idea of the  Divine Omnipreaence.   Law
ia not even the Almighty's minister; the order of
the material  world  however close and firm is not
merely the Almighty's ordinance. The forces if
so we name them, which   expresa that  order are
not powers which he has evoked from the silences,
and to whose guardianship he has entrusted  all
things that so  he  himself might repoae.   No!
above, below and around  them is God, there his
universal  presence speaking  to  finite  creations
through finite forma a language which only tbe living
heart can understand. In the rain and sunshine,
in the soft zephyr, in the cloud, the torrent and the
thunder,  in the  bursting  blossoms and the fading
branch, in the revolving season, and tbe rolling star
there is the Infinite Eaaence and the mystic develop-
ment of his Will. [Great and continued applause] 
14
Prof. NichoVs  Lee ures.
LECTURE  III.
The Solar System___Its Plan and Mechanism___Laws governing Motion....Gravitation---Centrifugal and Centri-
   petal forces___Copernicus....Newton....Galileo___Kepler___Euler,C!niraut and D Alembert....Lea Bernouillis
   .....Macl'urin.... La (.range and Laplace___Adams and Leverrier___Discovery of  U rati us.....Its strange move-
   men's___Discovery of the Planet  .NEPTUNE — Sublime positiou of Leverrier before tbe Royal Academy of
   Paris....Concluding remarks.
  Prof. Nichol remarked, previous to commencing
his lecture, that he had, after mature consideration,
concluded that it would be advisable to divide the
lecture announced for the evening into two lectures,
as it would be impossible for him to do the subjects
which he wished to present to the audience any-
thing like justice in one lecture.  After the applause
with which this announcement was received had
subsided the eloquent Professor spoke as follows:

  Ladies and Gentlemen :  I proceed to expose,
as arising out of the mechanism of our Planetary
System, through effect of Man's profound and tri-
umphal exploration of its secrets, a discovery than
which the entire annala of Physical Science proba
bly present none  more brilliant  or  apparently
strange—to endeavor to remove the difficulties and
doubtfulness with which that remarkable achieve-
ment has seemed to some to be surrounded—and,
if I can, to clear away all obscurities connected with
its history.
  I feel persuaded that  it were needless, even at
is placed the planet Mercury; next in remoteness
we descry the brilliant Venus ; then our Earth with
its Moon ; then Mars ; then that complex group ol
small planets,  [Asteroide*,] remarkable through
their extreme diminutivenesa, and also became the
orbits in which they move so nearly approach each
other, that one mean distance might almost be tak-
en as indicating the  position of them all; behind
these lies  Jupiter,  with his satellites—the noblest
and most beautiful among the secondary constitu-
ents of our System; then Saturn, with his Moons
and remarkable Ring ; and finally,, the  planet Ura-
nus, which, until the advent of these latter revela-
tions, we deemed to be at the outer limit of Planet-
ary existence—the remotest of the regular globes
attendant  on our Sun.
the outset, to dwell with  any special attention on
the outline or general constitution of our Planetary
Scheme, for they have for  the most part passed, as
the ages have couraed along, among the details of
common knowledge; but since the entire discover-
ies, whose steps we shall  seek to follow, is but a
deduction from that constitution, I do trust I  will be
pardoned if, even here, I seek for the safte of future
distinctness to exhibit to you as succinctly as pos-
sible the most important of the elementary facts re-
lating to our System to which we shall require fre-
quently to appeal.
  1 need not more than refer to the Planetary Sys-
tem, which, as we first descry it. is alike simple and
majestic.   Resting  in one portion of Space, from
which his lustre ia diffused through the profundities
which environ him, is the Sun—our magnificent
Luminary, ranking in  glory and  corresponding  in
destiny  with the myriads of the fixed stars.—
Around  this orb, which illumines, cherishes and up-
holds  them, thoae  smaller worlds—of which our
Earth is one—roll, with admirable and unwavering
regularity, atdivers distances and in stated periods.
Nearest of all,  as shown in the diagram,
  This plan, so simple in itself, was not easily dis-
covered by mankiud, and was not arrived at till af-
ter long years  of perplexity and  toil.  The discov-
ery of it save  immortality to the name of Copek-
nious.  This diacovery. grand and sublime though
it waa. did not satisfy the ever active human mind.
The question speedily became, not merely in what
orrler are these various orbs  located, and in what
manner do they move 7—but, Can that mechanism
as a whole, be reconciled with any known mechan-
ical princi pies—are these arrangements of the Heav-
ens indicative  of the presence of Laws whose effi-
cacy we discern  among the changes more immedi-
ately around us ? It was the answer to this ques-
tion that bestowed immortality upon the great Eng-
lishman, Sir Isaac  Newton.  Prior to his  time—
 
Astronomy.
chiefly, in fact, by the sagacity of Galileo and
John Kepler—one grand principle, characteristic
of the habitudes of all bodies in motion, bad been
satisfactorily evolved  and apprehended.   It was
this: Every  body, on receiving an impulse or other
disposition to move, will move onward in a straight
line, in the direction nf the impelling force, provided
it continue undisturbed by any other force'.
  Now, on a first glance at the system  of the pla-
netary motions, it ia manifeat, that theae orbs do not
move in  atraight lines, but  in  continuous curves;
and therefore that their existing  condition cannot
be  explained, by  the mere supposition  of their
having been once set in motion  by a special im-
pulse or force: nay, it follows immediately, that,
to this primal moving power, the action of some
other disturbing force must be added, so that the
phenomena  be explained: and a little  deeper con-
sideration will show, that this second force cannot
be  one that haa merely acted at a cerain epoch
and then  ceased ;  but that,  on the contrary, its en-
ergy is unceasing or continuous.—Let us reflect for
a moment on the condition of a body moving in  a
eirele, as represented in the diagram below.
   It may easily be made plain that the body A, re-
volving  through the  circle A,  D.  E,  around C,
eannot be conceived, at any  point of its course, to
move, merely in obedience to impulses  previously
given it, and free from other restraint. When at A,
for instance—whatever theae former impulses—
its tendency, were it free, would  be to dart along
the line A B, exactly like a atone  released from a
sling; so that its natural course would be A a, in-
stead of the circular one A b,- and we cannot ima-
gine it pursuing freely the latter path, unless some
other power act on it continually—drawing it from
the right line toward which it inclinea. downward
at every moment, in tbe direction a b.  There ia
thus needed a steady and unintermitting defecting
power—capable of bending straight lines line A B,
into such curves as constitute the orbita of the Plan-
ets—to render in anywise intelligible tbe order of
our  Solar System: and «ur great countryman at
once discerned that, the inquiry into the nature of
this aedond  and necessary Force  constitutes the
fundamental problem of Astronomy.—The leading
characteristics of the second  Power did not long
escape the  persistent sagacity of Newton.  He
discerned, almost  on his earliest glance, that it
muat be  a power directed  toward tbe center of the
Sun : so that the condition of  each Planet seemed
to be this:  It is sustained in  its actual course, by
the conflict and equilibrium of two forces—one, the
result of the first impulse, or cause of its  motion.
which would induce it  to fly off into space;  and
another,  a restraining power in uninterrupted ac
tion, which of itself would cause the body to pass
toward the center of the  Sun.  Animated by this
renter-seeking tendency on the one hand, and the
centrifugal, or center-flying tendency on the other,
tbe planet Jupiter, for instance, rolls his unceasing
round in a path subject  to no accident,  and, in as
far as this goes, incapable of charjge:  and as it is
the same central  authority, merely changing in
atreugth, along with the distance of the body from
the Sun—which affects all tbe orbs of our System—
from Mercury ever hid within the solar rays, to the
remote and  inhospitable  Uranus; its  mechanism
appears aa simple as its plan—theresult of only two
of those primary ordinances, that guide  the phe-
nomena of Motion. Many profound inquiriea—deep-
er indeed than Man haa the power to reaolve—are
inevitably Buggested by the scheme  whoae sim-
plicity ha8 thna burst on ua.   What, for instance, is
thia power  which binda all these orba to  the Sun's
center?  Attraction, Gravitation—theae are
the names we  have bestowed upon it:  but what
mean they ? what the idea we  are  entitled to at-
tach to them?   Our poaitive knowledge, indeed,
goea no farther than thia—thatthe order of the plan-
etary motiona can be expreaaed  by a certain Law ;
that  the placea each orb occupiea succeaaively, in
the course of its revolution, admit of being ao joined
together; or denoted in  their totality, by the central
influence we have asaumed. Is Gravitation, then,
only a name for this succession?  Or rather, ia it
not the apparition of some primal Force or Power,
which by the order it bestows on material events—
manifests its character and influence ?   This, at
least, we know—far as  our ken at preaent extends,
whether we follow thoae singular and  majestic ac-
tivities  among the double, triple, and quadruple
atara ; or adventure still farther, even among those
awful adyta where the mightier groups of the Stel-
lar Universe take on their forms and significance—
the influence of thia august Law ever meetB our
gaze, preserving through all that exists, its match-
less  order,  and in silence  elaborating those more
perfect developments, which will occupy the Dura-
tions to come.   (Applause.)
  I mentioned in my last Lecture, that we find this
Law acting in the most remote systems exactly as
it acts in our own.  Yea ! this subtle Law diffuses
itself throughout all Space, and  curbs with its irre-
aistible might the wayward tendency of  the most
majestic and tar-off orb.  (Applause.)
  The account of the mechanism of our System,
which I have just presented, is very  far from being
the correct  or completed  one.  We  shall  find ic
neceaaary, indeed, for the sake  of distinctness, or
at leaat highly advantageous, to begin  our inveati-
gation by realizing even this imperfect view ; but
it conveys little conception of the actual structure
of a Scheme, which ia aa complex as tbat represen-
tation waa simple ; and which, bo far from present-
ing tbe orbit of any planet  as the balance of only
two tendencies, derives it from  the  equilibrium of
sympathies alike multiplied and changeable—sym-
pathies, uniting by some invisible bond  Dot  the
planets  with the Sun merely, but  every atom of
matter within our System with  every other;  and
diffusing throughout its  entire  domains  a unity so
perfect and comprehensive, that it moat  resembles
the wondrous vitality of some organized  and sensi-
tive framework. The principle of that unity is as
follows:  The  Attraction or Gravitation  which, by
drawing the planets toward the  Sun, restrains them
within a definite curvilineal orbit, ia  Dot,  as  we
have  juat supposed, confined to the Sun, or exem-
plified by bia action, alone. Speaking of it in the
usual, and,  1 believe, alao in tbe most  correct man-
ner, it is an energy or force exemplified by every
particle of matter.  So universal ia this energy, and
ao unlimited ita sphere, that even thia mote that I
bold  in my hand sends  forth an  effective notice of
its being, to tbe remotest orb among the profound
receaaea of apace; nay, alter its relative  position
by a quantity  however small, and your  act ia  felt
throughout the unfathomed Universe!  The amount 
16
Prof. Nichol's Lectures.
of inflaence it exerts,it is true, is slight, unmeasur-
able, infiuitessimal; but nevertheless an influence
it does exert on the remotest Orb that  wings its
mystic flight through Space. Before the vision of
a harmony so unbroken, of a mechanism ao vast, so
complex, and yet so perfect, the  thoughtful mind
cannot avoid being penetrated  with awe !   Ye8 !
this Fabric is indeed the offspring of Omniscience,
and under the care of a government which protects
alike the majestic and  the  feeble—within  whose
august, whose  perfect harmonies, the fragile lily
issues  from its stem, robed aa the most beauteous
queen, and the feathered aongster pours forth those
bursts of melody which are heard even amid the
solemn music of the stars.   (Great applause.)
  There are two special points in the SolarSyatem,
as we must now view it, to which I would here so-
licit particular attention.
  The  simplicity of the conditions  under  which
each planet performs its motions has now vanished
utterly awav. Not only is it attracted by the Sun;
but—since Gravitation is universal—by every other
orb having part among its arrangements, liefer once
more to the Diagram of the Planetary System, and
observe the case—say of the planet Jupiter.   That
orb indeed still obeys the influences 1 formerly ad-
verted to, viz: his own tendency to fly off into  space,
and that counteracting tendency in virtue of  which
he  would, if  unchecked, move toward the  center
of the Sun:  but beside,  he is  pulled by all the
other Planets, in most various directions ; and not
only with various, but ever-varying forces, inas-
much as each ia dragging him toward itself with an
energy dependingon ita size and distance ; and that
distance is—through those motions which are the
life of the system—always changing.  It is true in-
deed, and will be readily manifest, that of all these
powers whose office it ia to give the planet a curvi-
lineal inatead of its natural rectilineal path, the
energy of the Sun is by far  the  most important;
for, as I have aaid,  one element in the efficacy of
the power exerciaed by any body  over another, ia
the magnitude of the deflecting body : and the Sun
immenaely transcends the aggregate of all the
Planeta, which  indeed are rather his subordinate
attendants. The Sun's action, then, still determines
in the main the path of Jupiter and these other orba ;
and the action of the neighboring planets only dis-
turbs this path,  or impresses on it certain change-
able irregularities.   For instance, if tbe Sun aloDe
had acted, Jupiter would revolve around the central
luminary in a perfectly true, or accurate geometri-
cal curve, viz. the Ellipse: and that Ellipae may
still, as below, be deemed tbe normal or mean path
of that Planet—hia real one vi-
brating around it, aa in  the fan-
ciful curve in the same diagram
—a curve which is not repro-
ducedyear afteryear, but which
will pass through as  many va
riations  as  the  course  of ages
can witness, in the relative  po-
sitions of the constituents of our
multiplex scheme   To deter-
mine that normal ellipse in the
case of any Planet, might have
been no arduous task; but how different with these
deviations  from it—these ever-shifting  perturba-
tions.'  The  fidelity  with which he can trace and
estimate directions and quantities ao mutable and
evanescent, is the highest attainment of the As-
tronomer; an object indeed  most worthy of those
toils that have  occupied him since the  lifetime of
Newton.   Many  a midnight has been consumed
in the arduous pursuit: and success  in  the most
difficult portions of the enterprise, has conferred on
several names a distinction that will never  die.—
 Before me in greatest brilliance arises that illustri-
 ous triumvirate— Eulek, Clairaut, D'Alembert;
 on one side of them the great  family of the BeR-
 nouillis: on the other, our own Maclaurin ;  and
 in later timea thoae two chiefa, seated on twin sum-
 mits—Lagrange and Laplace ; from whom,  again,
 the mantle has descended and  fallen on men most
 worthy  to wear  it—a company goodly in number
 and ardent with hope ; among whom, however, the
 eye  easily discerns—as ever conspicuous—those
 illustrious  fellow-victors in  the race, Adams  and
 Leverrier. (Applause.)
  The modification of  chief moment,  however,
 which this completed idea of Gravitation impresses
 on our conception of the Solar System,  is this  ;
 No part of it can  be regarded as separate or inde-
 pendent.—each orb being united by, ties which
 cannot be severed, with  all the others, in regard of
 the chief features of its being.  So long as we re-
 gard the Sun  as the sole seat of this attractive
 energy, any Planet might be  removed  from  the
 system without other consequence than the disap-
 pearance  of a Star from our  skies:—annihilate
 Jupiter, for instance, and all others would, in that
 case, roll  onward precisely  as before, in courses
 perfectly determinate  and geometrically  regular.
 But if the merest pebble on a beach  cannot  be re-
 moved, without remote  stara discerning ita change
 of position, how entirely impossible this unobserved
 annihilation of Jupiter! > Nay, ao far from any planet
 being independent, or, aa I ahould rather say, sev-
 ered from relations with the great  Universe (for
 such, in the preaent caae, is the meaning of inde-
pendence.)—if we restrict our thoughts to its mo-
 tions or orbit, and to its absolute magnitude, tbat
 Planet may  be said to be determined by, or to be the
 result of, the concurrence of the habitudes of all the
 others.  In the caae of  Jupiter, for instance, sup-
 pose him  concealed from my sense of vision,  by
 being bereft of his power to reflect the radiance of
 the Sun;—so long, nevertheless, aa he rolls in that
 orbit, his presence must be revealed to intellectual
 vision, by his influence on the motions of the orbs
 within his reach : yea, the irregular and then unac-
 counted-for motions of Saturn, would point toward
 the reality of that Planet; and  could we aright in-
 terpret them,  they would unfold alike  the magni-
 tude of tbe force that has caused them—or, what is
 the same thing, the mass or weight of Jupiter—and
 also the variability or changeableness of that force,
 which, being interpreted, signifies the orbit and mo-
 tions of Jupiter—even as unerringly and unceasing-
 ly as the  movements of the mysterious needle  tell
 of the direction  and  intensity of  the Influence
 toward which it turns.  Let the  regular linerepre
 sented in  the  diagram below, for  instance,  be
 Saturn's orbit, in so far as that is due to the Sun,  and
 the unbroken irregular line, his real orbit.  Now, if
                  the dotted line indicates the or
                  bit that Saturn ought to assume
                  in consequence of the  action of
                   all known planets except  Ju-
                   piter; then the discrepancy be-
                   tween these laat two, viz :  the
                 /irregular unbroken  and  dotted
                   lines; would point to the  for-
                   eign influence ;  and  nothing
                   save the requisite skill could be
                   wanting  to enable us to reach,
                   through these unexplained de-
                   viations, the reality and definite
 habitudes of Jupiter.  Definite,! say, for in conse-
 quence of our thorough knowledge, not only  of  the
 reality of Gravitation, but of the precise  mode of
 its dependence on the magnitude and  distance of
 the bodies exercising  its  power—there is now no
 
Astronomy.
17
room within the range of such an inquiry, for chance,
or toleration for vagueness: to reach the fixed and
definite conclusion in regard of any point  to which
inquiry is directed, needs skill  alone—This hypo-
thesis of a successful search for  an opaque and in-
visible Jupiter, is not, however, merely  an illustra-
tive one; it is, on the contrary, the equivalent of
many inveatigations, that are far  from strange in
Aatronomy.  For instance, we  read  in worka on
that acience—often indeed to tbe marvel of those
who know not our technical proceedings—of tbe
weights of the several Planets; which are spoken
of with as  little hesitation  aa  if they had been
weighed in our terrestial  balances.  Now,  theae
are deduced in this wise : A planet being disturbed
by its neighbors, its movements are watched and
scrutinized, while  the  deflecting bodies occupy
with respect to it all variety of positions.  The ef-
fect due to each, is  thus  separated from tha total
effect; and from the amount of its influence, the
mass or weight of each planet is inferred: nay,
speaking more generally, this process of determin-
ug important physical attributes of theae orba, by
inference from their attractive influences,  has con-
stituted the principal branch of physical Aatronomy
from Newton's time until our own. Shall I dwell,
in illustration, on the lights thus obtained regarding
the shape of our own Earth?  Tbat body, like all
globes in rotation, is a  spheroid flattened at the
poles, or bulging out—as if into an attached ring—
at the equator.  The determination of tbe precise
shape of the Earth, being  of consummate conse-
quence to geographical  science, several of the
greatest of our European States  have instituted
vaat triangulations—some  of them in remote re-
 gions—that, by tbe sure methods of the Surveyor,
 this character of our globe might be defined.  lie-
suits of high accuracy have  undoubtedly  been
reached by such labors; but with all  their impor-
tance, they are not superior to  intelligence,  which
 on the same subject has reached us from the Moon.
 The motions of  tbat orb are not what they  would
 be, had the Earth been a  perfect  sphere.  Certain
 deviations are caused by the influence  of <mr equa-
 torial  protuberance: and these deviations—meas-
 ured by our modern instruments  whose precision
 approaches to the marvellous—enables us, by in-
 verse reasoning, to determine,  with undoubted ex-
 actness, how far tbe Earth deviates from a regular
 globe.  It is certainly unnecessary to  accumulate
 illustrations of a point concerning which the whole
 modern history of Aatronomy is most rich and em-
 phatic: let me conclude, therefore, with an allusion
 to that recent grand generalization of the deeply-
 lamented Bessel, which has unfolded the probabil-
 ity of opaque orba large as these spangling suns,
 revolving with a Sirius or a Procyon, around some
 common center; thua appalling oar imagination.
 already bewildered amid  the exceaa of visible
 gloriea,by the unexpected and overwhelming idea,
 that the objects which light reveala, may, atter all,
 constitute but one class, or one special though Bplen-
 did acbeme, amid thia profuaiou of created magni-
 ficence !  (Great applauae.)
   The method of this discovery of Bessf.l's—one
 of the moat remarkable of modern times—and the
 reasoning on which it repoaea, are too  remarkable
 to be permitted to eacape with a tranaient notice.
 Every star in the Heavsns, it ia known, haa an ap-
 parent proper motion ;—aometimea that motion be-
 ing altogether apparent, and in  other caaea real.
 While studying, with his usual care and sagacity,
 the changes of place exhibited through a long Be
 ries of years, by SiRius and Procyon, Besaelaaw
 that thr-y evinced a real proper motion, of  a very
 aingular description.  In both cases the Star oscil-
 lates—tbat ia, it moves  backward  and forward
like a pendulum.  Like Newton of old, Bessel
marked this as an unnatural motion—one oppoaed
to every known principle in mecbaDica.  Hia first
inference, then, waa, that the oscillating motion is,
in reality, a motion in  a circle, or other curvilinear
path, turned nearly edgeways toward us, and there-
fore taking on tbe appearance of an  oscillation.
Bnt the investigation could not atop here.  If the
path ia curvilinear,—that must be owing to a co»-
tinvous deflecting force, as" Newton held in regard
of tbe Planets:  and since no Body is visible around
which either Sirius or Procyon can be supposed to
revolve :  the conclusion is, that the Beat of thia great
attractive influence i8 opaque—concealed forever
from the  aenae of vision. The inference is so logical
that w e may not repudiate it: Surely, however, it is
moat wonderful—bringing the strange intelligence,
that thoae brilliant orbs are, after all, but one class
or species, amid tbe luxuriance of Creation!  (Ap-
plause.)
   Thua, then, Ladies  and  GentlemeD,  have I con-
cluded my exposition  of the plan, mechanism and
governing laws of our great Planetary System pre-
liminary to the unfolding of the process  by which a
mighty world was evoked from tbe boundless con-
fines of space.  It has  occupied longer than I an-
ticipated ;  but, if I have been apprehended,  what
 follows will be easily  understood.
   The researches of Physical Astronomy,  conduct-
 ed with regard to the problems I have attempted to
describe, were rapidly perfecting our knowledge of
the Planetary Syatem, wheD, in the year  1781, the
illuatrioua Herachel altered our conceptions of its
 extent, by the accidental diacovery, of tbe orb that
for aome time bore bis name, but which ia now uni-
 veraally recognized,  by the more congruous appel-
lation of Uranus. I aay accidental  for it waa by
 mere chance that Uranus waa discovered.  Herschel
 with his immense telescope had  been examining
 the Heavena for many nights, when  to  hia great
 surprise he beheld one evening an orb having a disc.
 Now our fixed Stars have no discs, that is they
 have no  surface tbat is measurable.  They  are so
| remote that when viewed through the most power-
 ful teteacopea they preaent nothing but a mere lucid
 point. So Herachel at once determined that thia orb
 could not be a fixed Star.  He noted ita place in the
 Heavena, and on the  next favorable night he ob-
 served it  again, when lo! it had moved from its
 former position. He then concluded it waa a Comet,
 and hia  first papers  in relation to it  were called
 "Papers on the discovery of a Dew Comet." But
 upon bestowing upon the  myaterioua stranger  a
 more aearching examination be soon discerned that
 it waa not a Comet,  but a Planet! farther away
 than Saturn, revolving round ourSun and  belonging
 toourSy8tem.  Now perhaps it will at once occur
 to you, why had not the exiatence of a Planet be-
 yond the orbit of Saturn been suspected before this
 accidental diacovery  of Herschel?  If all  I have
 been saying about Jupiter be  correct,  why did not
 Astronomers ascertain tbatthere were motions inSa-
 turn and Jupiter that could not be accounted for ex-
 cept by  the fact that there must have been a  Planet
 beyond 8aturn? Ifonr acquaintance with the various
 motions of Jupiter and  Saturn—the  two Planeta
 chiefly within  reach  of the influence  of Uranus__
 had been as perfect as it ianow, the  existence  of
 thia superior orb would certainly have  been sus-
 pected prior to its diacovery by ob8ervation, or had
 Uranus remained undiacoveied to this day, ita ex-
 iatence would  moat certainly be inferred from the
 motiona of the other Planeta and it would be Boon
 hunted up.  But 1781 was a long time ago  in the
 8cience of Astronomy.  Art had not then enriched
 ua with thoae splendid inatrumenta, which in mo-
 deratimes are recording quantities all butevanes- 
?l's  Lectures.
 18                              Prof.  Niche

 cent; and the discovery, therefore came to the sci-
 entific world with the freshness of a surprise.  The
 existence of those connections, however—although
 they  had escaped  our previous observation—was
 not in the least degree problematical; and accord-
 ingly the task of modifying our  previous concep-
 tions of the mechanism of the system, so that Ura-
 nus should  enter into it as an essential element—
 present, not merely in its observed place, but, by
 its influences  through  the whole  system—was
 placed before the Astronomers for solution, imme-
 diately on  the  discovery of the  exiatence of that
 orb.  Now,  this problem  evidently concerned—
 first, the queation of the  precise path of Uranus—
 the real curve it describes in its revolution around
 the Sun: and there are two very essential points
 as to this matter, requiring peculiar notice.
   The  problem itself is  this :  From a number of
■observed places of Uranus, to  determine its entire
 .path.  It is not  necessary to follow any  planet
 through  its entire course, in order that we lay down
 the path it regularly pursues.  Observation so com-
 plete, would be needful only if we had no concep-
 tion of the kind of path in which a planet muat be
 moving; but, aince we have a thorough  knowledge
 of the grand Law that regulates  the movements of
 every orb belonging to our system, a few observa-
 tions auffice, to enable us  to conclude concerning
 any orb's entire habitudes.  This ahould not appear
 strange  or  impossible.  Recollect the discovery of
 thoae remaina  of animals, by Cdvier, who upon
 finding  a few  bones imbedded  in a mound, was
 able to restore a part of the animal creation that
 had been extinct for ages.  A bone or a tooth of an
 animal  found—in your "big bone lick" is enough to
 enable the Naturalist to determine to what class of
 animalsit belonged.Justsoitis with tbe Astronomer.
   Give him a  fragment of a planet's orbit and
 from  that  fragment he will deduce the planet's
 path  around the Sun.  (Applause.)  At the  very
 outset, then, we assume as  the groundwork of our
 Theory of any Planet—and of course with  regard
 to Uranus—the  integrity of the Law of Gravitation
 in the regions  through which that planet  moves.—
 The problem, on tbe ground of that assumption, ia
 as follows: Reverting to the mode in which every
 planet must move, aa formerly represented by the
 diagram, it will be aeen that the phenomena of that
 motion are divisible into two  parta—first  the nor-
 mal Ellipse, depending on the action of the Sun;
 and,  secondly—the deviations from it, caused by
 the di8turbing action of the Planeta.   The two Bets
 of phenomena, however, although distinct,  cannot
 be determined apart from each other.-  it being
 clear that until we know something of the normal
 ellipse, we cannot compute the deviations, as these
 depend on  the distance of the Planet from all the
 other bodies  affecting it:  and again, so  long as we
 do not  know the amount of the disturbances, we
 cannot fix how much to take from or to add to, the
 observed place, in order to arrive at the normal or
 undisturbed Ellipse. The  problem is therefore by
 no means an easy one: but when our results do not
 agree with prolonged observation,  it  is  always
 open  to  U8  to  try the effect of an alteration of the
 normal  Ellipse,—an alteration,  however,  within
 limits—viz. the possibility of explaining the devia-
 tions  from the curve on which we fix, by the ac-
 tion of known  perturbing bodies. The solution, it
 will be seen, depends, in every view of it, on our
 knowledge of the mode of tlie action of these disturb-
 ing bodies.  This knowledge muat be clear and defi-
 nite ;  or  we can reach no solution at all.   If any
 unknown body, for instance, acts on  Uranus,  then
the foregoing  principles  could never  enable us,
from a few observations of its place, to  determine
its true  path:  no  more than the naturalist could
arrive at satisfactory results if he were to  attempt
to work with the tooth of one animal and the thigh
bone of another while supposing them to belong to
the same  animal.  And therefore the work of As-
tronomers must in every such  case  involve this
other suppoaition—that we  are acquainted  with all
tlie bodies that act on the Planet.  Any solution—so
far as we have yet traced ita progress—thus neces-
sarily involves three uncertainties, viz:
  (1.) The assumption of the unmodified actum of
Gravitation in regions so remote from  the  Sun as
Uranus
  (2.) The assumption that we have fixed on the
true or normal ellipse.
  (3.) The assumption that all the disturbing bodies
are known to us.
  It cannot be difficult to apprehend that, in an in-
quiry like  that  I have described,  the  facility of
reaching a conclusion, and  the certainty of reach-
ing the just one, must largely increase with the ex-
tent of ihat part of the orbit through which Uranus
had actually been traced by observation; just as in
the caae of the Naturaliat who, although be could
arrive at correct concluaions with but a tooth to aid
him, would be able to work much more speedily if
at the same time he had a thigh bone of the animal
as well.  A very few observations, if they were
accurate, and if all the disturbing influences were
known, would, in event of our possessing adequate
command over Theory,  enable us to obtain a right
knowledge of the orbit; but should any of these
conditions fail, it ia clear that the greater the num-
ber of the  planet's observed placea,  the sooner
would our defects be observed and remedied. Now,
M. Bouvard, who,  after 1820,  undertook to form
tables of Uranus, or, iu other word.*,  to deduce the
entire orbit of that Planet from observations made
during the forty years that had elapsed since its
discovery in 1781, found, on due inquiry, that it had
been seen at least fifteen times previoua to its dis-
covery by Herschel, and recorded in old catalogues
between 1690 and 1771 as a fixed star.  The record
of these positions did not, of course, detract in any
way from the merit of Herschel's discovery ; which
was, not that he saw anew star, but that the star in
queation was a Planet;  but it clearly very much
limited  the  possibilities of unrecognized  error in
any theory of the body's motions.  For instance, if
in any circle, one writes down one  set  of dots to
represent tbe places of the  planet  between  1781
and 1820, and another set to indicate those places
between 1690 and 1771, it will be readily observed
how little remains  to  be inferred, if we take  both
sets into account; compared with what would re-
main to be inferred, if only one set had been estab-
lished by observation; and it was no wonder, there-
fore, that Bouvard  welcomed the fact that the
planet had—unconsciously—been bo often seen be-
fore.  On the completion of his calculation, how-
ever, he met with a most extraordinary and puz-
zling circumstance :  The orbit he deduced was found
unsatisfactory to either set of observations.and its de-
viation from the older ones was altogether remarka-
ble ; in other words, he found that the very circum-
stance Which should have enabled him to crown his
effort with complete success, was that which, from
some unexpected cause, rendered success  impossi-
ble. So long as he took into account both sets of
observations, or, what is the same thing, so long as
he  took all available precautions to avoid  error re-
garding the habitudes of Uranus—the results of his
inquiries seemed entirely erroneous; inother words,
they gave an  orbit inconsistent with  the  facts on
which  the calculations were based.  It farther ap-
peared, that if either set of observations was as-
sumed by itself as the basis of the orbit required, a 
Astronomy.
19
result eamo out sufficiently concordant with that
set, but wholly discordant with the other set; so
that Bouvard  was obliged to conclude that these
two classes of facts were incompatible: and the
next point was, what could be the reason of that
incompatibility ?  Perhaps no conclusion was so
probable at the time as that  to which Bouvard,
amid much misgiving,  saw it expedient to come;
viz. that the old observations might have been less
accurate  than  the  modern  ones, through  the
imperfection of the  old  instruments ; and  that,
therefore,  they should  in  this  inquiry  be set
aside,  The  conclusion  was  indeed  a bold one,
I had almost said audacious: for among the ob-
servers on whose  authority  these old  places of
Uranus reposed, we find Mater and the industrioua
Flamstead, and, far above all, our incomparable
Bradley : nor waa the ingenious Frenchman blind
to the difficulties encompassing the course he  found
himself constrained to  choose.  " Such," aays he,
" is the alternative presented by the  formation of
the tables of the planet Uranus, that if the ancient
observations are compared with the modern  ones,
the first are passably represented, while the second
are not so with the precision  they  demand; and if
either set be  rejected, tables  are tbe result which
satisfy  the ones retained, but do not satisfy the
others.   It being then necessary," adds Bouvard,
"to decide between tbem, I have held by the mod-
ern observations, as being the most likely to be ac-
curate, and I leave Time to come in aid of the diffi-
culty of reconciling these  older ones, and of ex-
plaining whether it is caused by the inexactness of
these old observations, or depends on gome foreign
and yet unperceived influence to which the planet
is subjected."  And a very satisfactory light in re-
gard of the  difficulty  was  quickly  afforded by
" time."  If Bouvard  had been  right, then  the
movements of Uranus  subsequent to 1820, would
necessarily have  agreed with the orbit  deduced
from the observations between 1781 and 1820: but,
on the very contrary, the planet has since been moving
apparently withoutthe remotest regard to that orbit,
and in defiance of all known rule.  Not only, then,
waa it necesaary to reject the old obaervations in
order to sustain the authority of Bouvard's deter-
mination, but those more recent ones in regard of
whose authenticity and scrupulous correctness,not
a shadow of doubt could be  intimated, had alao to
be summarily thrown aside.  As with Kepler, in
his pursuit of the true orbit of Mars, no sooner was
the Planet, in one partof its course, brought under
control and properly enchained, than,lo! at another
part he broke from all bondage, and rushed wither
be would!  The actual state of this very puzzling
case is represented in the following diagrams:
easy rules laid down by the immortal Verulak !
Even when the temptations to go aside are slight,
men will not confine themselves to the only road
that can ever lead to a revelation of the secret pro-
ceaaes of Nature: on the occurrence of aay diffi-
culty, tbey aet a-guesaing instead ; not after that
only legitimate fashion—the way in which Geniu*
apprehends,  combines,  and follows the applicable
analogies that lie around it—but literally almost at
random, and  with no apparent aim save the desire
to avoid  confessing tbat there exists something, of
which, in the meantime, they  know neither the
method nor the cause.  It were  positively tedious,
1781

1790
1820
1S30
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IffiBSl
W If tbe line A B, in fig. 1, represent  tbe observed |
orbit of Uranus, the broken line  will exhibit the
theoretical orbit,—that  calculated from the epoch
1781  to 1840  being traced by the irregular line.
Now, the  deviation of the two lines—one-tenth of
                                           >
presents the observed orbit as determined by those
separate acts of observation between 1690 and 177L
The dotted irregular liue, on a scale only one-half of
the  previous one  (a second being represented by
half a tenth of an inch,) ii now the representation of
the theoretical orbit of Bouvard !  No marvel, in-
deed, that Uranus had come to be accounted the
puzzle of our science,—no wonder  that  so many
minds were turned to  this portion of the celestial
mechanism, in confident expectation that the anom-
alies would in time be resolved, by the occurrence
of some capital discovery.
  How difficult it is to follow, in our inquiries, the
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V If tbe line A B, in fig. 1, represent tbe observed | an inch corresponding to one second of space—is
                                             ~  tbe measure of this  discrepancy between Theory
                                                and Fact;  a discrepancy which in degree had no
                                                parallel elsewhere in Aatronomy.  Turn, however,
                                                to the diagram below, where the line A B again re-
orbit  of Uranus, the broken line  will exhibit the
theoretical  orbit,—that calculated from the epoch
1781  to 1840 being traced by  the irregular line.
Now, the deviation of the two lines—one-tenth of
                                           >
  1690, Flamstead.
  1712-15, Flamstead.
.„ 1750, Lemonnier.
£\ 1753-56, Mayer & Bradley.
  1761, Lemonnier.
  1768-69, Lemonnier. 
20
Prof. Nichol's Lectures.
 forwJn L?  ?lcmelfhe vari<5(i f^tasies brought
 Sv saSftn wuh0,lta^1°ate solemnity, as proba-
 nayncii!   *"% 'If ?ard,iDS these remarkable discre-
  '   el; °o>-shall I refer, and tbat very briefly, ex
 wePre °in™  ^?e fimPlace' the discrepancies
 fon^J?LPP "J1 tofresu,t from «c«^-not to be-
 cSes of7  ^°f onr8*stem- b°t to originate in
 custom  !ri  ^  and' acc°rdi°S to established
  ?'„'?„' a'!ke m Astro,noniy and Geology, the action
 ot  a Cornet was  invoked as  the magnus Apollo !
 One of these wandering bodies, it was said, had, in
 the course of its devious path through our system,
 come into contact with Uranus-struck  it, in fact-
 and, by introducing a new  cause  of motion, pro-
 duced the  discrepancy we  discern between the
 courae of the  planet at the  epoch of these  oldest
 observations, and its subsequent movements.  It is
 perfectly certain,  indeed, that such a disturbance
 would have produced a great deviation, or apparent
 breach of continuity. The planets path would, in
 that  case, have  consisted of  parts of two different
 orbits, joined at the point of concussion; but even
 if its course prior to and after  17H0 had been parts of
 two independent orbits, internally consistent or har-
 monious with known law—which  they are not—
 is it not clear that another comet and another shock
 were requisite after 1820, to account for the second
 breach ot continuity—that second departure of the
 planet from the course laid down by Bouvard ?  If
 one accident might, without the support of observa-
 tion of the fact, have been received as  possible, the
 occurrence of two such is opposed by all the laws of
 probability; and the hypothesis might, accordingly,
 have been rejected, even without the elaborate de-
 monstration of its  inapplicability to the details of
 either case. Nay, this  consideration goes farther,
 it forbids our referring—unless distinctly upheld by
 observation—the  anomaly to any accident what
 ever; for it is  quite  inadmissable to suppose the-
 recurrence,  in circumstances  so similar, of what in
 its very essence is  capricious—an exception, by hy-
 pothesis, to all known law or order.  We must dis-
 miss, therefore,  the  hope of receiving a solution
 from accident.—Another assumption which received
 high favor, must  also be mentioned here, as of the
 kind I term preliminary.  The calculations of Bou-
 vard, it will be noticed, rest wholly on the supposi-
 tion of the integrity of the law of Gravitation: now,
 may not these resulting inconsistencies have their
 root in the erroneousuess  of this fundamental  as-
 sumption 1   The law of Gravity extends as far aa
 Saturn : but, may it not have uudergone modifica-
 tion, in those prof'oonder remotenesses from the
 Sun, through which Uranus revolves in its  circuit?
 This  view seemed at one time a favorite with tbe
illustrious Besskl : nor has it, on the occurrence of
other difficulties, been deemed illegitimate to con-
sider it possible that Gravitation may alter.   Ia
truth, we have  no reason to suppose this  great
 Law, as now revealed, to be the ultimate  or sim-
 plest, and therefore the uuiversal and all  com pre
 hensive form, of a great Ordnance.   The  mode in
 which its intensity diminishes with  the t lenient of
 distance, has not the aspect of an ultimate Prmci
 pie;  which always   assumes the simplicity and
 self evidence of those axioms that  constitute  the
 basis of Geometry:  but there is a rule in phileso
 phy, applicable to this matter, that admits  of no
 dispute.   Allowing fully that very  few  Laws,  as
 discerned by Man, can be deemed i-aaeutially uni-
 versal—none,  it may be,  except those  first  prin
 ciples of the science of Form, by which  ao  many
of the relations of different parts of the Universe
 are determined ;—it is yet clear that we are never
 entitled to challenge the universality of Laws that
 within our experience, have nowhere tailed—until
aery other mode of overcoming the  difficulty has
  C  fT.iVail\ If -the lftW of Gravity mn«t be
  challenged, then, the  time for that is not at the
  beginning  of our consideration of this difficulty-
  j£jJt6?L  V  haVe  tri?d  every  circumatance!
  which—tbe law  remaining  entire—might affect
  the manner of  its working, and so have  demon-
  strated that what is now an apparent contradic-
  tion, may not be only one of its more recondite and
  least obvious results.—We must postpone, there-
  fore, that Inquiry, although it had the merit of re-
  ceiving the approbation of Bessel.-
   Dismissing the  idea, then, that such anomalies
  can arise from  accident, and postponing the chal-
  lenge of  the Law of Gravity until every other re-
 source  has been exhausted—we find ourselves be-
 tween  the following alternatives: Either  we are
 ignorant of all the conditions within which Uranus
 is moving,—». e. we know not the whole of the bo-
 dies  acting on that planet;  or we have not inter-
 preted  aright the  effect of known conditions.  In
 the course of a truly logical treatment cf the ques-
 tion, the  latter alternative mustlirst be examined:
 and this examination necessarily consists in a re-
 vision  of the  theory  given by Laplacjc con-
 cerning  the  action of Saturn  and Jupiter,—
 in  the  scrutiny of Bouvard's calculations,—and
 in  the  discussion  of  the  Inquiry  alluded to a
 short time  since,  viz:  whether, by  varying the
 normal  Ellipse  within  the limits which  confine
 it, and  thereby  altering the  quantities which we
 ascribe  to the deflecting influences  of those  two
 large Planets—the existing  inconsistencies may
 not be made to  disappear?  It was indeed appa-
 rently a hopeless idea, that the skill  of the author
 of the Mecan ique Celeste might here have failed,
 or the persevering sagacity of Boduvar ; but in
 presence of a difficulty so startling—of an anomaly
 bo unmanageable amid thebarmonies of our System
—no weight of authority could be allowed to forbid
our exploring every chance of error; and, accord-
ingly, one of the great men, concerning whom I am
to speak,  devoted himself at the outset to  the im-
 mense calculations necessary to construct again
from their very foundaiions,the theory and tables of
 Uranus.  In the  work of both of his predecessors,
 Leverrier  found room for modifications; and hav-
 ing effected  these, he exhausted all possibilities of
 variation in regard of thenormal ellipse. Thedifficul-
 ties were  by this investigation, to some extent, di-
 minished ; but the startling anomaly remained in
 fullest force: so that every chance of mistake being
 banished,  tbe fact stood  forth  as absolutely and un-
 questionably true—that there is a formal incompat-
 ibility between the observed motions of Uranut and
 the hypothesis that lie is acted on  only by the Sun
 and known Planets, according to the Law of Uni-
 versal Gravitation —I must here, once for all, so-
 licit the expression of your admiration in respect of
 the immensity of the sheerest and moat unmitigat-
 ed toil, undergone in this great research.  Tbefinal
 results  of Astronomy are usually so  dazzling that
 tbe mind of tbe rapt student easily goes  in with
 the idea that the  road leading to them is  equally
 pleasant; a road through gardens—among flowers
 —and by  running brooks!   Alas! alas! it is a bard
 and moat weary  path—across a moor without a
 blossom!  No Siberian  steppe can  be more  arid
 than the sphere of theae labors of Leverrier ; nay,
 in  every  portion of Astronomy  the  labor of  dry
 calculation has  become so overpowering  tbat the
 resources of Analysis have of late been peraever-
 iugly bestowed, on the discovery of modes of short-
 ening and checking these processes,—as one of the
 most effective means of increasing our power.  Ll-
 vkrrier  was detained amid such calculations  dar-
 ing the season of the year in which, as a  first ap-
 proximation had informed him. his Planet waa  pis- 
Astronomy.
21
ing rapidly from that position In  the slues which
alone, for a whole year would permit of its being
seen.  But he hurried nothing—shrank from noth-
ing ; he bore himself aa  the high philoaopher, to
whom guesses are nothing, unleas verified ;  and he
knew that in questions like these, it was only the
compatibility of accurate results that could lead to
Truth.
  Aswe advance, we get rid of uncertainties. The
problem is now reduced to a  simple  form; viz:
Can the anomaly beexplained by the supposed action
of a foreign and hitherto unknown body on Uranus ?
Here, too, however,  is  choice of hy potheses. Ia
that foreign body a new planet, or is ic a body con-
nected with Uranus—a satellite? The I atter id ea waa
favored by  aome Astronomera ; but on grounds
worthy of no more attention than previoua conjec-
tures respecting the Comet.  If Uranus waa so
disturbed by a satellite, that satellite muat have
been large, and therefore we ought to have  seen it
even at that remotenea8 ; but what is of conclusive
importance, the description of perturbations which
alone could have been produced by a eatellite, ia
not the one with which we are at  preaent concern-
ed.  Thoae would be  essentially oscillatory,—the
satellite being now on one aide of  Uranua, and now
on  the other; and perturbationa  of that kind are
not sufficient for the phenomenon  befere us.  In ao
far as analogy goes, then, we are forced on the con-
ception that the diaturbing cause may be a Planet
—yet unseen by tbe Telescope.  Thia  idea, lam
perfectly  aware, waa not a novel one.  In  a world
so buay aa oura, and where knowledge, poaitive and
fanciful, belief and  idle  conjecture, are mixed up
and whirled together amid our common apeech, in
grotesque but inaeparable union ; it would indeed
have been wonderful if thia  most natural assump-
tion had  been overlooked: but rather than seek
amid so strange a chaos for the origin and indica-
tion of a grand verity, let us give the credit to the
true workmen, to whoae minda the conception was
doubtless first recommended by its general verisimil-
itude, but who were moved thereby, only to work
the thought through all its relations, to inquire—in
due lealty to Nature—whether this conception waa
really conaiatent with her arrangements, and could,
when fully carried out, explain the difficulty in its
details  ?   " That  man  alone discovers  who
proves."  It is time the truth  were apprehended,
that there is no royal or easy road to Philosophy.
  The Inquiry,  then,  points  to  a New Planet.
That word, often carelessly pronounced, became, in
the hands of Adams and  Leverrier alone—a defi-
nite and practical tbongbt.
  If a New Planet—Where? By tbe general order
of our Syatem, certain  a priori grounda of approxi-
mation  were afforded, which could hardly be much
in error;—at all eventa. they greatly aimplified the
earlieat calculations.  First, it ia  a law among the
known planeta, that they lie nearly on the plane of
tbe 8un'a equator. Suppose, for illustration, the Sun
represented by a ball laid on the middle of  a table,
then all the Planets would require, if  represented,
to be laid nearly on tbat  table;—no one would be
found far above or below it.   The new Planet pro-
bably following that law. we Bhould look for it in
the Heavena only through that zone, whoae center
is the Ecliptic, or the annual apparent  path of the
Sun; nay, for conformity's sake, we may suppose
that the planet is in the Ecliptic ; for ita utrooat pro-
bable deviation from that line would  produce no
sensible error.  Secondly, there is  another remarka-
ble law, whoae origin ia quite unknown, but whoae
authority, as far aa the limits of the orbit of Uranus,
waa undoubted. It ia this—Any planet—speaking
in general terms—is half aa far away from the Sun
as the one next in order in ascending, and twice aa
remote as tbe one next in order in descending.  If
the distance of the Earth, for instance, be repre-
sented by 1, the distance of  Mars is 2, and that of
Venus|; and so through all the  known aystem.
Tbis law ia aufficientiy general to have been the
cause of tbe discovery of that aingular group ofin-
finiteaaimal bodies between  Mars and Jupiter—the
progression having there indicated a hiatus, to be
filled up by a new  body; and that group—resem-
bling the elements orfragmentaof aaingle planet—
occupiea almost the requisite orbit.  It waa no un-
justifiable hypotheaia, therefore, to extend thia law
to the planet now aought—eapeeially as other al-
though minor considerations sustained the  conclu-
sion  regarding the body'a probable distance.  The
question thua became aa follows :
  "Is it possible that the inequalities of TJranus are due
to the action of a planet situated in tbe ecliptic, at a mean
distance double that of Uranus ? And if ao, what la the
place of the  planet, what Ita mass, what th« elements of
the orbit through which it moves ?"
   It appears simple  now :  but assuredly this was
the most daring effort  ever undertaken by Man.
The Earth is distant from  the Sun  almost by the
enormous space of one hundred millions of miles.
Uranus is nineteen times farther off, and this sup-
posed planet must, by hypotheaia, be yet twice as
far 1  Can  it be, then, that  the thought of Man, as
the faithful interpreter of Nature'a Lawa—sympa-
thizing, as it were, with her uuiveraal  designs—
can  walk  safely amid  profundites so dread, and
evolve the necesaary complements to our planetary
Scheme ?  Are we bound so closely with tbe sys-
tem to which we belong, tbat not a vibration can
escape ua?  Ia the human Mind  indeed so inde-
feasibly coordinated, even with the grandest laws
of this Univerae ?
   I  wish 1 could follow—with the hope of being ac-
companied by my hearers—the march of LeVer-
 rier and Adams,in the unwinding of this memora-
 ble problem: but their sagacity having for its es-
sential or only possible garb, the symbol's and pro-
ceaaeaofour most recondite Analysis, it i8 merely a
few vague conceptiona that 1 can expect to give  of
 ita character and elevation.  In what I do Bay, I
ahall abide by the processes of  Leverrier, partly
because they  are more  susceptible of representa-
 tion than the more  general developraent8 of Mr.
 Adams, and alao because, as a matter of fact, they
 led to the first diacovery of the actual existence of
 the  body aought for, and therefore first proclaimed
 to the world thia new triumph of Science.—There
 are  a few, although only  a few,  distinct points,
 which may be generally apprehended.
   It cannot require acquaintance with technical
 analysis to enable one to apprehend  the nature of
one means toward  the solution of this problem,
 viz: the method adopted by  Leverrier,—of ap-
proximation.   A view of the conditions that must
determine a final result of only a rough description,
 would  evidently conduct  to limits  within which
both the place and the masa of the planet muat lie.
 After the different quantities involved are assorted
 according to their  relations, it is not  difficult  to
conceive how a view of  their mode  of  arrange-
ment would lead to  the  conclusion that—without
 attempting minuter appreciation—the'attributes of
this body must be confined  within certain distinct
numerical expresaiona; and tbat—as the two most
important  attributes—the  place of the orb  at  a
certain epoch,  and its mass—might be roughly
separated, the one  having  to do chiefly with the
direction of the disturbing force, and the other
solely with ita magnitude,—it wa8 no unlikely thing
that a preliminary statement with regard to both
could  be made:  which—being accepted—would 
22
Prof. Niclwl's  Lectures.
  greatly facilitate farther inquiry. Lbverrier's first
  conclusion was as follows:
   '' There la in the whole Ecliptic only one region In which
  the perturbing planet can be supposed to be placed, ao that
  It account for the irregular movements of Uranus.  On the
  first of January, 1800, ita mean longitude must have been
  between 243» and 252°."
   My hearers will readily appreciate the extent of
  new knowledge acquired by this step.  By our first
  and fundamental assumption, the  new planet had
  to be sought only in the Ecliptic—in that one great
  circle around the Heavens, and not indifferently, in
  any place of the dazzling vault.  The meaning of
  the foregoing numbers is as follows : To fix or refer
  easily to the place of  a star in the ecliptic, we sup-
 pose that whole circle divided  into three  hundred
 and sixty equal parts, named degrees; and we be-
 gin to reckon these from a determined point, viz. the
 first point of Aries—passing all round that great
 circle.  Observe now  the limitation previously
 made; the place of the unknown planet  was con-
 fined by it within the  brief space of nine degrees,
 in a circle consisting of 360°.
   This important limitation conducted immediately
 to a much more distant enunciation of the planet's
 place. Leverrier soon discerned that the necessity
 of satisfying all the relations of the unknown quan-
 tities  would not permit an uncertainty  as to the
 planet's place of even theae nine degrees, and hav-
 ing  determined the limits of its mass, he reached
 the following proposition:
   '■ That all the observed motions of Uranus could be ac-
 counted for by the perturbing action of a planet, the ele-
 ments of whose orbit were primarily assumed, whose lon-
 gitude on 1st January, 1800,is252", and whose eccentricity
 and the loDgltude of ita  perihelion were determined by
 processes he had just explained."
   The mass of the planet he had between the mass
 of Uranus, and one three and a half times as large.
   From the previous theorem it followed that on
 the 1st of  January, 1847, the heliocentric longitude
 of the required orb must be 325° ;—an  astonishing
 approximation,  with which most men would have
 been satisfied; but it only informed  Leverrier
 that a farther accuracy might yet be obtained!
   On the 31st of August, 1846, LEVERRiERproduced
 his last great paper to the Institute.   During his
 former  researches,  or previous to his having se-
 lected any part of the ecliptic  as more likely than
 tbe others to contain the new Planet,  he had con-
 fined himself to consideration of a certain number
 of the facts ascertained in regard of Uranus—se-
 lected because of their fitness  to yield a first  ap-
 proximation ;  but to give his  work the utmost pre-
 cision of which  it was susceptible, he now em-
 ployed the whole of the nineteen old observations
 made between 1690 and 1771, and a very large num-
 ber of the  two hundred and sixty-two places found
 in the records  of the observations of  Greenwich
 and Paris  between 1781 and 1845 :—each of these
 separate facts giving a distinct equation of condi-
 tion, as it is termed, or a numerical value of certain
 combinations of the unknown quantities,  viz , the
correction of the elements of the orbit of Uranus;
 and the mass, and the elements of the orbit, of the
Planet sought for.  No fewer than  nine unknown
 quantities were involved in this work; and he re-
 duced  his  equations  ultimately to the number of
 thirty-three. The treatment of these, again  in-
volved immense toil;  and it was while undergoing
this last labor that Leverrier had the mortification
to observe  that before his calculations could possi-
bly close, the planet, in its apparent course through
the sky, would  have  passed for the  year from a
position the most favorable for its being seen.  His
labors  at  length were terminated; and he  an-
 nounced finally to the French Academy the follow-
 ing elements:
   Radius of the orbit.  3B'l 54 times that Of the Earth.
   Period of revolution, 217 387 years.
   Mean longitude,   7 31847
    January 1, 1847,3 __1__
 •Mass.............   9300
 From which,  an easy  computation showed,  that
 the true heliocentric longitude on 1st January, 1847,
 must be
                   326° 32
           instead of 325°
 as roughly given by his first approximation.  How
 singular that scene in  the Academy I  A young
 man, not yet at life's prime, speaking unfalteringly
 of the necessities of the most august  Forms of
 Creation—passing onwards where eye never was,
 and placing his finger on that precise pointof Space
 in which a grand Orb lay concealed ; having been
 led to its lurking-place by his appreciation of those
 vast harmonies, which stamp the Universe with a
 consummate perfection !  Never was there accom-
 plished a nobler work, and never work more nobly
 done!  It  is the eminent characteristic of these
 labors of Leverrier, that at no moment did his
 faith  ever waver :  the majesty of the enterprise
 was equalled by the resolution  and  confidence of
 the Man.  He trod those dark spaces as Columbus
 bore himself amid the waste Ocean;  even when
 there was no speck or shadow of aught substantial
 around  the wide horizon—holding by his convic-
 tion in those grand verities, which are not the less
 real because above  sense, and pushing onward
 toward his New World!  (Great applause.)
  We touch on the close of this long and noble  en-
 deavor, viz : the actual discovery of the Planet.—
 There are several pohsts connected with this act,
 which it is of extreme importance that my readers
 rightly understand.  Tbe discovery of a planet by
 the telescope can be made only in one of two ways
 —by the observation of one of those two features
 which alone distinguish  such a body from a fixed
 star, viz: its possession of a palpable disc, or its hav-
 ing planetary motion:
  If the  orb is of sufficient magnitude to exhibit a
 measurable disc to the telescope employed in  the
 research, its discovery is comparatively easy; for
 the feature in question wholly separates it from the
class  of the Fixed Stars.  These mighty orbs,  al-
 though of the magnitude of Suns, are seated so pro-
foundly  in space, that to the largest  instrument
 with which we have yet examined them, they ap-
pear with a brilliance augmented indeed in propor-
tion to the size of the telescope, but still only  as
points, severed essentially from those small orbs
 whose dimensions we can descry and compare, and
which are oar companions and neighbors.  It was
this attribute which revealed Uranus to Herschel ;
 and Leverrier threw out the idea that the actual
 mass of Neptune, and the augmented power of the
 Instruments that can now be pressed into service
of such a research, favored the expectation that, by
its posBeasion of a visible disc, and therefore with-
out any overpowering labor, this new Planet would
 be found.  In several parts of this remarkable work,
 Discovery seems  to have been attended by a pro-
 pitious chance;  and  although, as we  shall after-
ward see, the grounds of Leverrier's expectations
were  here fallacious,  his prediction  of the ac-
tual apparent size of Neptune approached surpris-
ingly  to the truth.  This disc, however, although
definite and measurable, is so small as to be almost
illusory; and it was not by it that the  Planet was
discerned.
  Unaided by any visible disc,  the Explorer has
only one other resource: among the multitude of
small stars in the quarter of the Heavens where 
Astronomy.
23
the unknown orb is conceived to lie, he requires to
ascertain whether any one has a planetary motion.
But this cannot be discerned by a  single inspec-
tion.  The motion at remotenesses like those with
which we  are now being conversant,  must be so
slow, that, for the brief time of  one night,  or even
of several nights, it may be  virtually equivalent to
stillness ; so that it cannot be detected save in one
way, viz : the careful comparison of the state of the
Heavens on one night, with their state on some
other night, separated from the first by a consider-
able interval.  Now, this comparison is not easily
accomplished—nay,  it involves great labor; it re-
quires that an accurate mapbn made of all the small
stars in  the region of the  sky under scrutiny, at
these two several times ; and to do this—to map the
small stars in any region of the sky even once, in-
volves a labor ao great—taking the necessary ex-
actitude into account—that Leverrier  gladly ex-
pected  the deaired  reault  from the  viaibility of
a disc, and Fortune waa again favorable!
  For many years a great  enterprise has been in
the act of being performed by the Academy of Ber-
lin—chiefly through the instigation  of the illustri-
ous Bessel.  Convinced of the great importance of
the work, especially with regard to such discoveries
as this—the Academy undertood the mapping—
with  all the precision which our modern Inatru-
mets render possible—of the small stars along the
entire Zodiac, or along that belt of the sky, where
—from the analogy of the other parts of our system
—new planets might be expected to be seen.  The
labor required to achieve this was enormous ; and it
was divided among a great number of persons, hav-
ing requisite instruments.   Now, it bo  happened
that the map of  that  precise region where the new
planet was expected, had been completed by Dr.
Bremiker; and it was printing, or just printed, at
Berlin :—I believe that the Observatory of Berlin
had obtained the proof-sheet. The Astronomers of
this Institution were thus in a position of power re-
garding such inquiries, enjoyed  by no other Obser-
vatory  in  exiatence: they had simply to notice
Bremiker's Map  and then the Sky—observing if
there was a discrepancy between the two pictures,
that could be   accounted  for  by the  planetary
motion of some  one star: so that—with their re-
nowned sagacity, and the excellence of their instru-
ments— an inspection of tbe Heavens  on one clear
night might accomplish the resolution of thia great
problem.  And thus  it even was ; the Planet was
discovered  actually by M. Galle, on the very eve-
ning of the day on which he received the letter of
Leverrier indicating its place.  (Applause.)
  As ascertained by M. Galle, the heliocentric lon-
gitude of the body for the  epoch  of 1st January,
1847, would be
                            327° 24
        The predicted longitude  326  32
as before  stated.  The  difference  was, therefore,
less than one degree or only fifty-two minutes! _
  I am, indeed, aware that few grand discoveries
have ever been achieved without some degree of
previous disappointment on the  part of the discov-
erer.  More or less enveloped in shadow they loom
for years before his anxious eye, but the entire  an-
nals of Observation probably do not elsewhere'ex-
hibit so extraordinary a verification of any theoreti-
cal conjecture adventured on by the human spirit!
M. Leverrier received the cheering  intelligence
after  he had concluded his last paper to the Insti-
tute on the subject; and his bearing was too strik-
ing and characteristic to allow me to omit reference
to it.  "This success,"  says he,  "permits us to
hope that after thirty or  forty years of observation
on the new Planet, we may employ it, in its turn,
for the discovery of  the one following it in its order
of  distances from the Sun.  Thus, at least, we
should unhappily soon fall  among bodies invisible
by reason of their immense distance, but whose or-
bits might yet be traced in a succession of ages,
with the greatest exactness, by the theory of Secu-
lar Inequalities."  Verily, what  a man is this !  On
hearing that he had  done a deed  unparalleled in
scientific  history—that to his thought of unexam-
pled daring, even God's  Starry Universe had  re-
sponded, and in its own splendid and imperishable
language  pronounced its verification—not one re-
flex glance on himself, not a complacent smile on
the isolated ME, which amid these infinitudes had
been privileged to do a work, and therefore claimed
and panted for its special  homage, but  a firm—a
rejoicing and withal  a  reverential hope aa to the
progress of that Humanity,  from participation with
which his  own strength will come—for the progress
of that  Human Spirit whose earthly deatiny will
not cease until, after the  evolution of agea, that
grand material imagery lies in all its mysterious
gorgeousness prostrate as spoils at its feet. (Great
applause.)
  [Dr. Nichol here closed  his lecture, although he had to
leave untouched  several of the most  interesting points
relating to  the discovery of the planet Neptune ] 
21
Prof. Nicltol's  Lee urcs.
LECTURE  IV.
Continuation of the history of the Discovery of the Planet Neptune___The Diacovery of the  Planet not the reault
   of Chance.
   Ladies  and  Gentmemen :  I proceed with the
-great subject which occupied us the last  evening.
 I confess, however, that some of the questions that
- are to engage us have to me less than their natural
 attraction, because I can hardly do what alone I
 wish, viz.: declare my  opinions and  knowledge
 concerning them, without undergoing the hazard of
 being considered aa if hrcontroversy with men on
 this aide of the  Atlantic, who do not think as I do,
 and whose learned and professional inquiries may
 have led them to conclusions not in harmony with
■thoae toward which we  are inclined in Europe.—
 Let me, then,  at the outaet, with all possible dis-
 ■tinctneaa, utterly diaavow the attitude of controver-
 sy, as unsuitable, ungraceful on thia platform.  So
 soon aa the important inquiries of which we are
 speaking have reached their close, and the Planet
 .Neptune is received aa a thoroughly understood el-
 ement of our Planetary System, with relations all
 liied and definite, then whatever of speciality or
 incompleteness  may have been in the views of any
 oae during that  period of imperfect knowledge or
 of twilight, will doubtless be explained, reconciled
 and  amplified by its authors:  at least, it is far
 from necessary tbat I, whose business it now is sim-
 ply to unfold in language fitting our opportunity, the
 aaanner in which my own reflections have, in the
 meantime, presented to me a difficult and remarka-
 ble subject, should place myself in conflict with
 others, especially when the occasion is wholly un-
 favorable to a critical analysia of the grand causes
 of our difference.
    With theae preliminary and protective explana-
 4ioas,then, let us now pasa freely and unembarrassed
 along our course.  In my last Lecture I endeavored
 to bring my audience down to that point in the his-
 tory at which the Telescope at Berlin  verified the
 remarkable prediction of Leverrier—the point at
'Which it was revealed that tbe simple  power of
> thought—by carrying hia fixed conviction in the
 perfectneas of the  harmonies of the Universe to Its
 legitimate concluaion, he had laid hia finger on the
 spot occupied by the orb he sought for, with an error
 equivalent only to about one  and two-thirds the
 'apparent diameter of the Sun.
    L«verrier's prediction was that at  a certain
 time the planet would occupy a space indicated by
 She numbers 326° 31', and the  position it actually
 occupied when  discovered  was aa follows: 327°
--24/, constituting an error of less than one degree of
 apace.  [Applause.]  Now,  to  give you an idea of
 4he  proximity  with which the prediction corres-
 ponded with the fact, 1 will state that this space ia
 "net  about one  and two-thirds the apparent diame-
 ter of the Sun.  This space, howpver, although
 *m&U in appearance, is yet undoubtedly very large
 in quantity.  It will be found, when reduced to
 aniles, to be about  40 000,000.  A very small space
 'indeed, when seen from this enormous distance,
 the remoteness  being so vast.
    I need not inform you that since the  discovery of
 TNeptune it has been watched with every sedulous-
 zl&m, ia order that by an accuracy of measurement
which Art now enables us  to transport into these
far spaces, its  entire dimensions aDd the nature of
its orbit might be  known. I mentioned the last
evening that from a small portion of any observed.
orbit the application of the law of Gravity enabled
Astronomers  to deduce the entire  of it; and for-
tunately a happy  discovery—made first, I believe,
by an American Astronomer, Mr. Leart C. Walker,
and about the same  time, or very soon  after, also,
by an observer of Germany—greatly accelerated
the period when, on the ground of fact, the leading
features of Neptune's orbit could be correctly de-'
duced.
  My hearers will remember that when exhibiting
the extraordinary  eccentricities of Herschel's orbit
at the last Lecture,  1 mentioned that the orb had
been  seen  before  it  was discovered  to be  a
planet,  and  tbat  these old observations  were  of
great assistance in  determining its perturbations.
Now a happy accident of this kind occurred with
regard to the planet  Neptune.   The planet, it was
found, had been seen twice by a Frenchman named
Lalande, in  May,  1795;  and this Astronomer so
narrowly missed  the honor of adding a fresh con-
stituent to our system, that he rejected his ob-
servation of May  8, because it did not agree with
that of May 10—thus losing the momentous truth
he would immediately have reached, through inad-
equate faith in  his  observations   If, instead of
doubting his observations, he had watched the orb,
he would have discovered  the  planet; but instead
of doing so,  just in one of those moments of care-
lessness that will occasionally come upon the most
accurate and careful persons, he aaid, " One of my
observations muat be wrong, and I will blot it out,"
and bo he did, and with it he blotted his own name
from the scroll of immortality.
  Although this observation was not, under the cir-
cumstances,  extremely creditable to Lalande, it
has been, as I have said, of the very highest con-
sequence to us, for by extending the observed por-
tion of the orbit over a very considerable space, it
has enabled us even so early  to reach with much
certainty the leading facts connected with the mo-
tions of Neptune—having revealed at once the
true distance of the Planet, and its period of revo-
lution.  And here it is that  the strange intelligence
came to us which seemed to impair the beauties of
those labors of Adams and Leverrier, which, ac-
cording to an impression  that in this country has
become moat prevalent—not only withdrawing
from them  all pretension  to perfection, but  even
disentitling them to their assuredly just claim of
having beenthn certain, the unerring means of dis-
covering this New  World, and indicating its place
 amid those remote  infinitudes.   The  intelligence
 indeed was of a nature that could scarcely seem
 otherwise than startling, for it showed that in that
 part of their inquiries which attained the distance of
 Nkptune, according to Bode's  law, both of theae
 great Astronomers were in error, and not by a trifle
 —a number small in relation to tbe kind of numbers
 we use in pursuance of such inquiries,  but even by 
                                         Astro

 a sixth part of the Planet's entire distance from the
 Sun—by the enormous space of six or seven hun-
 dred millions of miles ! I
  I think the audience mustremember that I said tbat
 when these two Astronomers  began their investi-
 gations, they assumed two things : First, that the
 new orb would lie in the same plane with the other
 Planets ;  and secondly, that according to Bode'b
 law, it would be lying about twice as far away from
 the Sun as Urauus, which would make it thirty-eight
 times farther away from the Sun than  the Earth is.
 Now it has been found to be only about thirty times
 as  far from the Sun as the Earth.  Thia ahowa ua
 that throughout the whole of their calculations, thia
 enormous error of distance extended.  It is a very
 remarkable fact, certainly, that a law which pre-
 vails in bo many instances should be found to fail in
 this  particular  instance.   But it often happena
 when laws whose principle we do not understand
 are extended over a considerable apace tbat they
 fail.  Now the origin of Bode's law is entirely un-
 known: it is what is called  an  empirical law, be-
 cause we donot understand the principle upon which
 it acts. The failure of Bode's law, however, was
 not the remarkable circumstance; the remarkable,
 the extroardinary circumstance was that, with thia
 great  error in  their calculations,  these Astrono-
 mers ahould have come to a true conclusion!  The
 audience will observe tbat this error in tbe distance
 of the planet involved alao an error  in ita revolu-
 tion, for the revolution of an orb  depends  upon its
 distance from the Sun.  While  Leverrier  and
 Adams auppoaed Neptune revolved round the Sun
 in 217 yeara it  actually goes round in about  166
 years—making a difference of 51 years !!
  I cannot marvel that the announcement  of this
 extraordinary and certainly unlooked-for discrep-
 ancy threw over  the whole inquiry an exceeding
 doubtfulneaa ; and thia not merely in the current of
 popular opinion; for  the more thorough our know-
 ledge of the perfection of the Celeatial mechanism,
 the  more perfectly we see that  in  the  mighty
 sphere around  ua, where every atom is fixed and
 adjusted by eternal  laws, and cannot in any way
 be  altered  in  position without a corresponding
 change of its relations  with whatever else exists,
 even the  less  likely did  it appear that  the sup-
 posed relations of  a false  planet with  Uranus
 should have sufficed to conduct us so unerringly to
 the discovery of the actual orb.

  [The Lecturer here drew several diagrams upon
 the  blackboard for the purpose  of illustrating  the
 impossibilities of mere chance having aught to doiu
 the discovery of Neptune.  The succeeding pas-
 sage of the lecture contains a full statement of all
 the ideas illustrated upon the blackboard.]

  Tbe case  is,  no doubt,  a strange  one; but  as
 nothing can happen within this scheme  of ours with-
 out full and adequate cause, we proceed without
 desponding to endeavor to  unravel the mystery.—
 And at the outset 1 would  reiterate it as a truth
 beyond the reach of question—one which we must
 hold constantly in our  thought,  that  two  planeta
 cannot possibly  explain the same thing.  The per
 turbations of Uranus which conducted  to thia great
 diacovery. flow from one orb alone—the trub Nep-
 tune, and notthe false one; and the latter cannot
 peraonate the former in regard of its actions  with-
 in our System.  The laws  of the Universe are too
 fixed and definite to permit these personations and
 exchanges.  Each atom in this immense fabric has
 its  unchangeable and  incommunicable place and
 functions;  nor can any individual put off or  ex-
change his duties for the responsibilities ol another.
wmy.                                      25"

   [The speaker here drew another diagram  oa t&e
 blackboard, for the purpose of enforcing  still more?
 strongly the ideas contained in the  above section.
 of his discourse, after which he continued:]
   lam now done with  preliminaries.  Yon -will
 perhaps excuse their tediousness, for I think yon
 will see tbat we are dealing with what  lies much
 out of the direction of ordinary thought, and wbiekt
 therefore it is not easy to clothe with a customary-
 garb.  My sole object is to accomplish  this, and
 therefore I have hazarded apparent repetition, and*
 have not regarded scientific forms of exposition and
 speech. (Applause.)
   Let me now remind my audience of the essential
 aim alike  of Adams and Leverrier.   It was, te
 lead to the discovery of the disturbing planet—to lead,
 1 say to its discovery, to point to that part of the-
 Heavens where the telescope ought to find it—an
 aim grand and adventurous indeed—but which waa
 essentially  limited—(a  fact,  by-the-by,  to which)
 sufficient attention has not  been drawn)—for they
 did not undertake wholly to produce Neptbnh—to-
 unfold through calculation, what afterward woulA
 be deduced from facts; they sought  for nothing est*
 cept to indicate that part of the sky where  tb*-
 planet was now lurking, and where the telescope
 might detect it.
   In beginning the solution  ofthis remarkable prob-
 lem, they assumed Neptune's distance, reposing
 with confidence on Bode's law.  Now it appeared
 to many Astronomer's, English as well as foreign—
 looking at the question in an a priori manner—that
 this law might be  inaccurate,  and therefore that
 the  solution had little chance of being a true one ~
 and doubtless this very fear  must  have occurredi
 alike to Adams and Leverrier ; but ere they had
 proceeded far with tbeir work the most  imports:^
 truth came out tbat, at an epoch the most momen-
 tous of all,  the two planets, Neptune and tJramasv
 held tbat precise relative position in regard of tbe
 Sun which rendered error in distance of no moment-
 in respect of the new planet's place—the position.
 where it affected their estimate of the planets m&aa
 only.
   The following illustration will perhaps enable yose
 more readily to grasp this idea.  Suppose the Sso,
 Uranue and Neptune to be situated with  respect to-
 each other  as represented below,


          ©      *      i   i
         Sun.   Uranus.   n«
                          Neptune.

 which were their relative positions in 1820.  It wil$
 be apparent, at once, tbat it matters not what the
 distance of Neptune may be, whether it is situated
 at 1 or 2 ; the kind of influence it will exert ove?
 Uranus will be the same whateverits diatance.  To»
 exercise a  given degree of influence, however,  tbe-
 mass of the planet must increase as its distance in-
 creases, and viceversa.  But further, in a few years*
 these orbs, 1 and 2, owing to the difference in their
 velocities,  would be scattered—would occupy di£-
 ferent  positions in  respect to Uranus;  when, of
 course, their influenceupon that planet would cease
 to be similar in kind, that is, they  would not be
 pulling Uranus  iu the same direction.
  Thia fact, however, (the conjunction of the two
 planets in  1820) although perfectly adequate to
 explain the conformity of the two orbs, within the
 period bordering either aide of  1820 will not, it is>
 evident, extend much beyond that neighborhood—
 the different velocities of bodies at  so very differ-
 ent distances would cause them soon  to diverge—so
 that in 1846, when the discovery  was actually 
26                              Prof.  NichoVs  Lectures.
of
it
in respect of Uranus do not esrregiously  differ:
throughout the course, the kind of the perturbation
must  be the  same in either case, except in the
brief part of the  orbit,  a b, fig.  1, marked by a
thicker line, during Uranus' motion, in which  the
bearing of the inequality would in the two cases
be  opposite.  This would certainly be the case  if
the  orbit  of the planet were circular, as I have
represented; but it may be  easily supposed, that
by the adoption of an elliptical or oval, instead of a
circular orbit, this cause  of discrepancy might be
made to disappear, simply by effecting the transfer
of the point of conjunction in the case of fig. 1, to
a point corresponding with the true epoch, as rep-
resented in fig. 2.
  [The lecturer here had recourse again to the black-
board, on which he exhibited and illustrated in va-
rious ways the conjunctions, accelerations, and re-
tardations  of Uranus  occasioned by the true and
false planets—the orbit of the true planet being
represented in fig. 2,  while that of the  false
planet is represented in fig. 1; he also represented
the  difference between two classes of perturba-
tions,  the first class called Periodic inequalities,
which refer exclusively to direction,—the second
class called Secular inequalities, which relate  ex-
clusively to distance.  All these things he made to
appear very simple by means of his diagram, but
we cannot present them to our readers  inasmuch
as we were unable to report the Professor's black-
board.  In conclusion he said :]
  It seemed to me to  require this additional ex-
planation  to give to the view of the  subject  I de-
sired to address to you its due completeness, and
to entitle me to assert that in all respects the la-
bors of the illustrious men whose footsteps we have
been tracing,  come forth  rounded amd*  beautiful,
characterized by the loftiest powers, for which are
yet in store even nobler triumphs.   Neither, per-
haps, was it wholly unneedful in vindication  of
Man's  existing knowledge of our System's Me-
chanism.  Facts—the facts requisite  to enable us
to apply theories, cannot of course  be hastened on
—we must wait and watch  as the ages  unroll
themselves; but in respect of our ability to under-
stand them when attained—I cannot now discern
a term. It is not poaaible that in  this place I can
demonatrate or confirm it, but yet in confidence I
allege that a time is not far distant when  we shall
be able to extend, ns it were, a great chart through
our System, on which every orb belonging to it
will leave  an impress of its relations as clear  to
the skilled eye, as the fine mechanism of a leaf to
the microscope of the Botanist; ay, building on
these proud labors  of ours—it may  be,  as time
shall  pass, that  with hand as firm  among those
grand Stellar Systems, having unrolled their order,
we shall stretch there too even such a  plan and
chart—to  which  the  throbbings of these  entire
Starry Universes  shall  report  themselves, and
where they will impress their harmonies for the in-
spection of Man!   (Great applause.)
4823234823534848485348484848532349535353532353234848234853532353 
Astronomy.
27
LECTURE  V.
The PHYSICAL CONSTITUTION of our System....Discussion concerning the nature of Comets....Their motions
   --Their subjection to gravity... .Their immense periods... .Strange phenomena presented by Valley's Comet....
   Tke idea of Polarity, and its application to such phenomena....Probable universality of its developments among
   material phenomena.
  Ladies and Gentlemen : I have now endeav-
 ored to explain and fully to exemplify by means of
 the remarkable discoveries of the planet Neptune,
 the nature of the mechanism that sustains our Plan-
 etary System.  As we have seen it, it indeed ap-
 pears  most compact and harmonious—every orb
 bound to all others around it by sympathies which
 seem in dissoluble, and which raise the amallestatom
 from a condition of isolation into a constituent and
 eaaential part of the vast fabric. An understanding
 of this Mechanism, so full and minute as that which,
 under the guidance of Adams and Leverrier, has
 enabled us to penetrate with so sure an effort to
 the far region of Neptune, may well be considered
 at first sight almost to have exhausted all problems
 of interest connected with  our System; but inas-
 much as Man's knowledge never is nor can be com-
 plete—inasmuch aa it is his destiny always to strug-
 gle, and hia hope ever to riae—we have no eooner
 reached what aeems satisfactory in this line  of in-
 quiry, than doubts and  difficulties press  for notice
 which lead to investigations yet loftier and farther
 reaching.  It soon occurs to us, on  contemplating
 this  mechanism of ours,  that although the  law of
 gravitation entirely explains how it at present pro-
 ceeds,  enabling us to trace the many and complex
 relations of all these orbs, there still are facts con-
 nected with it, and these of highimport, which the
 simple action  of gravity as the sustaining  power
 does not explain.
  Nothing, I think, could convince one more surely
 than the discovery of  Neptune how completely
 we have got hold of the lawa governing the internal
mechaniBm of our system.
  I mentioned on a previous evening, for instance,
that we find  all  the planets  lying  nearly  in the
 same plane;  to  illustrate:   auppoae I  place a
ball  in the center of this  table; now let  the
ball represent the Sun, and then if I were to rep-
 resent the position of the planets by other balls, I
would have to place them on the table alao, and not
above nor below the surface of tbe table.   Now the
law of gravity does not explain this.  It would sus-
tain the motions of the planets round the Sun, how-
over lying in space.
  I also stated that the curve described by  an orb
revolving round the Sun is an ellipse, not an oval,
and that gravity would sustain a planet moving in
any ellipse whatever, but we find that these orbs
are all moving in an ellipse  very near a circle, so
near that  unless you represent  the orbit on a very
large scale you may represent it by a circle. Here,
then, ia another condition which the law of gravita-
tion does not explain.
  Thirdly: We find that the planets are all revolv-
ing round  the Sun in  one  direction. We do not
find one traveling in one direction and another pur-
suing an opposite  courae, but all [aweeping round
in the same  direction.  Thia also is quite unex-
plained by the law of gravitation.  They  might
move in any direction and still gravity would sus-
tain them.
  Fourthly:  We  find that the Satellites  move
round the primary planets  in the same direction
that tbe primary planets revolve round the Sun.
Now when we consider tbe number of the primary
planets, this may be regarded as a special arrange-
ment, and one not at all accounted for by the law
of gravity.
  Lastly: The planets and satellites have a rotary
motion on their axes,  as also has the Sun, which
completes its  revolution in twenty-five days, and
all these motions take place in the same direction.
This is not explained by the  gravitating power.
  Now when  persons look at these facts it must
strike them that there is some greatlaw here which
gravitation does not explain. I should mention, by-
the-by, that to the circumstances of  which I have
spoken there is one exception. The planet Uranus
has three satellites.  Herchel said it had six, but
no other Astronomer has ever been able to discern
more  than three.  Lord Rosse's great telescope
has never been turned  to Uranua, and the question
still remains  unsettled, but  we know tbat the
planet has three  Satellites.  Now in  this orb is the
exception.  Its  satellites are not moving  round
Uranus in the plane to which the other planets are
confined.  They  sweep out from it, nor do they
move in the same direction as  the other planets,
but in the opposite.  They move backward.  Now
this is the sole exception in  the whole  system  to
the order and the laws to which I have referred.
The planet Neptune confirms this order.   We now
know that Neptune has one  satellite, and its mo-
tion is the same as that of all the rest of the plan-
ets. I believe it may almost be said with confi-
dence that Neptune has two satellites.   A second
one, it is said, has been discovered by the excellent
telescope at the observatory at Harvard University,
but it has not yet been satisfactorily ascertained.
  The only exception,  then, is  Uranus, and the
question arises,  What are we to do with it ?  Are
we to accept this single exception as overthrowing
the general order? or as arising from aome  exter-
nal cause with which  we are not acquainted?   I
believe if you consider the  vast number of other
motions governed by the law to which I have refer-
red, you must consider the caae of Uranua aa an ex-
ception. If we had not treated the Comets so lightly
the other night I would say that a Comet would be
very acceptable  here.   [Laughter and  applause.]
  That these facts are constituent elements of our
System is not rendered necessary by what I have
termed the sustaining  power of Gravity, is suffi-
ciently manifested by the  phenomena of Comets,
for these wandering mists  pass round the Sun in
all directions and in the most elongated orbits, de-
fying every one of those laws which control the mo-
tions of ordinary planets.  Instead of being confined
to the plane traversed by the other orbs, they often
come moving up toward the Sun from all quarters
of the heavens.  Instead of moving in orbits nearly
circular, there is no ellipse so elongated that we do
not find Comets moving in it; nay,  we find them 
28
Prof. NichoVs  Lectures.
moving in orbits called parabola and  hyperbola, I
that is, in ellipses carried out indefinitely.  Comets
moving in such orbits visit our system but once, and
then plunging into tbe boundless confines of Space
are never more seen by Man.
  We know of several ellipses of immense exten
sion.   Halley's Comet has  a very elongated one,
stretching beyond the orbit of far-off Neptune, but
even that is near us compared with the orbits of
others we are able with great probability  to con-
jecture.  The great Comet of 1811—1 presume
many of my audience rememberit—regarded as the
most brilliant boBy that ever appeared in our heav-
ens, and answering to the most terrific de8criptiona
of the Cometa given by the ancients, seems to have
an orbit so immense that its period is  about 3,000
years.  To what an awful depth in space that body
must go no eye  but that of Omniscience can ever
discern, and yet there  is another whose orbit ap-
pears double  that of the Comet of 1811, its period
being about 7,000 years.
  The facts to which I have alluded, then, must be
held as  especially characterizing  the Planetary
System—setting it apart as a distinct and peculiar
arrangement, and no more flowing necessarily from
the connection of Gravity than the forms sustained
by the agency of life are sustained  by the energy
that keeps them in being.  Indeed, this illustration
is not inapt; for even aa Life diffuses warming and
glowing activity through  the whole innumerable
families of organization, so may this system of ours
be but one exhibition of what gravity can perform—
one special planetary arrangement, belonging only
to one special claaa, among the immenae varieties
which must roll around those myriads of single,
double, and more complex stars.
  Accepting, then, the circumstances  that I have
described,as indications ol the fundamental constitu-
tion of our aystem, the question arises, whence came
they ?  What new knowledge concerning the Uni-
verse do they communicate ?  It may, indeed, not
unnaturally occur, that questions like theae are  in
their nature unanswerable;  that they resemble the
inquiry, why is man's frame constituted as  it is ;
and that the only answer of which they are suscep-
tible, lies in the statement, " Thus was  formed our
system—thus fearfully and wonderfully was   it
made."  That singular collocation, it may be  said,
is inexplicable, because the planetary scheme ex-
isted simply as it now is, and  with  these arrange-
ments as its constitution, was launched into the do-
main of space by the immediate and direct fiat  of
the Almighty.  This, perhaps, is the most  natural
explanation of theae circumstances  one is  apt to
give ;  namely, that the system exists as it does be-
cause God has made it so to  exist. Now toward
that most dread of all mysteries—either the time
when  or the mode how—these arrays of finite
forms were projected from Himself by the unchang-
able Mind, I feel that I  dare not  approach,  and I
would venture to express  it  with  all  reverence,
that such an endeavor—one so utterly unfitted  for
the highest powers of Man, is imperatively forbid-
den by all philosophy.  Placed by the Eternal in
the midst of His gorgeous material Universe, we
are endowed with the  most glorious privilege to
look on Himself as mirrored there by the manner  of
His high-workings; but upon  the intellect  where-
with we must interpret these workings, He has laid
conditions that it must obey.  Now  one  of the
most indispensable of these conditions  is, that un-
less in cases where through a supension of the Nat-
ural Laws and other undeniable tokens, the great
Parent should choose to make manifeat His desire
and declare directly concerning His  purpoaeB, we
are bound by the necessities of our being to search
forth explanation of  every  physical part through
its relations with  actual causes present or past —
It is not given us to hope any where, or to  saj^that
we have known all; around us on every side is the
unfathomable, and the farther knowledge increases
the larger only grows that circle of darkness which
bounds ita light.  (Applause.)
  I would not be understood to say there was no
beginning.  Most undoubtedly there was—though
removed from us by infinite ages  that have rolled
away—guch a period; but to that period man  by
means of the faculties he now has cannot cenainly
go back.  Our knowledge of the 8olar  System,
with  its  characteristics seems to me something
like this :  If you present a blossom to the insect
called the Ephemera—which is born and dies with-
in the hour—if that creature could look understand-
ing^ upon that bloasom, it could aay thus was the
bloaaom  made;  but as to the  changes which
brought that blossom into existence, it could divine
nothing.  It could not reach the truth that the
blossom is the result of growth.  Just bo the Solar
Syatem lies before the  human mind.  We see an
external constitution, and we  are led to say with
the Ephemera, and with conclusion as legitimate,
thus and thus the system was made. We  are,
therefore, I say, bound to look upon that  mere ar-
rangement  as a circumstance wbich we must  at-
tempt to explain—whose  origiu we muat attempt
to discover in tbe mode by which the Solar System
arose out of a prior  syatem of being.  In all parts
of Physical Science the opposite course has  been
maintained.   Men have said, here you must stop.
Inquiry may not be extended  farther than this.
B ut I think it is the experience of all philosophy,
that in every instance  the barriers which have
been thrown up along the highway of Science by
bigotry and timidity have  been broken down.  As
far, indeed, as man sees amid this august immens-
ity, there is  no resting place—no barrier that he
cannot pass.   A traveler bold and free, amid a re-
gion thronged with  mighty mountains, he discerns
before him range behind  range in majestic pros-
pective, rising until vision cannot pursue them, and
they have hid their  summits within the clouds and
mists of the horizon; but  there, as his heart feels
full well—even there is concealment  only and no
termination ;  and ever and anon, aa the  ages roll.
that white cloud parts like the unfolding of a royal
gate, and lo! through  the opening, some noble
peak never seen by mortal eye, its top burning in
the Sun!—(Applause.)
   Again, pursuing inquiries touching Cosmogony,
peraons find many contradictions between their re-
sults and the results of the investigations of other
individuals, these contradictions have always been
brought  forward and insisted upon as  the ground
for stopping  inquiry in this  direction.  Now it
seems to me that we are never in a position to de-
cide when results do actually contradict one another.
The state in wbich Man seems to me to be placed,
in relation to all inquiries of this sort is the fol-
lowing :
       ^_JL^^           Man is here placed in a
     s*       *"x.        center  [A] of some sort,
   /            \^     & knowledge is stretch-
  /                \     ing out  all around  him.
  /       S' ~"\      \    Now within the compass
 I      f     \______1  q  of the small circle only,
 I      V.A  y      )    as represented in this di-
  V       ^~-S     I    agram, is his knowledge
  \                 /    complete—within  that
   \.             /     circle alone he is able to
     \-------*S       reconcile all the different
                         phenomena that present
themselves, and if he  goes beyond  that circle he
will find a  totally different condition.  Now some
bold inquirer, not satisfied with this limited range, 
Astronomy.
29
 steps out of the circle of clear and distinct knowl-
 edge, and pushes up to B, where he discovers a
 portion of truth, and he unfolds it.  Another bold
 inquirer strikes out in  a transverse direction, and
 pushes out to C, where he discovers a small portion
 of truth—or at  leaBt of what he thinka ia truth—
 also; but upon  comparison, our two inquirers dis-
 cover that their results  do not and will not harmo-
 nize. One canuot understand what the other has
 seen, and, forgetting that the vast space lying be-
 tween the two points of discovery, and which serves
 to connect them, still remains unexplored, one say a
 to his fellow laborer, "you muat throw away your
 fancied truth—it is an  error, it ia hereay."   The
 complaint of course, is immediately returned from
 the other side of the house, and they go on hurling
 their denunciations at  each other, 'till time,  at
 length ahowa  them that their  conduct is equally
 irrational on both Bides.  (Applause.)
   The sum of the matter, then seems to be  this—
 and assuredly it ought  never to be severed from
 the inquirer's mind: that now we aee only  a part
 —that a8 in the moral world, even in the wideat
 viewaof it upon earth, there  are many puzzling
 and painful contradictions.    So in  regard of that
 Mighty  Unknown which  environs all  our light.
 We  have distinct views only by snatches, views of
 parts only—between which and our  other con-
 quests, persistent darkness, notwithstanding our
 moat moat vigorous efforts, continues to reign ; and
 therefore, while holdingon in fullest confidence and
 faith never wavering, that we muat place the solu-
 tion of all difficulties in  the one caae and the  entire
 completion of knowledge in  the  other, among the
 hoped-for acquiaitiona belonging to thoae immense
 periods and serene realms which lie boyond the
 grave.  (Applause.)
   Having thus endeavored to clear our ground, so
 that no hidden scruple or reluctance shall interfere
 with our advance  in the course before us—I ask
 again whence thoae remarkable constituents of our
 Planetary System ?  Prom what prior condition,so
 that it obtain those constituents, must we imagine
 it evolved ? Bold inquiry truly for man to approach
 —but remember our illustration of the Ephemera !
 Remember how august  the processes we shall dare
 to  contemplate,  or awful the  depths  of Time
 through which we shall  track this growing order—
 we must compare them  never with Man's acts or
 life—they  are the ordinances of One  who  holds
 even the mountains in tbe hollow  of His hand, and
 before whose everlasting endurance the entire life
 time of the Human Race is only a tick of the clock
 wbich is heard and past forever!  (Applause.)
  The circumstance over which I am nosv to con-
 duct my bearers ia the moat sublime in the whole
 range of Aatronomy, and ia owing to the illustrious
 Laplace, who, perhaps, possessed a more profound
 knowledge of  the laws,  structure, and mechanism
 of our Syatem  than any  other aave NeWTON. La-
 place, upon observing  all of tbe orbs lying  in the
 same plain, moving in circles, sweeping round the
 Sun in the same direction, and next, that the satel-
 lites observed  tbe same directions, and finally, that
 the rotations of all the orbs proceeded in the same
 direction, at once said :  " This circumstance cannot
 be solved  by gravitation ; and there is only one
 mode by which  it  can  be solved, and  that is by
 tracing our scheme from its commencement through
 all  ita varioua stages of development up to this
 time." This is not an unusual thing in Science.—
 Geologists  do  not think they are doing an illegiti
 mate tbiog when they go back to  the origin  of our
 Earth and trace it from a liquid form to its solid
 Btate.  Laplace went a atep farther from this.—
 He said : " It is not improbable tbat all these orbs
came  into existence from a gaseous state, passing
from the gaseous to the liquid, and from the liquid
to the solid state."
  " Let it be supposed then," he said, " that this
great scheme of ours arose from the solidification
and gradual congregation of an immense Nebulous
mass existing in the aeriform or gaseous state."
  We know tbat matter does exist in this form.—
The Comets are gaseous bodies, and tbat immense
quantities of gaseous matter exiata, ia tbe moat im-
portant lesaon that tbey teach ua.  A8 many  as  a
million of Comets have visited our System,  and this
is few compared to the entire number that exiet,
therefore Laplace's supposition is not improbable.
  "Letus auppoae," Baid Laplace,  "in  the first
place, that our syatem arose from the solidification
of an immense Nebulous mass existiag in a gaseous
state."
  " Then," he said, "secondly : In what condition
must we suppose that Nebulous mass to have been
at the outset V   On looking at our Scheme he aaid,
"The most general fact that we can predicate in re-
Bpect of it ia revolution.   It seems  to be turning
round some great center."  •' Then," said Laplace,
" we can attribute to this Nebula motion of rotation
It must be  turning round a center  like  a great
whirlpool or whirlwind with a comparatively  slow
motion."  The  audience  will perceive tbat these
are two great hypotheses, but we muat begin with
hypothesea.  No calculation or deduction can ever
enable the human race to trace back our Syatem to
ita origin.  Thia being the caae I would have the
audience observe that Laplace's syatem rests en-
tirely upon hypothesis.  It is a hypothetical Cos-
mogony.
  Fancy, then, this great obscure chaotic masa ex-
isting of old amid the void, even where our auperb
Syatem unfolds  its glories—agitated  by some mo-
tion which approached to a definite rotation; now,
quitting all hypotheaia, let us Bpply to it the super-
vision of Law and endeavor to follow its destinies.
  All that is hypothetical I have already men-
tioned.  What follows, is the application of known
mechanical laws.
  Let ua now imagine an immense Nebular mass
from which our  System sprung,  situated in space,
with all its parts gradually drawing toward a cen-
ter.  You recollect we aupposed this mass  original-
ly to be moving round that center with a motion
extremely slow:  What will result from this mo-
tion of rotation in consequence of the  condensation
of the Nebula?   This follows.  Ever as the Nebula
condenses, the  motion of rotation  will  become
quicker and quicker, and finally will present itself
under the aspect of a very definite  and majestic
phenomenon. I think tbe audience will  Bee that
this will be the case.  Tbe entire masa ia aupposed
to be turning round all the while, and the particles
moving toward the center at the same time.  Now
it is obvious that a particle at the circumference of
this mass will move much more swiftly than one at
the centre, and  when a particle from the circum-
ference goes down to the center, as is continually
happening, it attaches  itself to a center particle
and of course communicates to the particle so at-
tached a portion of its velocitv,  wbich must inevi-
tably increase the rapidity of the particle at tbe
center.  Thia may  seem abstruse but there are
plenty of phenomena in every-day life to illustrate
it.  We will take  the pendulum to a clock for in-
stance.  Suppose the clock moves too slow, what
doyoudo? Shorten the pendulum of course. Now
it is thia very principle that will cause what I have
been describing. It will be seen then tbat as this
matter draws itself toward the center its motion
becomes swifter, and tbat the body formed will have
a rotation upon  its axis.
  Thus the great fact of the Sun's rotation is neces- 
30
Prof. Nichol's  Lectures.
 sarily inherent in our hypothesis, but does the hy-
 pothesis cod tain what seems far more difficult to
 conceive—the origin of theae planets.  So far we
 have spoken of nothing  but thia huge  mass—no
 planets.  Letusseeif in accordance with a clear
 and distinct law, planets can arise from this mass.
 What gives the outer portion of this Nebula any
 connection with the center of the mass? Every
 particle on the outside of this Nebulous mass is act
 ed on by two tendencies  precisely similar to those
 which regulate the motions of the planets round the
 Sun; first, its tendency to fly away in consequence
 of its motion, and secondly, the  attraction exerted
 over it by the whole mass which counteracts  this
 center-flying tendency.  Suppose howeverthatone
 of these tendencies increases while the other does
 not.  Suppose, for  instance, that  tbe tendency of
 the outer portion to fly away increases while the
 attractive power remains the same: what will take
 place ?   A separation of the mass, undoubtedly.—
 We know that the matter all around us upon tbe
 Earth is not homogeneous.  There  are varieties in
 it. We would naturally suppose therefore that the
 Nebulous mass out of which these orbs are passing
 would exhibit the same varieties of matter.  If this
 were the case at intervals, the leastcondensive por-
 tions would gradually accumulate at the outer part
 of the Nebula.  Suppose this  to have  been done
 then, bo that at the outer portion of this Nebula
 there is a quantity of matter not bo easily condensed
 as that  occupying the inner portion.  Now this in-
 ner portion would go on condensing more and more
 rapidly, and in consequence of this condensation
 the outer portion of  the Nebula would be moving
 more swiftly, the equilibrium would be broken, the
 power drawing the outer part toward  the center
 would not be so great as its tendency to fly away.
 There would then occur a separation between the
 outer portion of this mass—it would spread into a
 kind of  ring standing by itself.   This also may be
 illustrated by a common occurrence.  For instance,
 sometimes when a grindstone  is turned  with too
 great velocity the outer part of it flies off.  Now if
 this outer portion had not  been solid stone  it would
 not have broken. Had it been a band of caoutchouc
 for example, it would have stood out,  a ring.—
 Now this would  be precisely similar to the action
 of the mass to which I have referred. There would
 then occur, during the condensation of this Nebula,
 if it were not composed of homogeneous  matters,
 ever and anon a throwing off of a ring which would
 lie out  by itself in space.  We  here, therefore,
 have  an idea how dependent matter would arise in
 the condensation.  Indeed the ultimate  state into
 which this condensation  might bring this Nebula
 would be as follows:
   We would have a large orb in tbe center, and at
 different distances  in space  apart  from  it, there
 would have been thrown off from it these depend-
 ent rings, turning round the central mass of course
 with the velocity with which the whole mass turned
 when they were thrown  off.  We thua have, aa
 our first step, a great central orb and dependent
 rings  lying out from it entirely in  space.  Now,
 before proceeding farther—before inquiring what
 forms of matter might probably spring from theae
 rings, 1  would solicit my audience to observe what
 already  we are able  to deduce.
  We can draw two  inferences.  Whatever the
 forms of theae  rings, they must  be lying in the
 same plane.  Then again  observe another fact
 lhe  rings, as  I  have stated already,  are found
necessarily turning round  the Sun with the velocity
they had when thrown off, and they muat all turn
in the same direction.  Then again, whatever ia to
come of  theae rings—whatever shape they aasume
the great chance is that  this  kind of matter will
turn round the central mass almost in circles. Now,
then, observe as far as we have yet gone, the moat
important of these constituent points have been
explained:
  First—That  all the planets are lying  in  the
same plane.
  Secondly—They  are  all turning in the same
direction.
  Thirdly—Their orbits are nearly circles.
  As we proceed, the problem is manifestly becom-
ing simplified—we are rapidly absorbing within
one hypothesis all that seemed previously unintel-
ligible.   Let us advance with equal caution another
step, and ask  what is likely to become of thoae
rings?  In what manner  will their particles ulti-
mately  arrange themselves?   Now,  first: if  the
ring, when it was thrown off, had been homogene-
ous and of the same thickness, or if during its sub-
sequent changes, had been subjected to no foreign
influence, the ring would solidify and remain as a
ring; but if it were not homogeneous, and of the
same thickness, or if it had been subjected to  for-
eign influence, in consequence of its not being uni-
form the  power of attraction prevailing in itself
would break it up.  Now.,  it ia possible—although
extremely improbable—that the ring would aolidify
and remain permanently as a ring in space.  We
might, therefore, considering tbe great number of
bodies in our System, expect to  find some one f
them accompanied by such a formation,  and anr
enough we have one instance of the whole matter
solidifying itself and remaining fixed in the heav-
ens, a ring.  Saturn furnishes us with this instance,
which is the only one in our System.   It has been
aaid that Neptune has a ring, but I think adelnsion
has existed in  this regard. It was formerly sup-
posed that Uranus had rings, but it is now known
that such is not the fact.  In all probability, then,
the ring upon Saturn is the only one in our Syatem.
I beg the audience to remember what I  aaid con-
cerning this  matter.  I said such a formation wag
possible  but highly uncertain; and the bringing
this ring into our System  is a confirmation of our
theory.  When we are able to summon forth such
formations to explain what is called an anomaly 01
a monster, we may be pretty sure that we are ar-
riving at the truth.  They  stand out aa finger posts
to direct the attention to the inveatigation of  the
causes that produced them.  (Applause.)
  Secondly: Suppoae the  ring not to be uniform,
as is by far the most likely to be  the  caae. Sup-
poae, for instance, that it had in different parts of
it denser portions than in other parts, then the re-
sult would be this: Around theae denser portions
the whole matter would, ultimately, congregate.—
It would cease to be a ring, and by the greater at-
traction of these denser  parts tbe matter of the
ring would be drawn around them.  Now suppoae
these denser portions were scattered  through the
ring in such a way that their attractions would
exactly balance each othpr.   If the  points acted
so as to  produce equilibrium, the ring  would be
broken up into a number of bodies, and they would
appear as a  number of small orbs revolving around
the Sun at nearly the same distance. Accordinglyi
just  as  with  the ring of  Saturn, we have also
one instance in our System of just such a reault as
this, viz : that group of small pianets lying between
Mars and Jupiter, all revolving in nearly tbe same
orbit.  We formerly supposed there were but four
of these  Asteroides;  now,  however, we know
there are eight, and there may be more.  Thui
you perceive we have drawn  into our Syatem order
out of disorder.
  The third mode in which the ring might resolve
itself is by far  the  moat  probable; it would  con-
dense and splitup but the parts into which it would, 
Astronomy.
31
 in that case, be divided would not balance each
 other, but one part would be greater than the oth-
 ers and the large part would absorb all the  others
 so that the main result  would be tbe breaking up
 of the rings  into separate large planets.  These
 planets would in the course of their condensation in
 order to form solid bodies, as it were, pass through
 something of the same course as the original masa,
 throwing off satellites characterized by the same
 conditions  as themselves.  Here then you see the
 Nebular hypothesis has  given us an entire account
 of the structure of our system and the characters
 of the bodies of which  it is  composed.  Another
 thing alone remains, viz; the rotation of the bodiea
 upon their axes.  This  point I think my audience
 will readily apprehend.   The question is, how does
 it happen that these bodies are moving round their
 orbits?   Let us go back to  the original Nebular
 mass.  It will be remembered that the particles of
 the inner portions of the mass are not moving as
 fast as the particles of the outer portions, so that
 the instant the mass is broken, the stronger action
 of the outer portion would prevail over the velo-
 city of the particles of  the  inner  portion  and
 cause the  bodies to  go round just in the same
 direction aa  the orb moves  in  its orbit.   This,
 also, is illustrated  by  the most common things.
 Suppose  for instance, that in  the case of the frac-
 ture of the grindstone referred to, we  observe the
 portions  as they fly off.   We would find  that the
 fragments would turn round in the air in the same
 direction as the grindstone itself turns.  This, then,
 is tbe last of the conditions to which I have referred;
 and it receives, I hope, a complete and satisfactory
 explanation from this hypothesis of Laplace.  We
 have now a reason why  our system presents itself
 not as an original, created and  finished  scheme,
 but as growing from a previous state.
   How strange the thouehts with which in pre-
 sence of the speculation  I have now endeavored to
 unfold, we must gaze on the brilliant skies!—even
 that gorgeous jewelry of midnight, a birth—a thing
 of yesterday—a step in  the  awful march of those
 visible picturings  of the purpose of the  Eternal
 Spirit! Realize,  in illuatration, for one moment,
 the position of the tenant of a hut on the banks of
 the mighty Amazon at one of its great bendings;
 tell him that the waters  whose opposite  bank hia
 viaion can scarce reach,  are not  an immense lake
 with appointed boundaries, but that  born of rills
 among moutains that are unseen and ever increas-
 ing in depth  and potency, they  have rolled  down-
 ward until a whole  continent is  passed, and then
 mingle and  lose themselves with an ocean engird-
 ling the wide  earth with  its everlasting waves ; so
 in the view of these  high cosmogoniea, seem  to roll
 on thoae  gorgeoua Stellar Developments, whose
 limita no eye can now see—sinking among the vast
 depths of  time, in some  hidden purpose of God—
 roliinar onward as the ages flow, and augmenting,
 like the mighty river, until the boundary of Time is
 reached, and their course ends among the Q-uietudes
 of Eternity.  (Great  applause.)
   One farther point only we require to establsfe,
 ere this similitude be complete.   As  the  great
 System before  us had a birth and a progress—a
 growth toward its present glory—can we stretch
 onward our gaze toward a time when its strength
 shall wane—toward  the  closing  scenes of  these
 stupendous arrangements!
  Even so, this Nebular  hypothesis leads us to a
 glimpse of this change, it carries us onward to the
 time when our system shall cease to exist as it is,
 and pass into some other  form  of being.  The cir-
cumstances attending this change appear to be the
following.  Recollect the  two influences that keep
the planets in their  places.   Suppose anything |
 should operate upon Jupiter to retard its progress
 and diminish ita centrifugal force.   It would neces-
 sarily be drawn into the Sun.  Now  the tendency
 of Jupiter or any other planet to fly away from the
 Sun might be constantly retarded  by some  such
 action  as this.   Suppose  that these planetary
 spaces  are not void, but filled with  ether, the mat-
 ter out  of which  these bodies sprung.  However
 light, the fact that all the planets are required to
 mcve through that ether must subject them to con-
 stant retardations.   If,  then,  this  ether exists
 throughout  these planetary spaces, every planet
 moving through it must be subjected to its resist-
 ing power, and as the orb  cannot put forth any
 vital power to overcome  it, it must  continue for
 ages and ages to retard its  motion.  Now the re-
 tardation of the motion diminishes the planef s ten-
 dency to fly away from the Sun, and, consequently,
 the attraction of the Sun will cause it constantly to
 approach nearer and nearer that orb, till it last it
 will be absorbed by it. Now, it might be suppoaed,
 that if this ether exists, we should with our fane in-
 struments discern ita effects  precisely in this  con-
 nection, and that we should discern  how much it
 retards the planets—how much in every revolution
 the planet is drawing nearer and nearer to the Sun.
 But alas ! the  planets are by far too heavy to be
 subject to a perceptible retardation by so subtle an
 agent.  What the planets nave aot enabled  us to
 accomplish, however, has been done by means of a
 Comet.   It  was accomplished by the Comet of
 Encke, which revolveB round our  Sun in  three
 years,  pasaing through the orbita of some of oar
 planets.  Now the Comet and the planet stand in
 relation to each other in thia wise:  Take a piece of
 metal and a feather; drop them ; the metal falla at
 once to the ground—it meets with no perceptible
 retardation;  but the feather  moves about in the air,
 seeming as though it would never reach the ground.
 Thus the feather showa us  what the metal would
 not—that if one suffers retardation bo must the oth-
 er, although too small to be appreciated. Encke's
 Comet is the feather, and the planet's the metal.—
 Thus the Comet has demonstrated this fact so that
 AstroDomerB acknowledge it; viz ; That there is a
 planetary ether filling the spaces between the orbs
 of our System,  Every time this Comet returns it
 is retarded about two days, so that, in time, it will
 entirely disappear.   Now the influence exerted
 upon this Comet must befal the planets, and though
 ages so vast must roll on that  one  may call  them
 infinite, these solid orbs must be retarded, drawn
 nearer and nearer to the center of the System and
 thus our vast planetary scheme pass into another
 mode of being.
   Thus  the Nebular hypothesis shows us, not only
 the origin of our system, but carries us onwards to
 the time when it shall undergo aome great organic
 change.  Thia will not take place, however, as was
 supposed in the  earlier stages of Astronomy, by
 violence.  It was once anppoaed that the pertur-
 bations  of the planets, would grow ao large as to
 interfere with tbe order of the system.  But this is
 not so.   Ihe  perturbations  exactly  balanee each
 other, and from  this  source  nothing like confusion
 or ruin can ensue.  Neither will there be confusion
 from that which I have just unfolded.  Not in con-
 fusion shall this magnificent scheme finally pass
 away, not with the jar and confused  voice of ruin
 but even in its own quiet aud mejestical order, like
 the flower, which having adorned a speck of  earth
 lets drop its leaves when its work is done, and falls
 back obediently upon its  mother's bosom!  (Ap-
plause.)
  It may still be in the recollection  of some of my
bearers, that I presented in our second lecture an
exhibition of the nature of the activities prevailing 
32
Prof. NichoVs  Lectures.
through all these Stellar Hosts—how, wherever
such orbs are, there is change—immense motions
accomplishing majestic purposes—all thingsrush-
ing on toward some new  condition—proclaiming
that  evolution, ceaseless and irresistible—advanc-
ing from tbe imperfect to tbe perfect is the Law of
the Universe.  That, indeed, was a noble specta-
cle—myriads of  Suns in gorgeous  arrangement
marching onward, each  on its great way, pointing
toward  regions far beyond  the sight; but with a
significance bow much more  profound is this same
lofty truth when once more declared.  The develop-
ment of which I there spoke, was only an altera-
tion in internal distribution of groups of stars, pro-
ducing a change and gradual perfecting or simplify-
ing of external form: but now we discern the orbs
themselves  rising,  enduring, and  then  melting
away; even these most stupendous manifestations
of a material organization undergoing in their in-
most structure the doom of mutability, bowing be-
fore that profound Law which persists or eminent
ly endures  as tbe  cause  and  substratum  of all
change!  How overwhelming must be  those pur-
poses whose greatness even these Heavens are not
adequate to  represent—whose amplitude, even
these  unfathomable  depths  cannot  contain—of
whose purity and expanae  that whole Univerae of
stars is fitted to be an emblem only so transient!
  There, a mere speck in the void, yet of itself bo
complex, so perfect, so grand, floats that Solar Syt.
tem of which our varied and beauteous world is but
a minor part—it is but as a blossom fitted for a mo-
ment only to unfold itself and live, as tbe seasons of
the august  Universe pass.  What, then,  is this
scheme as a whole ?—where its beginning?—where
its end?—and  what  the  solemn Forms of which
theae existing splendors are but tbe early and im-
perfect rudiments ?  Questions, indeed, most vain!
never, it may be, to be resolved by any whose ten-
ement is in the flesh!  And yet  not vain in thii.
Tbey seem to  tell of that light which shall pour
through the opening of yonder portals—sbadowi
cast toward Earth by Alpine heights of thought-
inaccessible now, but into whoae presence anon, at
a reverent child, the soul shall come, at that dread
but not fearful moment, when, amid the crash of
worlds, the meaning  of the Phantasma shall all be
revealed—the awful vail being rent in twain. 
Astronomy.
33
                                     LECTURE VI.


Constitution of the PLANETS rapidly reviewed___Constitution of the MOON___Prevalence there of the cause
   which has upheaved our Earth's surface....Universality of tbis cause___Its nature, as indicated by tbe aspect of
   the Moon, not comprehended within cunent geological theories___Its tremendous craters or caverns.... Wh.t gave
   existence to these:. ...Speculations us to this force.... Two opposite views of it___Digre«sion concerning meteoric
   stones---Progress of this grand cause of u pheaval---Possibility of a relation between it and the apparition of the
   organic families on the surface of the Earih.
  Ladies and  Gentlemen :  I now proceed with
you  to  the last portion of those  contemplations
which I desired to bring under  your notice.  We
have spoken of the general structure and apparent
destinies alike of the remote  heavens and  of our
own Planetary Scheme; and I wish now to offeryou
a few thoughts  on such details  in regard  of tbe
constitution of our Companion Orbs, aa more espe-
cially manifest their connection, as derived, proba-
bly, from a common origin.
  Notwithstanding  the memorable power of the
Telescope, the information we have obtained in re-
gard to tbe internal constitutions of the  planets, is
indeed singularly scant. I am not sure, indeed,
that we can venture to state farther in  regard  of
them than two very general propositions.   The
-first is, that in so far as we know aught concerning
tbe Primary Planets, matter  exists there  in the
same three normal conditions as we find it existing
on the Earth, viz .- in the solid, the liquid and the
aeriform or gaseous states.  These orbs  have,  aa
far aa we know, atmospheres;  and we discern
floating aboutin these atmospheres clouds, clearly
indicating that there  is developed in  them matter
in a liquid state, so that the inference ia  that their
physical constitution is in every  respect similar to
that of ourown Earth.   There is one important ex-
ception to this, however, which  we are  certain is
manifested by one orb and which may characterize
all tbe Secondary Planets. This exception occurs in
the Moon. In tbe Moon we find matter in the form of
air.  The Moon has an atmosphere, though a small
one.  There are many doubts concerning an atmo-
sphere in the Moon, but I think, however, that the
phenomena which have been observed during So-
lar eclipses go to show that it has  an atmosphere.
Matter in the liquid  form, however, does not exist
on the Moon.  There is no water in this Luminary
and never has been any, a truth which we shall  be
able to establish in the course of the lecture.  The
mode in which we ascertain the absence of water
in the Moon is very simple and accurate.  It is  as
follows:  As we can trace the Moon through all its
phases, we may also  trace the line of increasing or
roaming light, which  is the  line of the beginning of
morning or the close  of evening, across every por-
tion of its surface.  Now if that light passed across
an ocean or great lake or any collection of liquid, we
would find, asis the case when our own Oceania the
horizon, that it would be an even line unmarked by
any ruggednesses,but on the contrary this lineisrug-
ged everywhere, arising from the shadows cast by
irregularities in the ground across which it stretch-
es.   Tbe Moon, indeed, has  comparative flat places,
such as  those  dark  spots marked on  the  map,
easily seen on the Moon's surface with a good tele-
scope, but even there the ground is undulating and
quite unlike any collection of water.
  The second truth,  however, is much  more im-
portant and contains that to which,  more  especially
this evening, I would solicit your attention.
  The following fact appears to be universal.  We
 discern it in all tbe  planets which we have  been
 able to examine-  It ia this: the aurfacea of these
 orba are  broken and irregular,  like the surface of
 the Earth.  In other words we find  there moun-
 tains, continents, oceans, great valleys and irregu-
 larities of every description which we find on the
 Earth.  The Moon is an especial example of this.
 In most other planets mountains are discerned, and
 in some of them, such  as  Mars, we see even the
 division into continent and ocean.  While acknow-
 ledging the importance of this  fact, however, I do
 not deem that the simple discovery of what modes
 and disposition of land and water, of ocean and con-
 tinent are manifested by the surface of any of these
 globes, is  that which  ought most  to  attract us
 during the examination; we propose, nay, we can-
 not regard these  modifications  aright, as we find
 them in Mara, Venus, and tbe Moon, unless the
 grand and singular fact be retained in the memory,
 that the phenomenon is a Cosmical and Universal
 one; and that whatever the cause which has up-
 heaved  the surface of these  orbs, it has acted
 throughout all the domain  of the Planetary System
 and left  its mark  on the  face  of every body yet
 explored by the Telescope.
   Regarding the subject, then, in this ita real gen-
 erality, we cannot avoid the conclusion that if the
 Science of Geology shall ever succeed in discerning
 the source of the influence that has thus diffused its
 results ao widely, we ought through this its grand
 generalization to explain  satisfactorily not merely
 the form and phenomena of upheavals  as they are
 developed on the Earth, but likewise all similar
 aapects recognizable among our Companion Planets;
 or if expectation bo high  is too ambitious for tbe
 present condition of Geological  Science to account
 it hopeful, there is still in tbe truths revealed by
 these foreign bodies, much wherewithal we may
 correct premature  or special conclusions, and by
 whose aid we may avoid the hazard  of accepting
ias an universal law what  is a simple result of cir-
 cumstances that have no  universality  but belong
 rather to the conatitution and specialty of the par-
 ticular orb we examine.
   Tbe great value of our looking at the Moon and
 these otber bodies in this  point of view is tbat it
 will enable us to relieve  our theories  concerning
 the structure of the Earth from  all mere specialty.
 It is with this view then, and not merely to gratify
 curioaity by an inspection ofiaolated wonders, that
 to night I solicit you to  review  the appearance of
 the Moon—a planet which of  all others is  most
 within our reach  and  connected with which we
 find almost every conceivable facility for clear and
 little-interrupted inspection.
   The Moon, of all other bodies, is situated so that
 we can obtain tbe most favorable view of it  with
 the Telescope.  In the first  place the entire ab-
 sence of water causes  the absence of clouds, hence
 the surface is never tinged  with obscurity,  or  if
 tinged at all, only  obacured in  consequence of tho
 mist floating  in  our own atmosphere.  All the 
34
Prof. Nichol's Lectures.
 other planets are more or less obscured  by clouds
 floating in their atmospheres.  Venus, for instance,
 although so near ua, haa such a heavy atmosphere
 constantly surcharged with clouds that our knowl-
 edge of the orb  is doubtful;  while Mars, although
 much farther from the Earth, is, owing to the va-
 riety of  its  atmosphere  and  its freedom  from
 clouds, seen with singular distinctness. The Moon,
 as before remarked, having none of these obstruc-
 tions, appears clear and  distinct. Beside, it is com-
 paratively very near the Earth—being only 240,000
 miles from  us,  a  distance which, astronomically
 speaking, is but a  mere unit.  Now taking into
 account what the Telescope can do, the Moon is
 brought very near us. A nine-inch Telescope, with
 a magnifying power of a thousand times which I
 for some time used,  brought, as you can readily
 calculate, the orb  within two hundred  and forty
 miles of me.  A  Telescope with a magnifying
 power of three thousand times would bring it with-
 in eighty miles, and by  applying  a  power of ten
 thousand, which might be done  under favorable
 circumstances, this  Luminary  would be brought
 within  the small  distance of  twenty four miles !
 The audience muat not compare observing  the
 Moon at this distance of twenty-four  miles with
 viewing  an  object located on the Earth,  at  the
 same distance, for the view of the Earthly object
 would  be obstructed by tbe lowest and densest
 portion of our atmosphere ;  but it  should be com-
 pared with the view we would have  of  an  object
 situated directly above ua  at the higbt of twenty
 four miles, when the vision would be much less
 affected  by  the  atmosphere intervening,  as  it
 would be of  the the clearest and  best quality.   I
 hope the audience  will not take such a view of tbe
 matter  aa a gentleman  did who  on hearing me
 state that we could go within eighty  miles  of the
 Moon, waited on me afterward in troubled wonder,
 asking why we did not akip over tbe intervening
 space and go out to it altogether ?   (Laughter.)
   Such are the circumatancea with which we  ap-
 proach the examination  of  the  Moon. In  posses-
 sion of these facilities, then, and with the foregoing
 object in view, let  us examine with  attention the
 up heavals which this globe [the Moon]  presents :
 and we find them divided into three distinct classes
 or  orders.
 '  1 will juat mention shortly,  before proceeding to
 tbe description of these  mountains, the means by
 which we ascertain their character and  elevation.
 This ia effected by measuring the shadows cast by
 them upon the Moon's surface.  To illustrate:  You
 observe that this pitcher casts a shadow of a cer-
 tain length.  Now  as I raise tbis light the shadow
 grows leas and less, till at length you perceive tbat,
 as the light arrives exactly over the object, it casts
 no shadow at all, and as the light continues to pass
 on the Bhadow begins to  appear on  the opposite
 side of the pitcher, and it  continues to grow  longer
 and longer as tbe light descends. We observe the
 relative positions of the  Suu and the Earth.   We
 mark the extremities of the long deep shadows cast
 by those elevations on tbe Moon's surface, and we
 find tbat as tbe Sun mounts higher and  higher in
 the heavens,  these shadows gradually recede to-
 ward the bases of  tbe mountains: and when the
 Sun arrives at the zenith tbe ahadowa entirely dis-
 appear; but by-and-by, aa our majestic Luminary
 sinks to his bed in the West, the  shadows come
 creeping out on the opposite side of the elevations,
 and we, by watching thus  their movements, are
 enabled to ascertain  with mathematical  accuracy
the character and bight of these Lunar mountains.
There is no exaggeration in respect to our ability
to measure bigbts and distances on the Moon. The
shadows on the Moon are not like shadows on the
  Earth.  They are black as midnight, and as clearly
  defined as form can be.  Thus  are these results re-
  liable, and  in truth we are at present better ac-
  quainted with the structure of one side of the Moon
  than with any hemisphere of our own globe.
    There  are  three classes  of Lunar  mountains.—
  The first class  consists of isolated, separate, dis-
  tinct mountains of a very curious character.  The
  diatinguiahing characteristic of these mountains is
  this:  they  start up from a plain quite suddenly.—
  On the Earth, it is well known that mountains gen-
  erally go in ranges or  groups,  but we find  these
  isolated Lunar mountains standing up entirely apart
  —never haviDg been connected with any range.—
  Here is one [the lecturer here pointed to a splendid
  telescopic map of the Moon] named Pico, which  is
  9,000  feet high.  This mountain has the form of an
  immense sugar-loaf; and if the audience can ima-
  gine a fairly-proportioned sngar-loaf  9,000 feet in
  hight, and themselves situated above  it so as to be
  able to look down upon its apex, they will have an
  approximate  idea of the appearance of Pico. There
  are many other mountains of a similar description
  scattered over the Moon's surface, and these moun-
  tains not only stand apart  from  each other, but,
  what ia atill more remarkable, the plains on which
  they stand  are but slightly disturbed.   How singu-
  lar, then, the influence that shot these mountains
  up 9,000 feet and yet scarcely disturbed the plain
  in their immediate neighborhood.
    The second class of Lunar elevations consists of
  mountain ranges.  Now thia is the principal fea-
  ture of the mountains upon Earth. They are rarely
  found associated in any other manner  than in vast
  ranges.  This phenomenon  is  also found in the
  Moon, but there it is the exception; only two prin-
  cipal ranges are found and  these appear to have
  been originally one range.
    One is called tbe Appenines.  It is  so well seen
  that just as the line of light is passing through the
  Moon  you will think it is,  generally speaking,  a
  crack in its surface, but a telescope of ordinary
  power will  at once manifest it to  be a range of
  mountains.  Now the  Lunar Appenines  may be
  compared with  the.loftiest  ranges of mountains
  upon Earth.  It is 18,000 feet high,  and  there is
  another range still higher—risirg 25,000 feet above
  its  base.  In this  feature, then, the  Moon corres-
  ponds with the Earth, but with  this  difference.—
  Wbat is the rule on the Earth  is the exception on
  the Moon.
    There is, however, another very remarkable fea-
  ture in which these ranges in the Moon correspond
  with Terrestial ranges.  We find that on one side
  the mountains are quite steep, descending  precipi-
tously, while on the other side they slope away
  through an extensive highland.  Now this very re-
  markable law holds also with respect to ourTerres-
  tial ranges.  It is not universal but is so general that
  some of our Geologists have aa8umeditaa mainly in-
  dicative of the cauae that has up-heaved our moun-
  taina.  The Himmalay a mountains present this fea-
  ture most strikingly.  On the South side they are
  bold and precipitous, while on the  North  they
  shelve gradually away, extending in picturesque
  grandeur over many a mile of mingled mountain,
  valley, gentle declivity and rolling plain, till at last
  they slope gently down and are lost in the level
  earth. So, too, the Andes exhibit this feature. It  is
  a  fact  too remarkable to be considered accidental,
  and assuredly the cause which produced  it upon
  the earth  Earth must be similar in Nature to  what
  evolved it in the Moon.  Now our physical Geogra-
phers have usually been disposed to attribute tbe
Terrestial phenomenon to the action of great floods
or currents of water originating in different ways.
And it seems no inadequate illustration of the ben- 
Astronomy.
35
 efit which Astronomical observations might bestow
 upon Geology that the Moon negatives tbis expla-
 nation at once, for on tbis orb, as we have said, no
 liquid exists and has never been.
   But the prevalent form of elevation belongs to
 neither class.  At least two-fifths of the surface of
 our Luminary are studded with  profound caverns
 penetrating its body, and generally  engirt at the
 top by a great wall of rock which is surmounted or
 crowned by lofty peaks.  These caverns, or, as they
 have been termed,  craters, vary in  diameter from
 fifty to sixty miles to the smallest space visible,
 probably one hundred and fifty feet; andthenum-
 bers increase a8  the distance diminishes, so that the
 multitute of the small ones passes enumeration.
   In order to impress upon you what these objects
 are let us pay a visit to one of them, say the crater
 of Tycho.  As we approach the crater we will find
 a very rough country. Our first  glance would  be
 arrested by a wall of solid rock  appearing in the
 horizon stretching fifty miles away. As we ap-
 proach we will find this wall sloping up to the hight
 of about 3,000 feet.  Suppose we ascend.  What do
 we expect to see on the  other side—a slope ?  On
 the contrary, when we arrive at  the top,  we find
 ourselves on the brink of a precipice tbat in one leap
 goes down 13,000 feet!   Then we discover below
 that enormous depth some similar ranges of moun
 tains, lying like terraces and atretching round the
 base of the wall, and a little onward beyond these
 lies the bottom of the chasm which is  17,000 feet
 from where we stand.  The diameter of the cavern
 is about fifty-five  miles.  If a person were standing
 down in its center he would see  on every side, at
 a distance of twenty-five miles, an appalling preci-
 pice rising up 17,000 feet—2,000  feet higher  than
 Mont Blanc.  If  there are  any inhabitants there
 they must have  some means of locomotion  with
 which we  are unacquainted.  (Laughter and ap
 plauae.)
   Such then is Tycho, and precisely of this  kind
 are all the craters in the Moon.  Many of them are
 not so  de,ep, some of them  nre deeper.   Some in
 the southern part of the  Moon are  said to be  so
 deep that we can never see the bottom.  Whether
 this be so  or not  there are several 3,000 feet  in
 diameter and as deep as Tycho.
  Now it is evident on the very first glance that
 even our largest volcanic craters are not to be com-
 pared with theae caverns of the Moon.  The largest
 we have any knowledge of is in the South Sea Isl-
 ands, but that ia comparatively small and is situa-
 ted at the top of a mountain.  In order  to discern
 asght similar upon the Earth, then, we must  look
 to larger displays  of the disrupting energy.
  [Tbe Lecturer here drew a diagram of a group
 of mountains among the Alps, exhibiting  the cir-
 cular formation but differing from Lunar  Craters
 in two  points.  In the first place the range is bro-
 ken by gaps; and secondly,  the interior is not a
 pit, but, on the contrary, rather higher than the ex-
 ternal surface of the Earth.   He ahowed then how
 these might be explained by the presence of the
 meteorological agents—rain, frost, wind.  etc.—on
 the Earth, which are not present in the Moon:  and
 interpreting them  by tbis  principle it seemed that
 the older of our terrestial mountain formations  ren-
 dered it likely that the crater form did, in the  ear
 Her epochs of the Earth's geological history, prevail
 likewise here.]
  May it not then be that the Moon is simply in a
 comparatively early epoch of its  developement ?
 That, as the Nebular hypothesis  would seem to
 establish, tbe Lunar globe  is younger than  the
 Earth;  and that with regard to it, also, a time may
come when the upheaving cause will manifest itself
principally,—as now in the Earth—by upheaving
 ranges and groups of mountains instead of craters ?
 This is probably all that we can derive from a view
 of this portion of the subject.
   To proceed with our  subject, can we  form  any
 idea regarding the nature of the power which could
 produce craters like Tycho ?   There is  a feature
 connected with this crater which,  in this respect,
 is of high importance.  I mean thoae broad  bands
 which iaaue from it and go across the surface of the
 Moon even to the distance, in one caae at least, of
 1,700 miles.  [The Lecturer here went through a
 minute investigation of the characteristics of these
 bands,  chiefly by means of diagrams on the black-
 board, and elaborate paintings, which we regret we
 cannot give. He seemed to render  it probable
 tbat, like our own trap-dykes,  these bands consiaS
 of matter which must have come up from the inte-
 rior of the Moon's mass through cracks in its solid
 crust.  Now as these  cracks must  have  been
 formed by the convulsion which produced Tycho,
 this convulsion,  then, must have  been sudden as
 well as most violent, at once producing the cavern
 itself  and cracking  the  Moon in the manner in
 which we see it. The phenonema here indeed
 cannot be reconciled to  any gradual operation or
 the action of any  force  long continued.  It must
 have been as sharp aa violent;  instantaneous after
 the manner of an explosion.  Tbe imagination,
 habituated to tbe comparative quiet of  our time,
 cannot easily reach the conception of a convulsion
 like this.  Let my audience  not discredit or doubt
 the speculation because of the fancied oddness or
 the gigantic character of the force whose action it
 presumes.  So far from being impossible, the  like
 ofit, in part at least, has passed during the  pro-
 gress of time in almost every region  of our  globe.
 It ia clear and  perfectly indisputable, tbat when
 our own  granitic  ranges  were pushed  from the
 Earth's interior they bore  up along with them
 many miles of rock of vast thickness that once lay
 quiet at the bottom of the ocean,  and  over which
 shell-fish crept, that are now entombed within their
 layers..  Such convulsions were indeed often slow,
 and mayhave have occupied ages  in their progress
 of completion, for  the rocka that  were  diaturbed
 are frequently little confoaed, lying  around the
 central granitic  mass as a graceful robe; but go
 with me to the Alps, or even to our own English
 Cumberland, or  North Wales, and  I  could show
 you masses above masses which, when they were
 formed, lay as flat and even as the surface of  that
 floor, not only turned from their repose and tilted
 upward in the air, but, by the violence of the action
 that disturbed them, rolled over each other in  con-
 fused heaps, presenting  for miles  together to the
 puzzled explorer the aspect of a crumpled  and
 crushed sheet of paper.  Yes! there, indeed, has
 been power, immeasurable,  scarce even conceiva-
 ble ; but the giant Earthquake haa an arm capable
 of all thia work.   (Great applause.)
   I would now, ladiea and gentlemen, for one mo-
 ment digress from our course  and inquire,  if the
 force that formed Tycho was so great,  what be-
 came of the rocks that it  blew out of Tycho?  A
 cavern of that kind,  fifty-five miles in diameter, is
 not an infinitessimal thing which may  be  easily
 formed.  What became of theae rocka ?   Themost
 ready answer is  that they returned again to the
 surface of tbe Moon, just aa matter thrown from the
 Craters of our  Volcanoes returns  again to  the
 Earth. There are circumstances, however, I think,
 that will induce us to pause before we  assert  that
this took place.
  In the first place, tbe Moon being  a  small body
does not exert much attractive power over a mass,
therefore it would not take much  force to drive
away a body from the Moon altogether, and send it 
36
Prof. Nichol's Lectures.
flying about through space.  If this matter did  go
back, where is it?—we certainly should see it if it
was there.  Therefore we may say it is probable
that this matter did not go back to the Moon at all,
but that the violence of the shock was sufficient to
send it off to seek its own fortune  through space.
(Laughter and applause.)  Then what became of
it?   It must be moving through space in strange
orbits, in bodies of different magnitudes.  The orbits
of the planets areso regular that with them there is
no chance for collision, but with these masaea flying
round through apace there ia no chance  to escape
collision, consequently it is  to be expected  that
these masaea would be continually coming in  con-
tact with the Earth.  Thus may we account for
the falling of Meteoric stones.   This is not a strange
phenomenon.  At least two masses  must fall  to
the Earth per day—taking into account  all  that
have been observed to fall—a phenomenon  suffi-
ciently large to require some  important cause.—
Now, if tbis force had sent off this matter from the
Moon,  the Meteoric stones would  not be difficult
to explain.
  There was a theory concerning this phenome-
non called  the " Chemical Theory," which, as far
as  I  ever understood it, was thia.   " Sappooe
certain particles floating about in the atmosphere,
then suppoae particular forcea should cause theae
particles to come in contact and unite, then parti-
cular stones would be the result."  Now there are
three difficulties attending this solution.   First, it
cannot be established  "that  such particles were
floating about in the atmosphere."  Secondly—It
cannot be  proved that " particular forces would
cause them to unite;'' and  thirdly,  it cannot be
shown that " particular stones would result  from
their unition."  (Laughter and applause.) ,
  But  let me  return to our  direct subject.  We
have now collected sufficient indications to entitle
us to adventure some generalization  regarding the
seat of tbe force whose results we have  been ex-
amining ; but it may be well in tbe  first instance
to cast a rapid glance at other cratera than Tycho.
And I would aa another instance of this description
of formation claim your attention for one moment to
the crater Copernicus. This is one of the most beau-
tiful craters on tbe Moon's surface.  It is best seen
at tbe full of the Moon.  It seems aa if studded with
pearls—a most beautiful object lying in the midst
of a beautiful pearly light.  When this  light ia
analyzed we find tbat it, too, consists of a multi-
tude of bands shining like thoae around Tycbo;
but, unlike those firat bands, they wind along
through the valleys  of the undulating countriea,
and seem  more  like  our superficial streams of
lava.   This,  however, is the most remarkable
circumstance about  Copernicus.   Notwithstand-
ing tbe  violent effort necessary to  produce it,
the plain in its immediate neighborhood has  been
scarcely at all disturbed.  This very memorable
feature we remarked as connected with  the iso-
lated peak, and it is eminently characteristic of
the whole class of minor craters.   From thia.  truth
of vaat importance may be immediately inferred,
viz: that the seat of the convulsion cauaing these
craters cannot have been located deeply within the
Moon's mass.  A profound force, capable of pro-
ducing such a crater, must, at the same time,  have
shattered a considerable portion of the Moon's sur-
face.  No theory, then, at all related to tbe prevail-
ing conceptions of a central, force can be applicable
here.  The aapecta of the Moon are in this respect
wholly contradictory of the idea of a central force j
nay, a Geology formed upon the ground of the  ap-
pearances in  the  Moon  would not  contain  any
notion  of a central force.  It seems to me, then, not
unlikely that  that department of existing Geolo-
 gical theory which is founded  on the supposed
 action of central  forces, or on  supposed  relation-
 ships between the crust of the  planets and  their
 ao called molten interiors, will ultimately  undergo
 great modification.
  Another fact of great  moment seems to be ren-
 dered  probable by the  Moon, namely, that in the
 course of time  the upheaving energy has  been be-
 coming less convulsive, or that an epoch of compar-
 ative stability has  been approaching that body.
 [The Lecturer  showed, here, by aid  of diagrams,
 how the  relative  ages of the different  craters
 might be approximately ascertained. It seems that
 Tvcho is the oldest formation, and that aa the ages
 proceed, the craters appear to have  originated in
 leas and less violent actions.  This great fact also
 seems  establiahed in the Earth.]   He then con-
 tinued :
  Connected with this curious subject  there  is
 a more general  contemplation, on which notice
 ahould in conclusion be bestowed.  What is termed
 the argument or  consideration  of Final  Causes;
 that is an attempt to view any portion  of the known
 Creation as an indication of the original purpose of
 the Divinity has ever seemed to  me one which the
 human faculties cannot now undertake; for I can-
 not persuade myself that all  the fitnesses that we
 aee, multiplex aa they are, go to constitute the en-
 tire of that scheme which the Almighty, from  the
 innate  necessities of his own  perfections, deter-
 mined from the  beginning.  It is  thus, aa I think,
 that every  scheme observed  by man  has within it
 much of mystery, or, what is the same thing, points
 not  accounted  for, just because  theae touch on re-
 moter  forma of  being  and  mightier plans.  But
 though it isdenied us tospeak dogmatically in regard
 of anything tbat  we can see of the ultimate or pri-
 mary purposes of God; in no part of creation, great
 or small, when understood aright  is want  of har-
 mony descried, or that  adaptation which tells  of
 the exquisitenesa of the work of an Omniscient and
 Omnipotent Creator.  In reference to the scenes
 over which tonight we have traveled, we have
 found the long existence  of  eras  of unsettlement
 and commotion, and a  promiae of a period of re-
 pose.  Sympathizing with inorganic Nature, and
 toiling alone; with her, the vital  energies have a«-
 cordingly all along accommodated  their products to
 these  vast tranaitions.    Paasing  by the primal
 ages, it seems  clear that only when Nature's ac-
 tions became bo ordered that in the main they could
 foresee by ordinary prudence, was  the  Earth a
 fitting habitation for a being gifted with pure rea-
 son and will, and thereby cut loose from the safe-
 guard  of pure instinct.
  1 think the audience will understand this idea.—
 We can imagine creatures of instiuct fitted to live
 in any state in the world. We know that the in-
 stincts of animals forewarn them of dangers which
 man with all his boasted reason  cannot foresee.
 These beings of instinct can in many  cases foresee
 some of the greatcalamitiesof Nature.such as earth-
 quakes, volcanic eruptiona, etc.  The  beings of rea-
 son could not understand the approach of these dan-
 gers.  A world may be  adapted to the abode of be-
 ings under the control of instinct which would not be
 at all  adapted to the abode  of thoae compelled to
 trust for safety to their reason  alone. We know
 thatthere are some portions of the  Earth unfitted at
 the present, time for the habitation of Man—regions
 where the erections of civilization for years are over-
 thrown in  an hour; consequently,  in those portions
 of the Earth the inhabitants are, for the moat part,
 semi-barbarous.  This may  account  for the com-
 paratively  recent appearance of Man in the world.
! Long  before his appearance,  we find the Globe
| teeming with races of beings, but all of thorn of an 
Astronomy.
37
inferior creation to Man—beings of instinct.  Pass-
ing, then, I say, by the primal ages, it seems clear
that only when Nature's actions became so ordered
that in the main they could foresee  by ordinary
prudence, was the Earth a fitting habitation for a
being gifted with pure reason and will, and there-
by cut loose from the safeguards  of pure instinct.
Man then appeared : made his epoch.  The destruc-
tive forces still  prevailed, but not farther than, as
a whole, he could combat with ;  and he has fought
with them  and the sterile Earth, and achieved a
creation of his own.  The fitness of such a  being
for such a state is manifested by his triumphs;  for
while the earthquake has diminished  its subterra-
nean thunder, the marsh has  ceased to exhale its
poison, and culture has driven back the terrors  of
the once  eternal snows.  And  science shall pro-
ceed in unison with the change of great Nature.
until an epoch shall be  achieved when, external
foes all vanquished, our race shall see the Universe
everywhere as a friend and nowhere as  a foe;
when that repose shall be found fitted  for contem-
plation, flourishing  moatly in repose—contempla-
tions which are the object of  the yet least  devel-
oped faculties of our Human Nature—those  which
point to  the august pleasure of Immortality and
God.  (Great applause.) 
38
Prof. NichoVs Lectures.
                                     LECTURE  VII.

Cc/Mtitotfon of the SUN... .Discovery of apota on his surface and the rotation of the orb... .Nature of these apots....
   The solar atmosphere....Inquiry and  speculation concerning the cause of the  spots....Striking aimilitade with
   terrestrial atmospheric commotions or storms.... Probable existence of other changes in  the Sun.... Conclusion of
   the Course.
  Ladies and Gentlemen:  On the last evening,
 I opened to you in the cursory manner which alone
 is in accordance with a course so brief as  this, tbe
 question of the peculiar constitution of the several
  ?lanets which, with the Earth, roll round the Sun.
  n the course of that lecture we looked  especially
 at the Moon, and I think we saw cause  to modify,
 somewhat, the conclusion usually drawn by geolo-
 gists from the several modes of its development in
 Earth, respecting the ultimate character  of those
 grand causes  that have so universally upheaved
 the surface of all these planets.  The  conclusion
 we would be disposed to draw from  first sight  is,
'thatthis cause is a  central one; but I think we
 showed that this could not be the case.
  Those changes, however, to which I  then allu-
 ded,  are merely  a few scenes in the history
 of  the  planeta.   Now,  what  are theae  in re-
 lation to our  whole Syatem?   Incidents  them-
 selves in the  condensation  of the   Sun, just as
 their internal geological  epochs   are  incidents
 in  the course of their  own,  how utterly they
 shrivel and vanish from sight, when we turn to that
 Orb himself whose history.in very truth,the history
 of our System  solely is.   I  think 1 stated, on a
 previous evening, the fact  that tbe diameter of the
 Sun is so enormous when compared with the other
 bodies in our  system, that if  the Sun  be repre-
 sented by a globe two  feet in diameter, Jupiter
 would be represented by a ball  no larger than an
orange, and our own E artb by  a speck only.
  The phenomena that first led to some knowledge
 of the constitution of this vaat Orb,  are  those curi-
 ous spots that appear and disappear  so  frequently
 on his surface, and  which by their regular pro
 gression acroaa his diac, revealed to  their first dis-
 coverer, Galileo, the remarkable fact that the Sun
 rotates on his axis like the planets, carrying the
 spots along with him.
  We find, on examining the  Sun  with a good
Telescope, that rarely a day occurs in  which his
 surface is not  marked  by dark spots  which fre-
 quently appear with great suddenness, and disap-
 pear with exceeding rapidity.  This was one of
 the earliest discoveries of  Galileo.  On  looking at
tthem, he found they were  not fixed upon the Sun's
 surface,  but   were continually changing  their
 places.   Now,  on  endeavoring to ascertain what
 the cause of this change waa, he discovered that
 all the spots moved in one direction, and also in
 definite curves.  He found that all  these pheno-
 mena might be explained  by tbe supposition that
 the Sun is an immense globe turning on  its axis.
 He detected from thia,  alao, something like an ap-
 proximation to the time required by the  Sun to
 perform one revolution on its axis.   He estimated
 the period to be about twenty-five days.
  Before another step  was taken in this inquiry,
 very many years elapsed; nor was the  light they
 cast on the nature of the substance and constitution
 of tbe Sun recognized until tbe times of Dr. Alex-
 ander Wilson and Sir William Herschel,—the for-
 mer of these eminent men, earliest beyond a doubt,
establishing the cardinal  act in this high Inquiry
8ome remarkable features that invariably charac-
terize a Solar spot, had attracted his attention and
accident as he modestly said—but of course one of
those accidents  that can be taken  advantage of by
Genius, enabled him  through  them  to read the
whole  significance  of the phenomena.  The fea-
tures in question are these.
  The spots that attracted Dr. Wilson's attention—
a man whom I am proud to name as my almost im-
mediate  predecessor—were as follows :  In 1769,
a large  spot broke  out in the middle of the Sun
which  attracted the attention of all the  Astrono-
mers of that time.   He noticed that this spot was
moving onward,  and that  as  it passed  across
the surface of the Sun, a very singular  series  of
changes occurrred.   When in the Sun'a center, tha
spot presented the following phenomena, just as in
the fact do all the spots on the Sun's surface : He
found that  the  center was tbe only portion of the
spot tbat was quite  dark.  Around tbe center he
found an edging, which he called the Umbra.  As
the spot went forward, the Umbra diminished; and
when it went on still farther the  Umbra  disap-
peared, and nothing but the edging on the side op-
posite him8elf waa  visible.  [Here the Lecturer
referred to  a couple of large diagrams, represent-
ing the various phenomena presented by   these
Solar spots.]
  In explanation of  these  phenomena,  Wilson
formed a very ingenious theory.  He said, if this
large spot lasts  long enough for the Sun to bring it
round again, I shall see the following phenomena:
As it comes round,  1 shall see, first, the opposite
edging,  and as it comes  on  down to the center of
the Sun, I shall see the spot with  its black center
surrounded  with the edgings.  Well, the spot did
continue long enough for Wilson  to make the de-
sired observations, and he found his predictions in
every respect verified.  [The Lecturer here ex-
hibited, by  means of a common globe, the course of
reasoning pursued  by Wilson in the formation of
his  theory.]
  It followed at once, from Wilson's  capital dis-
covery, that our magnificent Luminary is not a cha-
otic conflagration, but a body having a definite or-
ganization, revealed in so  far by the aspects of
these openings; and to the solution of the momen-
tous question as to what this organization  is, the
singular powers of the elder Herschel came quickly
in aid of the efforts of his friend.  With both of
these illustrious men, it early became a  fixed be-
lief  that the surface thus broken by chasms must
be aerial—or some  elastic gaseous fluid like our
atmosphere; for notwithstanding  the magnitude
of these spots, sometimes reaching  even   50,000
miles in diameter—they open and close with a
rapidity next to  marvelous, often surpassing the
rate of 1,000 miles  a day.
  Nowhere, perhaps,  in all the annals of  disco-
very, is there  aught that more stirs thought or
raises more strange questions than this !  Let  ua
see into what it summons us to inquire. 
Astronomy.
39
  I. The play of sudden, tremendous and evanescent
 forces, either connected with the solid body of the
 Sun or generated within bis atmosphere,  has be-
 come an absolute fact;  now  where and what are
 these 7  But in the firat place, and passing beyond
 the apota, let ua briefly review the whole known
 phenomena.
  There appears no rest whatever In  the atmos-
 {ihere of the Sun.  Over all its  surface, waves of
 ight seem to dart incessantly, asauming the moat
 varied aapects.  Tbe bright part, aa Herachel early
 discerned,  is  full of inequalities,  showing first,
 parts more brilliant than the rest, sometimes round,
 sometimes elongated—mountain  billows in  that
 light ocean. Then there  are large dim spots ex-
 tending over immense tracts, but showing no dark
 center—constituting what Herschel termed shal-
 lows.
  We find that these spots are  not fixed, but are
 continually dashing along the center of the  Sun.
 Now, when we come to the consideration of the
 spots themselves, we  find them characterized by
 certain  remarkable phenomena,  wbich will enable
 us to ascertain their cause.  A spot never appears
 twice in the same place; but although  they are
 not confined to a point,  they are confined to regions.
 They always appears in the Sun's torrid zone.  We
 never find the  spot breaking out beyond that belt.
 Then, again, on looking more minutely, we find the
 spots  themselves have  amotion—a motion besides
 that which tbe rotation  of tbe Sun causes, and it is
 moat peculiar.   We find that the spots which ap-
 pear North of the Sun's  Equator, move slowly
 toward  the North, till  they get to the temperate
 regions, and then disappear.   No  instance baa
 been known of spots formed in the North going
 South.  Just so, spots  of the South move toward
 the South temperate zone and disappear.
  There is still another circumstance characterizing
 the mode  in which  they disappear.   Sometimes
 they go on till  they get  to the Sun's temperate re-
 gions and then quietly die away.  At other times,
 they do not disappear in this manner, but split up
 just as  if  they  were  exploded by some violent
 force.   This phenomenon I had the good fortune
 once to  witness.  It is  most remarkable.  It has
 been compared to this:   Suppose  a person stand-
 ing upon a frozen pond  should take up a piece  of
 ice and  cast it from  him.  Now, this mass of ice
 would be broken into a  vast number of fragments,
 which would be  scattered over the surface of the
 pond.  This is  exactly the manner in which these
 spots appear to be dashed  and scattered over the
 surface of the Sun.
  I have now unfolded all the phenomena exhibited
 by the Solar spots,  and we must now direct our
 endeavors  to  ascertain their explanation.   (Ap-
plause.)
  If, uuappalled by the  majesty of the orb on which
 they proceed, or  by  the magnitude of the forces
 causing them, we propose  to ourselves under the
 consciousness of the all-prevalence of Law, to seek
 out something analogous in  our own  planet, we
 will find them  nowhere save among the phenome-
na of the winds.   But the analogy is every where,
 moat atrihing, and probably the moat complex and
 imposing aapects of the  surface of the Sun.  In ref-
 erence to the bright parts which we deem heapings
 up of the shining atmosphere, as well as to the
 shallows which with the brighter parts are spread
over it. our attention is inevitably drawn to the
 great  Barometic changes  that take place on the
surface of our globe.  You are aware what a change
in the Barometer re ally means. It is this i The Bar-
ometer tells you  whether the column of air above
you ia growing lighter or not.  If lighter, the  Bar-
ometer rises—if heavier, it falls.  Now, until com-
paratively lately, the theory with respect to the
change of weight in  the  column of air above us,
was this : It was attributed to cbangea in the inte-
rior of tbat column.  It was supposed that the air
composing itunderwent alterations in temperature.
But another theory has been propounded, viz. that
the changes in the weight of the column are caused
by alterations in its bight, tbe column not remain-
ing at the same elevation, but that it is continually
changing—undergoing vast undulations, rolling like
mighty billows.   Now, you will observe that if we
were outside of the earth and the upper portion of
our atmosphere were, like the Sun's, self-luminous,
then these waves would cause by their  various
commotions, appearances similar to the spots seen
on the  surface of the Sun.  If we are  right, then,
the significance of these remarkable phenomena is
clear.   They indicate the surging of the Solar aerial
masses.  They are in fact the visible markings of
the Solar Barometers;  and through these, one day,
may come to Science a knowledge of how the winds
roll there, and what are their grand periods.
  This inquiry is the most difficult tbat the astron-
omer has to pursue.  We cannot look at the Sun
with the naked eye; and the telescope augments
bis light. On this account we are compelled, when
viewing the Sun, to  use dark glasses, which de-
tracts very much from the accuracy of our observa-
tions.   I confess that it has sometimes occurred to
me, that we ought, before this,  to have got at a
means which would enable us to observe the Sun
with much greater accuracy than we have hereto-
fore been able to do.  I refer to the Daguerreotype.
You all understand what  has  been accomplished
by this.  Now, if by the aid of tbe  Sun, we can
produce the most exact likenesses of whatever ob-
ject we choose, I do not see why we should not re-
quest the Sun to write down his own image.  (Ap-
plause.)  For myself, I cannot see  the possibility
of failure. It is quite  common  to mount the teles-
cope upon machinery, so as to enable it to follow
the movements of the heavens throughout the day.
Now, if we could fit up the telescope with  these
Daguerrean plates and point it at the Sun, we could
in one day get a sufficient number of images, that
we might take to our closets  and examine with
our microscopea, to enable us  to  completely unfold
the constitution of the Sun.  (Applause.)
  Let me ascend, however,  to what is far more
striking.  I will here remark that I am sure I need
not explain to my audience  what a boon it was
when the hurricanes of the Tropical Regions yield-
ed up the secret of their cause.   I believe the gen-
tleman to whom tbe world is indebted for this dis-
coverv is a resident of this City. His  name is —
[we did not catch the name].   I see him in the au-
dience.   (Applause.)   These hurricanes are whirl-
winds.  They do not owe their power to the velo-
city with which they are moving over the earth,
but to the velocity of their rotation.  These hurri-
canes, then, are revolving cylinders of air, hollow
in the center. Suppose, now, one were outside the
atmosphere of the earth and looking at one of these
phenomena.  How would it appear 7  A mere spot,
exactly resembling those we observe upon the
Sun.  Generally,  these cylinders  are  round.  In
passing over a  regular country, they would be
round and regular;  but if passing over  a rough
country, bills and mountains, they would be round
but somewhat irregular.  Now  tbe  spots  on the
Sun are not exactly round. Therefore, if they are
analogous to those of the earth, they show  the as-
pect of the ground over which  they pass.  Now,
observe tbe  regions in which these hurricanes ap-
pear: always in the Tropical Seas.  Those occur-
ring north of the Equator, move toward the north;
while that occurring south of the Equator  always 
40                              Prof. Niclu

move toward the South.  Just so'with those in the

  The thought is, indeed, overwhelming, when
from these hurricanes, ay, or from the devastating
Typhoon, we pass to  tornadoes apparently similar
in the atmosphere of  the Sun, by whose inconceiv-
able motion an opening of 50,000  miles in diame-
ter may be made, extending through  the entire
depth of that atmosphere, probably many thousand
miles.  And  yet, is  not the electric spark with
which the child disports itself, a key to tbe rending
of tropic thunder?  Is not the power of life which
Bustains the smallest wild flower exactly that which
infuses strength into the giant pine  and causes it
to evolve its  mighty  branches ?   Yes!  To these
stupendous laws which, as ministers of God, work
at the deep root of things and cast up all these
wondrous phantasmB, no event is  small, no acci-
dent unthought for; we dwell in a Universe where
not a floweret fades unseen, where the very hairs
of our heads are numbered!  (Great applause.)
  My audience will  observe, however, that in so
far as we have gone, we have not established any-
thing to entitle us to  say that these phenomena
upon the Sun are the same as those I have repre-
sented upon the earth.  We have observed strong
analogies indeed, but we must show that the causes
whieh produced these phenomena upon the earth
may  operate upon the  Sun.  Now, you will  ob-
serve, in the first place, that I have drawn all these
phenomena from the  winds.  Now can winds ex-
ist upon the Sun.  What is the cause of winds?  It
is simply this:  The atmosphere in different por-
tions of our globe is unequally heated.  If all parts
were heated in the same degree, there would be no
winds.  One cause of the difference in heat on the
Earth is the shining of the Sun.  At the Torrid
Zone, his rays are vertical, or  nearly so, which
renders his heat intense, while at the North and
South his rays are very oblique;  consequently  the
degree of heat in those regions is much less than it
is in the Torrid Zone.  Now.it is  impossible that
this cause should operate to produce winds in  the
Sun. There is another important cause, however,
of winds in the Earth which may exist in the Sun,
viz: a difference in materials.  This difference is
such that if the rays of the Sun should come down
exactly the same on all parts of the Earth, the dif-
ference in the degrees of heat would be very great.
Take, for instance, a case of the Sun  shining on
the sand and on the water.  The sand on the mar-
gin of a river may be scorching hot, while the wa-
ter is very cool.  Now, where are the hot regions
on the Sun,  and where are  the cold?  Where is
the Continent 7  Where is the Ocean ? Now, this
inference is within the range of Science. There is,
however, a difficulty in carrying the explanation
out.  It is very probable that the phenomena of
these hurricanes of  ours are owing to the trade-
winds.  Now we cannot determine trade-winds in
the body of the Sun.   The question with respect to
these lies open for farther observation.
   Here, then, is  another  field of most engrossing
speculation.  This, even, that these surgings in the
Solar atmosphere are the key by which future gen-
erations may unlock his character, shrouded though
now he is in his noble and impenetrable splendor!
This  is the  wing on which Intellect  may pass
where vision never can, and explore the hidden
Orb, examine his continents and oceans, his plains
and  majestic mountains.  And why  incredible?
Why should  not Intellect pass, as of yore, where
the feeble eye can never reach 7  For note the his-
tory of this very discovery!  Once an acorn, al-
ready it has become a young oak with many
branches,  and nought shall hinder it to stretch yet
farther toward the skies! When Galileo through
Vs  Lectures.

 his rude Telescope first noted a few dark specks on
 the disc of the burning Sun, that globe of fire, as
 people thought, men were all struck in amaze, ass
 because of their amaze almost would have atoned
 him.  Time rolled by, during which some  thought
 that the spots were the ashes of the  burned Sun;
 others that they were the dark souls of the pun-
 ished floating in fire.  (Laughter.)  A great man
 then analyzed the spots and determined their char-
 acter. By degrees, and  only  by degrees, and by
 the efforts of separate thinkers, they have  come to
 be considered as a class, and those laws sought to
 be discerned on which deeper questions certainly
 depend.  Tell me not that Thought shall stop or the
 Human Intellect here be stayed. The mighty Ava-
 lanche grows among its native hights unseen by
 Man, silent and unknown for ages; but as its mass en-
 larges, though  it  be  but by the fall of flake  after
 flake of the downy snow, the moment of its free-
 dom is surely approaching—the moment when, de-
 livered from bondage  by a stroke of sunlight, it
 shall thunder to the plain, and the mountains shall
 shake with the echoes of its powers!  (Great ap-
 plause.)
  II.. Another subject  remains still more stirring.
 If our views of the Sun  are correct, he is distin-
 guished from the planets that encircle him  only by
 his phosphorescent robe.   Now what  is tbat phos-
 phorescence?  Is it peculiar, is it permanent?
  Again  we descend to our own planet, and our first
 thought leads us to the Auroras.  Whatever  their
 origin, they, show the existence of causes in virtue
 of whose energy the upper strata of our atmosphere
 become self-luminous sometimes in a high degree,
 for in Northern regions our travelers have read by
 their brilliance. But the  Aurora is  not the  only
 phenomenon which indicates the  existence of a
 power in the matter of our globe to emit light.
  You have all heard of these  brilliant  Auroral
 phenomena.  It is supposed,  that in a previous
 epoch of our globe, these phenomena  were mani-
 fested in a much higher degree than now.  On the
 Melville Islands we find plants which  I should call
 ultra-tropical.  They are much too large to grow
 on the Earth now. These plants must have  enjoyed
 an immense amount of heat and light.  Whence
 could they derive these ?  They could not be de-
 rived from the  Sun, while  the axis of our Earth re-
 mains at  the  same inclination as now:  and, of
 course, we have  no reason  to believe that it has
 ever been  situated otherwise  than at present-
 Consequently, we muat infer that our Earth did
 possess,  at some former epoch, the power of emit-
 ting a sufficient amount of heat and light to sustain
 the growth of these plants.  The existence of this
 illuminating power, although apparently in its de-
 bilitude;  we discern also in appearances among the
 other orbs.  Flashes like our  Aurora are said to
 have been observed over  the dark hemisphere of
 Venus and the obscure part of the Moon is believed
 to have  been  visited by similar phenomena; but
 the circumstance most remarkably corroborative of
 the  mysterious truth  to  which these indications
 point is the appearance of our midnight Luminary
 during a total eclipse.
   When the Moon  is  totally  eclipsed, you are
 aware that it goes entirely into the Earth's shadow.
 No light comes to it, therefore, from the Sun. There
 may be some stray rays;  but calculation shows us
 that they  are not sufficient to cause any apparent
 diminution of the eclipse.  Well, then, in what po-
 sition ought the Moon to be, when totally eclipsed 7
 She should disappear  entirely, should be blotted
 out from the sky.  But on the. contrary, instead of
 being blotted  out, she is perfectly visible in  the
 sky, an immense bronze disc, and with the aid of a
 telescope, all her phases can be traced. Now, this 
Astronomy
41
 could not be, unless the Moon were sending out
 light herself.
   From all these circumstances, there seems no
 tenable conclusion save this; that the matter  both
 of Sun and planets is  capable in  certain circum-
 stances, whose exact conditions are not known, of
 evolving the energy we term Light;  and that the
 atmosphere of the  Sun is  at present under influ-
 ences favorable  to the high manifestations  of a
 power which from  the other orbs  has not  wholly
 departed.  And thus forever  is broken down  that
 supposed distinction, which seemed to place our
 central luminary apart in  space to an immeasura-
 ble extent from the humble worlds that roll around
 him.
   It will naturally be expected, that if our theory
 be true, if the power to evolve light be  subject to
 change, it may have left its impress on that farthest
 field of its energy—the wilderness of the Fixed
 Stars.   Now, startling though it at first sight must
 appear, on  all sides,  there are  here marks of
 change  and  of the modifications  of light-giving
 power.   The  Stars have changed their  colors.
 They have been described  by their colors. Poets
 used to call Sirius the " Red Dog-Star:"  Now it is
 the whitest star in  the Heavens.  The stars have
 also altered their quantities—they have diminished
 their  magnitude  without  changing their  place.
 Tycho, a Danish astronomer saw one night in the
 constellation  Cassiopea,  a  most  brilliant  star
 which he had not previously noticed.  He watched
 it for a year.  It grew brighter and brighter until
 it became as light as Venus.  After a  year, it be-
 gan to wane,  and continued waning and waning,.
 exhibiting the appearance of a dying conflagration.
 This is but a rapid instance of that change which
 is constantly going on among the stars.
   Sir John Herschel, at the Cape of Good  Hope,
 witnessed a similar phenomenon.   He  saw, on
looking at the Star n Argus, it was brighter than
 laid down in the catalogues.  It was  originally a
 star between the second and third magnitudes.  It
 went on increasing till it became not only a  star
 of the first magnitude, but the third star in bright-
 ness  ia the whole skies, after which it began to
 wane.   Herschel's theory was,  that there are
 what might be called cosmical clouds floating about
 in space—that these clouds intervene between us
 and  the stars, thus darkening them.  Thia theory,
 however, is not  generally  received.  Why,  it is
 asked, do not these clouds dim other stars 7  Espe-
cially, with reapect to this Star of Tycho, how
^could a cloud have rested before it, from the be-
ginning of time, and just went away for a year and
then returned again 7  I think we are bound to re-
ject this explanation.
  Deeper, far  deeper among Nature's potencies
must be the origin of theae astonishing displays.—
Doubtless they result from varied comminglings of
the energies that produce light, and which, as we
have seen, act  far and near. And here as Time rolls
on, these, like others, are ever weaving a devious
web, their product, Light, must, as ages course,
sparkle variously in every portion of their vast do-
main.   And thus one other fanciful tradition disap-
pears !  No more is Light inherent in the Sun than
in Tycho's vanished Star ; and as with it and other
orbs, a time may come when through the concert of
all the powers of Nature, he may cease to be  re-
quired to shine.  And if even now he is only in one
stage of this majestic mutation—if, as the Planets
have rolled on and worked out their fates under his
beams, he, the Vivifier, has been changing and yet
must farther change—once more are we  in pres-
ence of revolutions that seem illimitable—of pro-
gressions whose vista reaches to the very infinite—
and we are but as points amid accumulating, super-
imposed immensities—flashes  from  the wheel of
the Burning Car—creatures we know not what!
  Oh what a world is this!  Change rising above
change, cycle growing out of cycle in majestic pro-
gression, each  new one  ever widening—like the
circles that wreathe from a spark of flame,  elon-
gating as they  ascend, finally to become lost in the
empyrean!  And if all that we see—if from Earth
to Sun and  from Sun to the Universal Star work—
that wherein we the  best behold images of Eter-
nity, Immortality and God—if that is only a  state or
phase of a course of Being rolling onward evermore
—what  must  be  the Creator, the Preserver, the
Guide of all.  He at  whose  bidding these phan-
tasms come from nothingness and again disappear,
whose Name—amid all things—alone is EXIST-
ENCE—I AM IN THAT 1 AM!   The  AU-En-
compasser: the All-Sustainer!   He  enwraps, He
upholds all those gorgeous  Heavens!  Yea, un-
assisted, uncounseled, sustains he not unchanged
and  unchangeably forevermore, even  the fabric
of His own Awful Being! Reverentially before him
—humbly grateful that in the course of this benefi-
cent arrangement He has permitted such intima-
tions of  his glory to reach  us—let us conclude in
tbe rapt language of the Psalmist: How manifold.
oh God,  are thy works, by wisdom Thou hast made
them all!
« 
                  POPULAR   LECTURES
                                       ON


 SCIENCE     AND     ART;
                               DELIVERED IN  THE
            CHIEF  CITIES AND TOWNS IN THE UNITED STATES,
                      BY DIONYSIUS LARDNER,
Doctor of Civil Law, Fellow of the Royal Societies of London and Edinburgh, Member of the Universities of
        Cambridge and Dublin, and formerly Professor of Natural Philosophy and Astronomy
                          in the University of London, &c. &c.
  After Dr. Lardner had  brought to a close his Public Lectures in the United States, he waa
prevailed upon by the Publishers to prepare a complete and authentic edition  for publication.—

The general interest which, for a period of several years, these beautiful expositions and commen-
taries on the Natural Sciences had excited, and which was so universally felt and acknowledged,
induced the Publishers to believe that their publication would be most acceptable, as well as per-
manently beneficial, to the American public.  In these published Lectures  it will be found that

the Author has preserved the same simplicity of language, perspicuity of reasoning, and felicity of
illustration, which rendered the oral discourses ho universally popular.  While the Work was
passing through the press, and as the different Numbers or Parts were circulated, the Publishers
received from all sections of the Union the most flattering encomiums of the usefulness of the work
and of the manner in which it wa.s printed and illustrated.  It was gratifying to the Publishers to

notice the interest taken in the work by Mechanics.  In one workshop in  New-York, Thirty of
the Journeymen purchased the Numbers as they were published; and, in several large establish-
ments, the workmen formed clubs and purchased the work at the wholesale  or dozen price.  The
number of Lithographic  and Wood Engravings, large and small, in the whole series, is 3SO.

  We do not know that we can give a better idea of the work, to those who have not seen it, than
by publishing the following summary of the matters treated of in the different Lectures:

                                         1838-9—Various Auroras seen by him—Theory of
                                         Biot—Objections to it—Hypothesis of Faraday—Au-
                                         roras seen on the Polar Voyage of Captain Franklin,
                                         &.c. &c.

                                               LECTURE V.....ELECTRICITY.
                                          Electric Phenomena observed  by the Ancients—
                                         Thales—Gilbert de Magnete—Otto Guencke's Elec-
                                         tric Machine—Hawkesbee's Experiments—Stephen
                                         Grey's Discoveries—Wheeler and Grey's—Dutaye's
                                         Discovery—Invention of the  Leyden Vial—Singular
                                         Effects of the first Electric Shocks—Experiments of
                                         Watson and Bevis—Experiments on Conductors-
                                         Franklin's Experiments and  Letters—His Experi-
                                         ments on the Leyden  Vial—His Discovery of the
                                         Identity of Lightning and Electricity—Reception of
                                         his Suggestions by tlie Royal  Society—His Kite Ex-
                                         periment—His Right to this  Discovery denied by
                                         Arago—His Claim Vindicated—Invention of Conduct-
                                         ors—Canton's Experiments—Discovery of Induction
                                         —Inventor of the Condenser—Works of /Epinua—
                                         1 heory of Symmer—Experiments of Coulomb—Bal-
                                         ance of lorsion-Electricity  of the Atmosphere-
                                         Effects of Flame—Experiments of Volta—Lavoisier
                                         and Laplace—Analytical Work of Poisson.

                                          LECTURE  VI.....THE MINOR PLANETS.
                                          itary-Transit over the Sun-Relative Positio.
                                         -Difficulty of Ooserving it-Pewits—Diurnal Motion
                                         of Venus and Mercury indioated  by the Shadows of
                                         Mountatns-Axjs of Rotation-Seasons, Climates,
                                         and Zones—Orbits and 'IVansits of Mercurv and Ve-
                                         nus-Mountams  on Mercury and  Venus—Influence
                                         of the Sun at Mercury and Venus-Twilight on Mer-
                                         cury and Venus-AJars-Atmosphere of Mais-Phya-
                                         ical Consmution of  Mars-Has Mars a Satellite i—
                                         Appearance of the Sun at Mars, &c.
 LECTURE I__THE PLURALITY OF WORLDS.
   Contemp>.rion  of  the Firmament—Reflections
 thereby suggested—Limited lowers of the Tele-
 scope—'What it can do for us—.'is effect on the Ap-
 pearances of the Planets- Are the Planets inhabit-
 ed ?—Plan of the Solar System—Uniform Supply of
 Light and Warmth—Expedient for Securing it—
 Different Distances of the Planets do not necessarily
 infer different Temperatures, nor different  Degrees
 of Light—Admirable Adaptation of the Rotation of
 the Earth to the Organization of its Inhabitants—Mi-
 nor and Major Planets—Short Days on the latter—
•The Seasons—Similar Arrangement on the Planeta—
 The  Atmosphere—Many Uses of the Atmosphere—
 Clouds—Rain, Hail, and  Snow—Mountains on the
 Planets—Land and Water—Weights of Bodies  on
 the Planets—Appearances of the Sun, &c. &c.

        LECTURE II.....the sun.
  The Most Interesting Object in the Firmament—
 Its Distance—How Measured—Its Magnitude—How
 Ascertained—Its Bulk  and Weight—Form—Time of
 Rotation—Spots—Its Physical Constitution—Lumin-
 ous Coating—Temperature—Luminous Matter, &c.
 &c.
       LECTURE III.....eclipses.
  Lunar and Solar Eclipses—Causes—Shadow of the
 Earth—And Moon—Magnitude—When they can hap-
 pen—Great Solar Eclipse described by Halley—Eclip-
 tic Limits, &c. &c.

 LECTURE IV.....THE AURORA BOREALIS.
  Origin  of the Name—Produced by Electricity—
 General Phenomena of Auroras—Various Examples
 of this Meteor—Biot's Excursion to the Shetland
 Isles to observe the Aurora—Lottin's Observations in 
DR.  LARDNER S LECTURES.
  LECTURE VII.....WEATHER ALMANACS.
  Merits of Weather Almanacs—Fright Produced by
 Biela's Comet—London Water Panic—London Air
 Panic—London Bread Tame—Rage for Weather Al-
 manacs—Patrick  Murphy's  Pretensions—Compari-
 son of the Predictions with the Event—Morrison's
 Weather Almanac—Charlatanism of these Publica-
 tions—Great Frost of 1638 in London—Other Visita-
 tions of Cold.

    LECTURE  VIII.....HALLEY'S COMET.
  Predictions  of  Science—Structure  of the  Solar
 System—Motion of Comets—Intervals of their Ap-
 pearance—Halley's  Comet—Its  History—Newton's
 Conjectures—Sagacity  of  Voltaire—Halley's  Re-
 searches—Foretells  the Appearance of the Comet—
 Principle of Gravitation applied to its Motion—Anec-
 dotes of Lalande and Madame Lepaute—Minute and
 Circumstantial Prediction   of the  Reappearance of
 Halley's Comet—Discovery of  the Planet Herschel
 anticipated  by Clairault—Second  Prediction  of ita
 Return in 1835—Prediction fulfilled— Observations
 on its Appearance in 1835, &c. &c.

     LECTURE IX.....THE ATMOSPHERE.
  Atmospheric Air  is Material—Its Color—Cause of
 the Blue Sky—Cause of the Green Sea—Air has
 Weight—Experimental Proofs—Air has Inertia—Ex-
 amples of its Resistance—It  acquires Moving Force-
 Air is  Impenetrable—Experimental Proofs—Elastic
 and compressing Forces equal—Limited Hight of the
 Atmosphere, &c. &c.

    LECTURE  X.....the  new planets.
  Indications of a Gap in the Solar System—Bode's
 Analogy—Prediction founded upon it—Piazzi discov-
 ers Ceres—Dr. Olbers discovers Pallas—Harding dis-
 covers Juno—Dr. Olbers discovers  Vesta—Indica-
 tions afforded by these Bodies of the Truth of Bode's
 Predictions—Fragments  of  Broken Planet—Others
 probably still  Undiscovered—Singularities of their
 Appearance, <fcc. &c.

        LECTURE  XI.....the tide?.
  Correspondence between  the Tides and Phases of
 the Miv>on shown by  Kepler—Erroneous popular No-
 tion of the Moon's Influence—Actu»!  Manner in
 which the Moon Operates—Spring Tides—Counter-
 action of the Sun and Moon—Neap Tides—Priming
 and La\gging of the Tides—Effects of Continents and
 Island"! on the Tides—General Prosress of the Great
 Tidal Wave—Range of the  Tide, <fec. &.c.

         LECTURE XII.....light.
  Structure  of the  Eye—Manner in which Distant
 Objects become Visibly—Velocity of Light—Account
 of its Discovery by Roomer—Measurement of the
 Wavsn of Light  by Newton—Color produced by
 Wave* of different" Magnitudes—Corpuscular  The-
 ory— Undulatory Theory—Relations of Light and
 Heat, &c. &c.

 LECTURE XIII.....the  major planets.
  Space between Mars and  Jupiter—Jupiter's Dis-
 tance and Period—Magnitude and Weight—Velocity
 —Appearance of Disk—Day and Night on Jupiter-
Absence  of  Seasons—Telescopic  Appearance—His
Belts—His Satellites—The Variety  of hia  Months-
 Magnificent Appearance of the Moon as seen  from
Jupiter—Saturn—Diurnal Rotation—Atmosphere—
His  Rings—Their  Dimensions—Appearances  and
Disappearances of the Rings—Satellites—Herschel
or Uranus—Distance and Magnitude—Moons—Rea-
sons why there is no Planet  beyond his Orbit.

LECTURE XIV.....reflection of light.
  Ray of Light—Pencil of Light—Reflection—Its
Laws—Image of an Object in a plane Reflector—Re-
flection of Curved Surfaces—Concave Reflectors-
 Convex Reflectors—Images in spherical Reflectors—
Illusion of the air-drawn Dagger—Effects of common
Looking-Glasses Analyzed—A Fluttering  Glass ex-
plained—Metallic Specula—Reflection  in  Liquids-
Image of the Banks of a Lake or River.
LECTURE XV.......prospects of steam
                 navigation.
  Retrospect of Atlantic Steamers—Origin  of the
Great Western—Cunard Steamers—Can Steam Pack-
et-Ships be successful?—Defects of Common Pad-
dle-Wheels—Defects of the present Steam-Vessels
as applicable to War—Difficulty of long  Ocean-
Voyages—Ericsson's Propeller—Loper's Propeller—
Method of raising the Propeller out of the Water
—Fuel—Form  and Arrangement of the  proposed
Steam Packet-Ships—War  Steamers—The  Prinee-
ton, &c. &c.

   LECTURE XVI.....the  barometer.
  Maxim of the Ancients—Abhorrence of a Vacuum
—Suction—Galileo's  Investigations—Torricelli  dis-
covers tbe Atmospheric Pressure—The Barometer—
Pascal's Experiment—Requisites for a good  Barom-
eter—Means of securing  them—Uses of the Barom-
eter—Weather-Glass—Rules in common Use absurd
—Correct Rules—Measurement of Hights—Effect of
a Leather Sucker—How Flies adhere to Ceilings, and
Fishes to Rocks—Breathing—Common  Bellows—
Forge Bellows—Tea-Pot—Kettle—Ink  Bottles—
Pneumatic Trough—Gurgling Noise in  lecanting
Wine.

      LECTURE  XVII.....the moo*.
  Popular Interest attached  to the Moon—Ita Dis-
tance—Rotation—Same Face always toward  the
Earth—Phases—Changes of Position—Atmosphere—
Optical Test—Physical Qualities  of  Moonlight—Is
Moonlight Warm  or Cold 1—Does Water Exist  on
the Moon ?—Does  the Moon Influence the Weather!
—Mode of determining this—Physical Condition of
the Lunar Surface—Appearance of the Earth as 6een
from  the  Moon—Prevalence of Mountains upon it
—Their  general  Volcanic Character—Telescopic
Views of the Moon—Condition of a Lunar Crater,
&c. &c.

        LECTURE XVIII.....heat.
  Heat as a Branch of Elementary Physics neglect-
ed—Is a Universal Agent in Nature—In Art—In  Sci-
ence—Astronomy—Chemistry—In  every  Situation
of Life—Applications of it  in Clothing and artificial
Warming and Cooling—Lighting—Admits of easy
Explanation—Thermometer—Melting and  Boiling
Points—Evaporation—Specific Heat—Heat produced
by Compression—Radiation—Conduction—Incan-
descence. &.c.Sic.

LECTURE XIX......the  Atlantic  steam
                  question.
  The Project proposed in 1835—Previous Condition
of Steam Navigation—Practicability  of the Atlantic
Voyage not denied or doubted—Report of  the Meet-
ing of the British Association at Bristol—Extract from
the London  Time*—Ocean Voyages for  Steamers
and Sailing Vessels compared—Effect of the West-
erly Winds in the Atlantic—Cunard Line of Steam-
ers—The Support received by them from the British
Post-Office—Failure of the Project to Establish New-
York  and Liverpool  Steam-Liners—Essay  on  the
Question, " Has Atlantic Steam Navigation been Suc-
cessful*"  &.C &c.

       LECTURE XX.....galvanism.
  Origin  of  tbe Discovery—Accidental  Effect  on
Frogs—Ignorance of Galvani—His Experiments  on
the Frog—Accidental Discovery of the Effect of Met-
allic Contact—Animal Electricity—Galvani Opposed
by Volta—Volta's Theory of Contact Prevails- Fab-
roni's  Experiment—Invention of the Voltaic Pile—
Napoleon's Invitation' to Volta—Anecdote  of Napo-
leon—Decomposition of Water—Cruickihank's Ex-
periments—Davy commences his Researches—Calo-
rific Effects of the Pile—Davy's celebrated Bakerian
Lecture—Prize awarded him  by the French Acade-
my—His Discoveries—Decomposition of Potash and
Soda—New  Metals.  Potassium and  Sodium—Dis-
covery of Barium—Strontium, Calcium, and Magne-
sium—Rapid Diacovery  of the other  new Metals,
&.c. <fcc. 
DR.  LARDNER's LECTURES,
LECTURE  XXI.......the moon  and the
                 weather.
  Ancient  Prognostics  of Aristotle,  Theophrastus,
Aratus, Theon, Pliny, Virgil—Recent Predictions-
Theory of  Lunar Attraction not in accordance with
Popular Opinion—Changes of Weather compared
with Changes of the Moon—Prevalence of Rain com-
pared with Lunar Phases—Direction of the Wind-
Erroneous ■ Notions of Cycles of nineteen and nine
Years—Cycle of four and eight Years mentioned by
Pliny.

  LECTURE  XXII.....periodic comets.
  Eucke's  Comet—Its Period and Orbit—Motion-
Newton's Conjectures  respecting  Comets—Biela's
Comet—Its Period and  Orbit—Lexell's Comet-
Causes of its Appearance and Disappearance—Whis-
ton's Comet—His Theory—Did this Comet produce
the Deluge ?—Orbit of this Comet, &c. &c.

LECTURE  XXIII.....radiation of  heat.
  Radiation a Property of Heat—Prismatic Spectrum
—Invisible Rays—Two  Hypotheses—Invisible Rays
alike in Properties to Luminous Rays—Discoveries
of Leslie—Differential  Thermometer—Radiation,
Reflection, and Absorption—Effect of Screens—Sup-
posed Rays of  Cold—Common Phenomenon Ex-
plained—Theory of Dew, &c. &.c.

LECTURE  XXIV....meteoric stones and
              shooting stars.
  Appearances accompanying Meteorites—Theories
to explain  them—Shooting Stars—November and
August Meteors—Orbits and Distances—Hights.

     LECTURE  XXV.....the  eabth.
  A difficult Subject of Investigation—Form—How
proved  Globular—Magnitude—Annual  Motion—El-
liptic Form of its Orbit—Proofs of its annual Motion
from the Theory of Gravitation—From the Motion of
Light—The Earth's diurnal Motion—Inequalities of
Day and Night—Weight of the Earth—Experiments
—Density—The Seasons—Calorific Effect of the Sun's
Rays—Why the longest is not th» hottest Day—Why
the shortest Day is not the coldest—The hottest Sea-
son takes place when the Sun  is farthest from the
Earth—Diurnal Rotation—Form of the Earth.

 LECTURE  XXVI.....lunar  influences.
  The Red Moon—Supposed Effect of the Moon on
toe Movement of Sap in  Plants—Prejudice respect-
ing the time  for felling  Timber—Its Prevalence—
Prejudices respecting its Effects on Grain—On Wine
—On the Complexion—On Putrefaction—On Wounds
—On the Size of Oystors and Shell-Fish—On the Mar-
row of Animals—On the Weight of the Human Body
—On the, lime of Births—On the Hatching of Eggs—
On Human Maladies—On Insanity—On Fevers—On
Epidemics—Case of Vallisnieri—Case of Bacon—On
Cutaneous Diseases, Convulsions, Paralysis,  Epilep-
sy, &.c.—Observations of  Dr. Olbers.

LECTURE XXVII.....physical constitu-
               tion OF COMETS.
  Orbitual Motion of Comets—Number—Light—Ex-
planation of this—Theory of Herschel—Constitution
of Comets—Nebulosity—Nucleus—Tail—Cometa of
1811, 1680, 1769, 1744, 1843, 1B44.

 LECTURE XXVIII.....thunder storms.
   Of common Thunder-Clouds—Character and Elec-
tric Charge of Clouds—Discharge between the Clouds
and the Earth—Mutual Attraction or Repulsion of
Electrized Clouds—Characters of the upper and low-
er Surface of the Clauds—Negative Testimony re-
specting Thunder from an isolated Cloud—Cases of
Lightning from an isolated Cloud—A fresh Case re-
lated by M. Duperrey—Of Vtlcania Thunder-Clouds
—Lightning from the Aehes, Smoke, and Vapor of
Volcanoes—Origin—Of the Hight of Storm-Clouds
—Mode of Observation—Ascending Flashes of Light-
ning—Minor Limits of the Hight of Storm-Clouds—
Inefficiency of many recorded  Observations— rable
of Observations as collected  by Arago—Flash  *f
Lightning from a Cloud  upward—Of Lightning—
Varieties  of  Lightning—Zigzag Lightning—I'orked
Lightning—Sheet Lightning—Ball Lightning— Onthe
Speed of Lightning—Theory of Vision illustrated—
Experiments—Velocity of Lightning—Silent Light-
ning— Heat Lightning—Thunder Bursts— Of Lumin-
ous Clouds—Clouds themselves faintly Luminous-
Clouds visibly Luminous—Sabine's Observations—
Of Thmider—Rolling of Thunder—Duration and In-
tensity—Violent Thunder from Ball Lightning—Inter-
val between Lightning and Thunder—A case in which
they were almost  simultaneous—Thunder without
Lightning—Noise attendant on Earthquakes—Of the
Attempts to Explain the Phenomena of Thunder and
Lightning—Identity of Lightning and Electricity—
Undulatory Hypothesis—Ball Lightning and the In-
ferences to which it leads—Bituminous Matter ac-
companying a Case of Lightning Discharge—Expla-
nations of Silent Lightoinga—Observations of Silent
Lightnings—Arago's Suggestion for Observations—
Lightning hidden  by dense Clouds—Plaee of the
sound  of Thunder—Greatest Distance at which
Thunder is heard—Case of Distance beyond which
it was Inaudible—Distance at which  other Sounds
have been heard—Effects of Heat, Cold, Wind, &c—
On the Transmission  of Sound—Thunder heard
when no Cloud was Visible—Duration of an Echo—
Duration of the Roll of Thunder at Sea—Application
of tbe Theory to Zigzag Lightning—Means of obtain-
ing a Limit of the Length of a Flash.

LECTURE  XXIX.....the  latitudes asd
                longitudes.
  Definition of the Equator and Poles—Latitude of a
Place—Parallel of Latitude—Meridian of a Place—Lon-
  tude of a Place—Standard Meridian—Methods  of
  etermining Latitude  and Longitude Various—To
find the Latitude—Methods applicable in Observato-
ries—At Sea—Iladley's Sextant—To determine the
Longitude—How to find the Time of Day on Land—
At Sea—Use of Chronometers—Lunar Method  of
finding the Longitude —Apparatus provided at Green-
wich for giving the exact Time to Ships leaving the
Port of London—Method of determining Longitude
by Moon—Culminating Stars, &c.

  LECTURE  XXX.....theory  of colors.
   Refraction of a Ray  of Light—By  a Prism—The
Prismatic Spectrum—Decomposition of Liglft—New-
ton's Discoveries—Colors of the Spectrum—Brew-
ster's Discovery of three Colors—How three Colors
can produce the Spectrum—Colors of natural Bodisa
—How they are produced.

 LECTURE  XXXI.....the  visible stars.
   What occupies the Space beyond the Limits of the
Solar System—Wide Vacuity between this System
and the Stars)—The immense  Distance of the Stara
proved by the Earth's annual Motion—Observations
made at Greenwich—Bessel's Discovery of the Par-
allax—Distance of the Stars—Illustrations of the Mag-
nitude of this Distance—The .different Orders and
Magnitudes of the Stars—How accounted for—Why
those of the lowest Magnitude are most Numerous—
The Telescope unable to magnify them—Brightness
and Magnitude of  the Stars in Relation to the Sun—
Their Stupendous Magnitude—Application of thia to
tlie Dog-Star, &c.

LECTURE  XXXII.....water-spouts and
                 whirlwinds.
   Character and Effect of Water-Spouts—Difference
between Water and  Land Snouts—Land-Spout at
Montpellier—Land-Spout at Esclados—Columns of
Sand on Steppes of South Amerien—Meteors—Land-
Spout at Ohscjuvi.:—Conversion of a Storm into a
Land-Spout—Wafr-Spouts seen by Cnpt. Beechy—
Illustration of the Gyratory Motion of Water-Spouts
—Action of  charged Clouds on Light Bodies—Noise
attending Water and Land Spouts—Transition from
 direct to Gyratory Motion—Effect of Induction on
 watery Surfaces—Disappearance of Pools, &c. 
DR. LARDNER'S    LECTURES.
   LECTURE  XXXIII........matter  and  its
               physical properties.
  Unlimited Divisibility—Micrometric Wire—Method
  of making it—Thickness of a Soap-Bubble—Wings of
  Insects—Gilding  of Embroidery—Globules  of the
  Blood—Animalcules—Their Minute Organization—
  Ultimate Atoms—Crystals—Porosity—Volume—Den-
  sity—Quicksilver passing through Pores of Wood—
  Filtration—Heat—Contraction of Metal used  to re-
 store the Perpendicular to Walls of a Building—Im-
 penetrability of Air—Compressibility of it—Elasticity
 of it—Liquids not absolutely Incompressible—Exper-
 iments—Elasticity of  Fluids—Aeriform Fluids—Do-
 mestic Fire-Box—Inertia—Matter incapable of  spon-
 taneous Change—Impediments to Motion—Motion of
 the Solar System—Spontaneous Motion—Immateri-
 ality of the thinking and willing Principles—Language
 used to express Inertia sometimes faulty—Examples
 of Inertia, &c.  &c.

 LECTURE XXXIV.....elasticity of air.
   Exhausting Syringe—Impossible to produce a per-
 fect Vacuum—The Air-Pump—Baroweter Gauge-
 Siphon Gauge—Pump without Suction-Valve—Blad-
 der burst by Atmospheric Pressure—By Elasticity of
 Air—Dried  Fruit inflated—Fixed Air—Water raised
 by Elastic Force—A Pump cannot act in the absence
 of Atmospheric Pressure—Suction ceases when this
 Preasure is removed—Guinea and Feather Experi-
 ment—Cupping—Effervescing Liquors—Sparkling of
 Champagne, &c.—Presence of Air necessary for the
 Transmission of Sound—The Condensing  Syringe—
 The Condenser, &c. &c.

 LECTURE XXXV.....effects  of light-
                      ning.
   Effects of Lightning—The Sulphureous Odor devel-
 oped by Lightniny -Chemical Changes operated by
 Lightning—Nitric  Acid  formed by the Electric
 Spark; also, Ammonia and  Nitric Acid  produced
 during Thunder Storms—Fusion and Contraction of
 Metals—Observations of the Ancients—Franklin's
 cold Fusion—Masses of Metals melted by  Lightning
 —Vitrefactions  and Fulgurites—Facts collected  by
 M. Arago—Fulgurites—Recent Formation  of Fulgu-
 rites observed—Mechanical Effects—Instances of the
 Mechanical  Action of Lightning—Action is exerted
 in all Directions—M. Arago's Explanation of the Ef-
 fect as due  to Vaporization—Decompositions of the
 Natural Electricities of Bodies—Induction between
 the Clouds and  the Earth—Upward Flashes and Me-
 chanical Effects—Effects  of Conducting Bodies  on
 Lightning—Conducting Properties of Metallic Bod-
 ies—Lightning passing  along Conductors in Prefer-
 ence to  Non-Conductors—Protection  afforded  by
 Conducting  Bodies—Lightning selects  Conducting
 Bodies from among others—Lightning Conductors
 should descend to a humid Soil—Necessity of  Con-
 tinuity in a Conductor—Effects proceeding from the
 Surface of the Earth—Ascent or Ebullition of Water
 —Inundations from Subterranean Sources—Mosaic
 Account of the Deluge—Electrical State of the Atmo-
 sphere Favorable  to the Process of Barking Trees—
 Effect of Thunder on fermented Liquors, &c.—The-
 ory of such Effects—Flame appearing on the Ground
 —Not extinguishable by Water— Superposed Clouds
 not necessary to its Appearance—Stationary lumin-
 ous Appearance—Lightning rising from the Earth
 like a Rocket—Flames observed on exposed Points
 —Luminous Rain—Luminous Dust.

 LECTURE XXXVI....popular fallacies.
  Fallacious  Indications of Senses—Errors  of the
 Sense of Feeling—Erroneous Impressions of  Heat
and Cold—Explanation of these by the  Principle of
 Conduction—Why a Fan is cooling—Feats of the
 Fire-King explained—Horizontal Appearance of the
 Sun and Moon—Deceptive Oval Disk in the Horizon
—Deceptions of Vision, of Taste, of Smelling.

 LECTURE XXXVII.....protection from
                 lightning.
  Daager proportionate  to the Magnitude, not to the
 Frequency of the Evil—Ancient Methods of averting
Lightning—Persons in Bed not Secure, as some
think—Augustus's  Seal-skin Cloak as a Lightning
Protector—Influence of Color on the Electric Fluid—
Tiberius's Crown of Laurel as a Lightning Protector
  ■The Danger of taking Shelter beneath Trees—Fu-
tility of taking Shelter in Glass Cages—Metal about
the Person destroyed by Lightning—Metal Append-
ages to be laid aside—Part of a Room which is most
Safe—Lightning more  likely to discharge among a
Crowd than on a single Individual—Certain Individ-
uals are  comparative  Non-Conductors—Thunder-
Clouds have been Traversed with Impunity—Thun-
der-Storms below the  Place of Observation—Paea-
TONNEaaES,  or Lightning Conductors—Sparks-jr
Lightning Conductors  drain  off the Electricity of
Clouds—Frequent Occurrence at Sea—Influence of
Elevation of a Paratonnerre—Experimental Illustra-
tipn—Electric Kites—Captive Balloons—Pointed and
blunt Conductors—Quantity of Lightning  drawn
down by a Conductor—Mr. Harris's Conductors for
Ships—Lightning dees  not always strike the highest
Points—Lightning Conductors—Charcoal Beds to re-
ceive the Base of the Conductor—Conductors of Met-
allic Wire—Rope—Conductors  for  Powder Maga-
zines—Efficacy  of Conductors—Artificial Means of
producing the Electrical Odor—Chemical Changes—
Fusion—Fulgurites—Mechanical  Effects—Effects of
Conducting Bodies, &c. &c.

    LECTURE XXXVIII.....magnetism.
  Magnetic Attraction and Polarity—Meridian, Varia-
tion—Dip of the Needle—Magnetic Attraction known
to the Ancients—Invention of the Mariner's Compass
—Discovery of the Variation—Tables  of Variation
constructed—Robert Norman  discovers  the Dip—
Invention of the Dipping Needle—The Variation of
the Variation  discovered—Influence  of Magnets on
Soft Iron—Construction of Artificial  Magnets—Mag-
netism imparted to Iron by the Earth—Laws of Mag-
netic  Attraction discovered by Coulomb—Methods
of making Artificial Magnets—Influence of Heat on
Magnetism—Changes  of the Variation—Advance-
ment  of Magnetic Geography—Magnetic Equator—
Magnetic Poles, &c. &c.

LECTURE  XXXIX..-electro-magnetism.
  Electro-Magnetism very recently discovered—Oer-
sted's Experiments at Copenhagen—The Law ac-
cording to which the Needle is deflected—The Law
of Attraction  and Repulsion of Electric Currents—
Supposes  Electric Currents circulating round  the
Globe—Arago shows that the Conducting Wire  has
Magnetic  Properties—Needles magnetized by  the
Electric Current—Faraday's Researches—Rotation
imparted  to Mercury by means of the Magnet  and
Electric Current—The  Multiplier and Galvanometer
—Researches  of M. de la Rive—Magnetizing Power
of the Current at different Distances—The undulato-
ry Theory of Electricity similar to that of Light—
Thermo-Eleclricity—Experiments with Antimony and
Copper—Researches—Oersted and Fourier construct
a Thermo-Electric Pile— Becquerel decomposes Wa-
ter with such  an Instrument, &c. &c.

  LECTUR,E XL.....the thermometer.
  Advantages  of Mercurial Thermometer—Method
of constructing one—To purify the Mercury—Form-
ation of the Tube—To  fill the Tube—Determination
of the freezing and boiling Points—Modes of Gradu-
ation—Alcohol Thermometers—Difficulty of fixing
the  boiling Point—Usefulness of the Thermometer—
History of its Invention—Methods of comparing
Scales of different Thermometers.

LECTURE   XLI.......atmospheric  elec-
                   tricity.
  Electricity of the Atmosphere in clear Weather—Con-
nection between Electricity and Meteorology—Appa-
ratus for observing the Electricity of the Atmosphere—
Occasional use of the Galvanometer—The ordinary
State of the Atmosphere—Theory of the Origin of At-
mospheric Electricity—Probable Influence «f Fric-
tion—Diurnal  Variation of  the Electricity—Maxima
and Minima at a given Parallel—Schubler's Observa-
tions—Influence of particular  Localities, Buildinga, 
DR.  LARDNERS LECTURES,
 &c.—No satisfactory Explanation yet given of the
 Variations—Becquerel's Explanation of the Phenom-
 ena of Variation—Distribution of Electricity of the
 Air— Negative State of the Earth—Electricity of tlie
 Air in clouded Weather—Schiibler's  Observations—
 Table of Observations explained, &c. &c.

     LECTURE  XLII.....evaporation.
   Erroneously ascribed to Chemical Combination—
 Takes place from the Surface—Law discovered by
 Dalton extended to all Liquids—Limit of Evapora-
 tion conjectured by  Faraday—Hygrometers—Vari-
 ous Phenomena explained by Evaporation—Leslie's
 Method of  Freezing—Examples in the useful Arts—
 Methods of Cooling by Evaporation—Dangerous Ef-
 fects of Dampness—Wollaston's Cryophorus—Pneu-
 matic Ink-Bottle—Clouds—Dew, &c. &c.

 LECTURE  XLIII___conduction of heat.
   Conducting Powers of Bodies—Liquids  Non-con-
 ductora—Effect of Feathers and Wool on Animals—
 Clothing—Familiar Examples.

 LECTURE  XLIV......relation of  heat
                 AND LIGHT.
   Probable Identity of Heat  and Light—Incandes-
 cence—Probable Temperature of—Gases cannot be
 made Incandescent—The Absorption and Reflection
 of Heat depend on Color—Burniug-Glass—Heat of
 Sun's Rays—Heat of Artificial Light—Moonlight—
 Phosphorescence.

 LECTURE XLV.....action and reaction.
   Inertia in a single Body—Consequence of Inertia in
 two or more  Bodies—Examples—Motion  not esti-
 mated by Speed or Velocity alone—Examples—Rule
 for estimating the  Quantity of Motion—Action  and
 Reaction—Examples of—Magnet and Iron—Feather
 and Cannon-Ball impinging—Newton's Laws of Mo-
 tion.
 LECTURE  XLVI.......composition  and
           resolution of force.
  Motion and  Pressure—Force—Attraction—Paral-
 lelogram of Forces—Resultant—Components—Com-
 nosition of Force—Resolution of Force—Illustrative
 Experiments—Composition of Pressures—Theorems
 regulating Pressures also regulate  Motion—Boat in a
 Current—Motions of Fishes—Flight of Birds—Sails
 of a Vessel—Tacking—Equestrian Feats, &c. &c.

 LECTURE  XLVII.....center of gravity.
  Terrestrial Attraction the combined Action of Par-
 allel Forces—Method of finding the Center of Gravity
 —Line of Direction—Globe—Oblate Spheroid—Pro-
 late Spheroid—Cube—Straight Wand—Flat Plate—
 Triangular Plate—Center of Gravity not always with-
 in the Body—A Ring—Experiments—Motion and Po-
 sition of the Arms and Feet—Effect of the Knee-joint
 —Positions  of a Dancer—Porter under a Load—Mo-
 tion of a Quadruped—Rope-Dancing—Center of
 Gravity of two Bodies separated from each other—
 Mathematical  and  Experimental  Examples—The
 Conservation of the Motion of the  Center of Gravity
 —Solar System—Center of Gravity sometimes called
 Center of Inertia, &c. &c.

 LECTURE  XLVIII.......the lever  and
               wheel-work.
  Simple Machine—Statics—Dyn amies—Force—
 Power—Weight—Lever—Cord—Inclined Plane—
 Arms—Fulcrum—Three kinds of Lever—Crow-Bar
—Handspike—Oar—Nut-Crackers—Turning-Lathe—
 Steelyard—Rectangular Lever—Hammer—Load be-
tween two Bearers—Combination of Levers—Equiv-
alent  Lever—Wheel  and Axle—Thickness of  the
Rope—Ways of applying tbe Power—Projecting Pins
—Windlass—Winch—Axle— Horizontal Wheel—
 Tread-Mill—Cranes—Water- Wheels— Paddle-Wheel
—Racket-Wheel—Rack—Spring of a Watch—Fusee
—Straps or Cords—Examples of—Turniiis Lathe—
Revolving Shafts—Spinning Machinery—Saw-Mill—
Pinion—Leaves—Crane—Spur-Wheels—Crown-
wheels—Beveied Wheels—Hunting-Cog—Chronom-
eters^—Hair-dpring—Balance-Wheel, &c.
      LECTURE XLIX___the pulley.
   Cord—Sheave—Fixed Pulley—Fire Escapes—Sin-
 gle Movable Pulley—Systems of Pulleys—Smeaton's
 Tackle—White's Pulley—Advantage ot—Runner—
 Spanish Bartons.

 LECTURE L.-.the inclined plane, wedge
                 AND SCREW.
   Inclined Plane—Effect of a Weight on—Power of—
 Roads—Plane sometimes  moves under the Weight
 —Wedge—Sometimes formed of two Inclined Planes
 —More powerful as its Angle is Acute—Where used
 —Limits to the Angle—Screw—Examples.

       LECTURE LI---ebullition.
   Process of Boiling—Vaporization and  Condensa-
 tion—Latent Heat of Steam—Experiments of Black—
 Effect of Atmospheric Pressure on  Boiling Point—
 Relation  between the Barometer and the  Boiling
 Point—Effect of the Altitude of the Station  of the Boil-
 ing Point—Elasticity of Steam—Its Lightness—Effect
 of the Compression of Steam without Loss of Heat—
 Steam cannot be liquified by mere Pressure—Boil-
 ing Points and Latent Heat of other Liquids—Con-
 densation of Vapor—Principle of the Steam-Engine—
 Nature of Permanent Gases—Examples of the Appli-
 cation of the Properties of Steam.

      LECTURE  LII....combustion.
   Flame produced by Chemical Combination—Sup-
 porters of Combustion  and Combustibles—Oxygen
 chief Supporter—Heat of Combustion—Flame—Its
 illuminating Powers—Combustion without Flame—
 Property of spongy Platinum—Table of Hoat evolved
 in Combustion—Theory of Lavoisier—Of Hook and
 others—Electric Theory.

 LECTURE L1II.....how to observe  the
                   heavens.
  Interesting Nature of the Subject—Diurnal Rota-
 tion— Circumpolar Stars— Ursa Major—Forma of the
 Constellations—The Pointers—The  Pole-Star— Cas-
 siopeia—Capefta.—The Swan—Equatorial  Constella-
 tions— Orion—Sirius, or the Dog-Star—Aldebaran—
 Procyon—Auriga—Columba—Herschels Observa-
 tions on Sirius—Dr.  Wollaston's Observations—As-
 pect of the Heavens at different Seasons of the Year
 —Uses of the Celestial  Globe—To ascertain the As-
 pect of the Heavens on any Night, at any  Hour—Ef-
fect of the Telescope on Fixed Stars—Relative Bright-
ness of the Stars—Theory of Telescopes—Descrip-
 tion of the Micrometer, &c. &c.

 LECTURE  LIV---the stellar universb.
              (First  Lecture.)
  Range of Vision—Auernented by the Telescope-
 Periodic Stars—Examples of this Class—Various Hy-
 potheses to explain these Appearances— Temporary
 Stars—Remarkable Examples of this Class—Deuble
Stars—Their vast Number—Telescopic  Views  of
them—Researches of Sir W. Heschel—Extension of
 Gravitation to the Stars—Their elliptic Orbits discov-
 ered—Effects of double and colored  Suns-Proper
Motions of tlie Stars—Probable  Motion of the Solar
 System—Analysis of its Effects—Motions of the
 Stars, &c. &c.

 LECTURE LV---the stellar universe.
              (Second Lecture.)
  Form and Arrangement of the Mass of Visible Stars
TrVf "*; Herschel's Analysis of the Heavens-The
Milky Wny-The vast Numbers of Stars in it-Neb-
ulas and Clusters-Great Nebula in  Orion—Megal-
 lame Clouds-Planetary Nebulas-Vast Number of
 Nebula—- Herschel's Catalogue—Structure  of the
Universe-Laplace's Nebular Hypothesis—Examina-
tion of us moral Tendency.

   LECTURE  LVI---the steam-engine.
               (First Lecture.)
  The Steam-Engine a Subject of Popular Interest-
Effects of Steam-Great Power of Steam-Mechan-
ksJI Properties of Fluids-Elasticity of Gases-Etlecta
of Heat-Savery's Engine— Boilers andtheir Append- 
DR.  LARDNER S  LECTURES.
ages—Working Apparatus—Mode of ©peration—De-
fects of Savery's Engine—Newcomen and Cawley's
Patent—Accidental Discovery of Condensation by In-
jection—Potter's Invention of the Method of Work-
ing the Valves—His Contrivance improved by the
Substitution of the Plug-Frame.

  LECTURE  LVII.....the steam-engine.
              (Second  Lecture.)
  Mechanical Force of Steam—Watt finds Condensa-
tion in the Cylinder incompatible with a due Econo-
my of Fuel—Conceives the notion of Condensing out
of the Cylinder— Invents the  Air-Pump—Substitutes
Steam Pressure for Atmospheric Pressure—Invents
the Steam Case or  Jacket—His Models—Difficulties
of bringing the Improved Engine into Use—Watt em-
ployed by Roebuck—His Partnership—His first Pa-
tent—His Single-Acting Engine—Discovery  of the
Expansive Action of Steam—Extension of the Steam-
Engine to Manufacmres—Attempts of Papin, Savery,
Hull, Champion, Stewart, and Wasbrough—Watt's
Becond  Patent-Sun-and-Planet Wheels—Valves of
Double-Acting Engine.
  LECTURE  LVIII___the steam-engine.
               ( Third Lecture.)
   Methods of Connecting the Piston-Rod and Beam
in  the Double-Acting Engine—Rack and  Sector-
Parallel Motion—Connection of Piston-Rod and Beam
-Connecting-Rod and Crank—Fly-Wheel—Shuttle-
Valve— Governor—Construction and  Operation of
the Double-Acting Engine—Eccentric—Cocks and
Valves—Single-Clack Valves—Double-Clack Valves
—Conical Valves—Slide Valves—Murray's  Slides—
The D Valves—Seaward's Slides—Cocks—Pistons—
Cartwright's Engine.
   LECTURE LIX.....the steam-engine.
               (Fourth Lecture.)
   Analysis  of Coal—Process of Combustion—Heat
evolved in it—Form and Structure of Boiler— Wagon-
Boiler— Furnace—Method of Feeding it—Combustion
of Gas in Flues—Williams's Patent for Method of
Consuming unburned Gases—Construction of Grate
and Ash-Pit—Magnitude of Heating Surface of Boiler
—Steam-Space and Water-Space in Boiler—Position
of Flues—Method of Feeding Boiler—Method of In-
dicating the Level of Water in Boiler—Lever Gauges
—Self-Regulating Feeders—Steam-Gauge—Barome-
ter-Gauge—Watt'a Invention of the Indicator—Coun-
ter—Safety-Valve—Fusible Plugs—Self-Regulating
Damper—Brunton's Self-Regulating Furnace—Gross
and Useful Effect of an  Engine—Horse-Power of
Steam-Engines—Table exhibiting  the  Mechanical
Power of Water converted into Steam at  various
Pressures—Evaporation Proportional to Horse-Power
—Sources of Loss of Power—Absence of good Prac-
tical Rules for Power—Common Rules  followed by
Engine-Makers—Duty  distinguished from Power-
Duty of Boilers—Proportion of Stroke to Diameter of
Cylinder—Duty of Engines.

   LECTURE LX.....the steam-engine.
               (Fifth Lecture.)
  Railways—Effects of Railway Transport—History
of the Locomotive Engine—Construction of Locomo-
tive Engine by Blinkinsop—Messrs. Chapman's Con-
trivance—Walking Engine—Mr.  Stephenson's  En-
gines at Killingworth—Liverpool  and  Manchester
Railway—Experimental Trial of the " Rocket," " Sans-
pareil," and "Novelty"—Method of Subdividing the
Flue into  Tubes—Progressive  Improvement of Lo-
comotive  Engines—Adoption of Brass  Tubes—De-
tailed Description of the most Improved Locomotive
Engines—Power of Locomotive Engines—Position
of the Eccentrics—Pressure of Steam in the Boiler—
Dr.  Lardner*s Experiments in  1838—Resistance to
Railway Trains—Dr. Laidner's Experiments on the
Great Western Railway—Experiments on Resistance
—Restrictions on Gradients—Compensating Effect of
Gradients—Experiment with the "Hecla"—Disposi-
tion  of Gradients should be Uniform—Methods of
surmounting Steep Inclinations.
  I0P The above Work was originally published in Fourteen Numbers or Parts, and sold at the
extremely low price of 25 cents per Number.  Any of the Numbers can still be purchased.  The
entire Work is now completed and  sold in two large octavo volumes of  about 600 pages each,
well bound in full cloth, illustrated by 380 Engravings, and sold at $4 SO.
  Ep= District School Libraries can order these Lectures through any of the Booksellers or Coun-
try Merchants.  Parents, Teachers, Superintendents and Trustees of Common Schools, Farmers,
Mechanics, and all, indeed, who have  any desire  to increase their store of useful information on
the subjects embraced in these volumes, are earnestly entreated to examine this Work before
they throw away their money on the trash, or even worse than trash, that is now so rapidly inun-

dating the country.
  From among the  numerous Recommendatory Notices which  the Publishers received during

the progress of the publication, we have only room to give the following
From D. Meredith Reese, A. M, M. D., ,Superin-
  tendent of Common Schools in the City and County

  of Neto- York.       New.Yoek, Oct. 20th, 1845.
MflBsrs Gbeeley & McElkath :
  G^Omen: I have examined the Popular Lectures
of J)T. L?kdneh,  on Science and Akt, with much
.atisfaction and  take pleasure in  expressing  the
"pinion in" you are doing a valuable service to the
People of our common country by their publication
^especially by issuing them .n numbers, and at so

ChToPpopula'rize Science and  cheapen Knowledge
mus° be regarded by the philanthropist as worthy of
the mighuest minds of the age. and  to be successful
ns^ch efforts, constitutes their authors public bene-
factors   These Lectures of Dr. Lardner are ad-
dressed to  the common  mind, and though treading
   T,hn loftiest of the Natural  Sciences, are so plain
"nTpitKXple  and attractive, that all who
can read may readily profit by their .nstruct.ons. The




Jfomate Iheir own happiness and usefulness.
  I could wish that they were found in every School
Library, to which their scientific accuracy and nu-
merous moral reflections upon the wonderful works
of God should be esteemed no 6mall commendation.
But they should  be found in every work-shop in the
land;  for Science and Art are here exhibited in their
true relations; and the working men of our country
would find here  both entertainment and instruction,
calculated to improve alike their intellects and their
morals.                          D. M. Reese.
                         Albany, May 5,1846.
Gbeeley& McEleath:
  Gentlemen: I cordially and cheerfully concur with
my friend, Dr. Reese, in the high appreciation which
he places on your edition of Dr. Lardner'a Lecturea,
and have no hesitation in recommending them as a
most valuable acquisition to our School Libraries.
                   Saml. S. Randall,
                       Dep. Supt. Com. Schools.
  " These  publications  are admirably adapted to in-
terest and instruct the general reader."
                            [Norwich Gleaner.
  "No man has  succeeded better in giving popular
interest to abstruse subjects than Dr. Lardner."
                             [ Worcester Mgis. 
EWBANK'S   HYDRAULICS   AND   MECHANICS.
                                OPINIONS  OF  THE  PRESS.

  This is a highly valuable production, replete with novelty and interest, and adapted to gratify equally the his-
torian, the philosopher, and the mechanician, being the result of a protracted and extensive research among the
arcana of historical and scientific literature.  Mr. Ewbank's wqrk can not be too widely circulated. It w an
elegant " Table-BooK," suitable to all person*—to the ordinary reader, who is  anxious to acquire useful knowl-
edge, as well as to the theoretical and practical connoisseur  in hydraulics.  Hundreds of impressive biographi-
cal and historical anecdotes, generally unknown, might be  quoted as proofs of the multifarious intelligence which
Mr. Ewbank has amassed for the edification of those who may study his richly-entertaining volume. Vv e know
not a compilation specifically designed to exhibit that mechanical philosophy which appertains to common, do-
mestic, and social life, with the public weal, to which the attention of youth can be directed with equal amuse-
ment and beneficial illumination as to Mr. Ewbank's acceptable  disquisitions.  Therefore we earnestly recom-
mend his volume to their study in preference to the perusal of those  fantastic and pernicious  fictions which
pervert the imagination, and deteriorate the mind, and  corrupt the  morals of the thoughtless myriads who
"feed on those ashes."—Nutionul Intelligencer.
  It throws more light upon the progress of mankind from the earliest ages, in the useful arts, than  any volume
we have ever seen.—Alexander's Messenger.
  The only volume ever published embracing an account of all the contrivances employed in different ages by
•different people for raising water.  It is really one of the most  remarkable publications connected with me-
chanical philosophy that has ever fallen under our observation.—Merchants' Magazine.
  We have long known that Mr. Ewbank was preparing  this work for the press, and have looked for its publi-
cation with a conviction that we should derive much valuable information from its perusal; an expectation that
has been fully justified by the result  His  work is not one which can fall still-born from the press, as it is not
one of those ephemeral productions that must sell at the  moment or never.—Journal of the Franklin Institute.
  An interesting work of science.  The title will furnish  the reader a good general notion of the matter of the
book, but not of the clearness, method, precision, and ease of the manner of it.  We believe there is no work
extant which treats of the specific topics which he has  chosen—none we are certain which describes it with
more fullness of argument and illustration.—Democratic Review.
  All classes, as well the farmer and professional man as the artist and engineer, will rise from a careful peru-
Bal of Mr. Ewbank's book wiser and better.— U. S. Monthly Review.
  It contains more valuable, curious, and interesting information  than  can be  found in any volume ever pub-
lished on the subject, and is a work which commands the attention, and should be placed upon the shelf, of
every gentleman's library, and in every college and academy.—iV. Y. Sun.
  A splendid book. We are inclined to believe that it will be one of the most curious and interesting works that
have issued from the American press for many years.—_V. Y\ Tribune.
  It possesses great interest, not only for mechanicians, engineers, and men of science, but for intelligent read-
ers generally.—Philadelphia Enquirer i, National Gazette.
  A rich  mine for exploration by the practical  or  theoretical engineer, as well as by those who like to make
themselves acquainted with the developments of mechanical ingenuity.—.v.  V. Commercial Advertiser.
  This large and beautifully-printed octavo is probably the most  valuable volume that the publishers have pre-
sented to the public during the past year.—N. Y. Courier If Enquirer.
  It is a scientific work, but commends itself not to tlie scholar only, but to the mechanic and  general reader,
for it is perfectly free from pedantry and learned affectation.—Boston Daily Times.
  An Encyclopedia of mechanics.  It is richly illustrated, full of curious information, and every way worthy,
by its copious knowledge and its incentives to curiosity, not  only to a place in every gentleman's library, but
what is more, to one on the shelves of every district school library in tlie state.— Union.
  A thick volume of nearly fiOO pages ; but let no reader be dismayed by its size, for the  author says  with a
good deal of truth, that in the annals of niechfinics are to be found incidents as agreeable and exciting in the ir
nature as anything that can lie realized by the imagination.   We  are not sure that a single corner of the world,
or recess of history, has escaped his laborious researches.—.V. Y. Evening Post.
  Whoever rejects this book from the supposition that it is a dull detail of machinery and the various applica-
tions of the mechanic powers, will be guilty of trreat injustice to  the author.  It is  one of the most entertaining
books we have ever met with, on a scientific subject.  It is full of interesting historical and well-written de-
scriptive matter, interspersed with appropriate quotations from old writers, enough almost to give  it the title of
The  Poetry of Mechanics.—Boston Courier.
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  It entitles him (the author) to take rank at once with the very best writers in this department of literature
whether ancient or modem.   Quite as entertaining as Beckman, he exceeds him immeru-urably in practical Mse-
fulness;  and while ainimg, like Ferguson, at a popular style, he brings to his aid a  liveliness  of fancy depth of
feeling, and eloquence of  expression, to which Ferguson was  a  stranger. We have seldom seen a volume so
absolutely  crammed with useful information.—London Mechanics' Magazine.
  A compressed library.  On the subject here treated, tomes have been multiplied to an amazin" extent Their
essence is given in this volume.   In short it is such a work of labor and original research as we rarely  see  It
ia an acceptable contribution to the literature of mechanical science and practical engineering   It ia the kind
of book which every mechanic or inventor ought to consult— London Athenaum.
  This work is  eminently entitled to be called a history of the human race, since it carries us forward from one
stage of  advancing civilization, beginning  -.nth the rudest and most simple efforts of ingenuity to the almost
immeasurably superior wonders of our own day.. . . Whether viewed as a purely philosophical work? or as a
comprehensive text book for mechanics and inventors, Mr. Ewbank's book is equally valuable.  The mass of in-
formation it contains is unusually great, and the immense variety of machines which it describesTare Mutated
with about 300 engravings.   It is capable of saving infinite trouble and mortification to  ta£nto"     We have
seldom seen a more instructive and amusing work.-From the Surveyor, Engineer, and Architect's Journal
   Phis work exhibits the results of reading and research seldom manifested in these days  of book-matin'

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                                     GREELEY & McELRATH, Tribune Buildings, Publisners, 
                       POPULAR  LECTURES  ON

               ASTRONOMY,
                               BY  M.  ARAGO;

WITH  ADDITIONS  AND   CORRECTIONS,
                           BY  DR.  LARDNER:
ILLUSTRATED BY  FIFTY-THREE  DIAGRAMS OR  ENGRAVINGS.
                        PUBLISHERS'  PREFACE.

  To all who are conversant with the existing state of Astronomical Science in Europe, it la well known
that In addition to the regular duties of his ofhce as Royal Astronomer of France, M. Arago haa been in the
practice of delivering each season, at the Observatoire, a Course of Lecturea of a  popular kind, which are
attended by all classes of well-informed  persona, including ladies in considerable  numbers.  Theae dis-
coursed are given extemporaneously in tbe strictest sense of the term, and in etyle and character bear a
close analogy to those delivered by Dr. Lardner in this country within the last few years. It does not ap.
pear that M. Arago ever designed their publication, nor that he ever even committed them to writing. A
person employed by one of tbe Brussels publishers reported tbem, and the publication reputed to be
M. Arago's Lecturea ia nothing more than this report wbich though it could not be legally published or
circulated in France, obtained through the Belgian booksellers  and their correspondents  an extensiva
Illegal circulation in that country.  A translation of thia report was circulated largely in England.
  The publishers of the preaent volume,  being aware that errors of a more or leaa  important kind must,
under such circumstances, have prevailed in the original Belgian edition, and still more in the English trans-
lation, and that omissions and chasms must have required to be filled up by some  person conversant with
tbe Science, and capable of writing upon it  in an easy and familiar atyle, applied to Dr.  Lardner, and
induced him to revise  the reported Lectures, and to add  to them auch topics as might appear desirable to
give them increased utility.  The result of thia arrangement haa been the present volume.
  Dr. Lardner desires it to be understood tbat he ahould not have felt himself justified in interpolating
any work, however elementary, published with the actual sanction of M. Arago's  name.   But it being
understood, and indeed manifested by unequivocal internal evidence, that the Belgian report waa unauthor-
ized and unauthentic, and the circulation  of some translation of it in this country being rendered inevitable
by the very popularity of ita reputed author, it was better that a carefully revised copy ahould be publiahed
than a mere reprint of the English translation of the imperfect Belgian report
CONTENTS
                 LECTURE I.
  General Lawa of the Reflection of Light—General
 Laws of the Refraction of Light—Lenses—Refract-
 ing and Reflecting Telescopes—Structure of the Eye.

                 LECTURE II.
  Hiatory of Aatronomy—Preliminary Ideas—Defini-
 oitiona—Capricornus  (Caper)—Aquarius—Pisces—
 Aries—Taurua—Gemini—Cancer—Leo—Virgo—Li-
 bra—Scorpio—Sagittarius.

                LECTURE HI.
  Aspect of the Heavena—Apparent Motions of the
 Heavenly Bodies.

                LECTURE IV.
  The Fixed Stara.

                LECTURE V.
  Dletancea of the Planeta—The Sun—Phyalcal Con-
 •titution of the Sun—The Moon—Physical Constitu-
 tion of the Moon.

                LECTURE VI.
  Mercury—Physical Constitution of Mercury—Ve-
 nus—Appearance of Venus aa she moves  round the
 Sun—Physical  Constitution of  Venus.  Superior
 Planeta: Mars—Physical Constitution of Mara—The
 four Teleacopic Planeta: Juno, Ceres, Pallas, Vesta.

                LECTURE VII.
  Jupiter and his Satellites—Physical Conatitution of
 Jupiter—Saturn, hia Ring and hia Satellites—Her-
schel, or Uranus, and his Satellites.
               LECTURE VI1L
  Distances, Diameters, Volumea, &c. of the Planets
—Kepler'a Laws—Universal Attraction—Of the
Masses of tbe Planeta.
                LECTURE IX.
  Figure of the Earth—Dimensiona of the Earth—
The Earth's Motion—Diurnal Rotation of the Earth
—Annual Motion of Earth.
                LECTURE  X.
  Inequalities of the Moon and of the Earth.
                LECTURE XI.
  Comets— Halley'a and  other  Comets—Phyalcal
Constitution of Comets.
               LECTURE XH.
  Eclipses of the Moon—Eclipses of the Sun.
               LECTURE XHI.
  The Tidea.
               LECTURE XIV.
  Determination of Latitude and Longitude.
               LECTURE XV.
  The Atmosphere—Of the Moon in the Horlxon—
The Harvest Moon.
               LECTURE XVI.
  The Seasons and the Days—The Earth's Tempera-
ture.
               LECTURE XVIL
  The Calendar.
                 APPENDIX.
  Table of the Constellationa, with the Number ei
Stara in each, aa far as those of the sixth magnitude-
Summary.
  1^ The above work is neatly printed, and well done up in paper covers, and sold at the
tow price of 25 cents.   Five copies will be mailed to any part of the United 8tates for $1.

               GREELEY & McELRATH, Publishers, Tribune Buildings, New-York. 
    HYDRAULICS   AND   MECHANICS.

A Descriptive and Historical Account of Hydraulic and other Machines for
   raising Water, ancient and modem;  with observations on various subjects
   connected  with  the  Mechanic Arts, including the Progressive Develop-
   ment of the Steam-Engine.  Descriptions of every variety of Bellows, Pis-
   ton, and  Rotary Pumps,  Fire-Engines, Water-Rams," Pressure-Engines,
   Air-Machines, Eolipiles, &c.   Remarks on Ancient Wells, Air-Beds, Cog-
   wheels,  Blowpipes,  Bellows of various People, Magic  Goblets, Steam
   Idols, and  other  Machinery of Ancient Temples.   To  which are  added
   Experiments on Blowing and  Spouting Tubes, and other original Devices.
   Nature's Modes  and Machinery for raising Water.  Historical Notice!
   respecting  Siphons, Fountains, Water  Organs, Clepsydrae, Pipes, Valve*,
   Cocks, &c.   In Five  Books.

                    BY   THOMAS  EWBANK.

         ILLUSTRATED   BY   300  ENGRAVINGS.
  This volume, on the various machinery connected with the raising of water, is a very interesting
production ; not only to the Experimental Philosopher, the Mechanician, and the Operative Trades-
man, who are engaged in the researches and work combined with the  objects specified in the
Treatise, but  also to every ordinary reader who is solicitous to enlarge his general informa-
tion, and who wishes to combine amusement with the topics which attract  his attention.
  It is impossible in this concise notice, to detail a minute syllabus of a book, the mere topical
index of the contents of which occupies nearly eight pages, numbering about one thousand dis-
tinct articles; but a  general view is presented, from which the nature and value of the disser-
tation can easily and correctly be estimated.
  The first book, which is subdivided into eighteen chapters, comprises a narrative of the various
" Primitive and Ancient  Devices for Raising Water," which  are exemplified by sixty-seven en-
graved specimens of their diversified contrivances.   This  is not merely a dry philosophical
comment, for there are many episodes  commingled with it  of a peculiarly  interesting charac-
ter, of which the preliminary remarks on  the historical accounts of warriors, and the section.
in chapter sixteen, on  the " Flattery  of Despots by Men of Science," may distinctly be mentioned/
  The second book, which includes seven chapters, describes the " Machines for Raising Water by
the Pressure of the Atmosphere."  With this part are incorporated thirty engravings, delineating
the chief inventions which have been used in that department.
  The third book, containing nine chapters, develops  the " Mechanics  for Raising Water by
Compressure, independently of Atmospheric Influence," with  sixty-nine pictorial representations
of bellows, pumps, and fire-engines.  The  discussions respecting water-works and fire-engines
are full of instruction, and combine more information upon those important  topics than can be
found, it is believed, in any other work that ever has been published.
  The fourth book is extended to nine chapters, and displays the " Machines for Raising Wa-
ter, chiefly of Modern Origin, including Early Applications  of Steam for that Purpose," witK
thirty-one engravings. This portion of the volume is very racy, especially the details concert
tag the Altars and Heron's Spiritalia, with the introductory paragraphs to chapter three, from
page^381 to 391, and the notice of  the Eolipilic  Idols.
  The fifth book^ which  also comprises nine chapters, with eighty-four engravings, unfolds the
"Novel Devices for  Raising Water, with  an Account of Siphons, Cocks, Valves, Clepsydrae,"
&c.,the seventh chapter of which, on Fountains, condenses a large quantum of information upon
that cooling and refreshing topic, which is followed by an  attractive elucidation of  hydraulic
organs.                                                                   J
  An Appendix, with five engravings, supplies some additional explanatory facts; and to  the
whole is subjoined a comprehensive index of all the principal subjects that are embodied in
those pages.

   In addition to  the above, the present edition contains a Supplement of over
thirty pages, on  ANCIENT EOLIPILES, with some curious illustrations.
   The entire work, with an Illustrated  Titlepage, will cost but half the pries
of the previous editions.

   V&" The above work is now publishing in EIGHT PARTS or numbers,
at 25 cents  each.          GREELEY & McELRATH, Publishers,

                                            Tribune Buildings, New York.