BRIEF EXPOSITION THE SCIENCE sm«xt&Erx and to light, the third. Thus the illustrations of the three imponderable agents, whose existence is gene- rally admitted by chemists, will be exhibited in imme- diate succession, and the diversity of their features rendered more striking by their proximity. There are additional reasons for giving precedency to these imponderables. There is no other science which stands so much by itself, as that of electricity, or which requires so little preliminary knowledge to render it intelligible. This remark applies more par- ticularly to that portion of the science, which is necessarily first treated of; being usually designated as mechanical, in contradistinction to Voltaic electri- city. The same remarks are to a great extent appli- cable in the case of caloric, and that of light; and I shall treat of these principles in succession next to electricity, not only in obedience to considerations which have been stated, but on account of the interest- ing illustrations with which, in treating of caloric, we are enabled to allure the attention of beginners, with- out reference to subjects yet untaught, or the use of agents of which they are ignorant. CONTENTS, Pago 1 History of Electricity - Electricity experimentally illustrated - - - 4 Order pursued hi the experimental illustration of Elec- tricity _..----- 5 Generic description of the Electrical Machine - - 5 1.—Description of an electrical plate machine - - -. - 0 2.—Electrical machine with a piate four feet in diameter - - 7 3.—Engraving and description of an electrical cylinder machine - - 7 Of the usual means of producing Electricity - - 7 4.—Experimental illustration ------- 8 Of the communication of Electricity - - - 8 5.—Experimental proofs that electricity does not pass from one part of an electric to another, through or by means of an electric - - 9 6.—Peale's experiment - - - - - - !) 7.—Modification of Peale's experiment - - - - - 10 8.—Additional illustration ,------11 9.—Experimental proofs that metals, charcoal, moisture, flax, or hemp, are conductors of electricity, and that sulphur, resins, glass, silk, and wool, are non-conductors - - - - - - - II Of different kinds of Electricity - - - -12 10.—Description of Bennet's gold leaf electrometer - - - - 13 11.—Experimental illustrations - - - ... - 13 Of Electric Poles.—Of Electric Circuits - - - VS Means of accumulating Electricity - - 15 12.—Experimental illustrations - - . - - -10 VS.—Coated pane ........ ig ]4.—Of the Leyden jar ....... 17 15.—Of the common discharger - - - - - -17 1(3.—A charge is imparted, equally well, by the contact or communication of either coating with either conductor - - - - - 18 17.—Experimental proofs that the different surfaces of a charged electric are oppositely electrified - - '- - - - - 19 18—Chime of bells ........ 19 Metallic coatings of use in conveying the charge—but it does not reside in them --------- 20 !9.—Pane with moveable coatings - - - - - 20 * 20.—Glass vessel so situated that water is made to perform the same office as metallic coatings in the Leyden phial; illustrating the original ex- periment of Cuneus and Mushenbrocck - - - 21 21.—Experimental demonstration that the charge of a Leyden jar does not reside in the coatings - - - - - - - 21 Of Electrical Batteries.....22 22.—Of an electrical battery of '32 jars, each 13 inches in height, and 5 inches in diameter """----- 23 23.—Description of Henley's universal discharger - - - - 23 24..—Battery discharger for deflagrating wires • ' - - - 24 VIII CONTENTS. Pago Of Electrical excitement by induction - - - 25 Jo.—Apparatus for the illustration of electrical induction - - - 25 '26.—New apparatus for the illustration of electrical induction - - 25 Means of detecting or measuring Electricity - - 27 'J7 —Description of the condensing electrometer - - - - 28 28.—Description of the single leaf electrometer - - - - 28 29.—Description of Henley's quadrant electrometer - - - - 29 29g.—Of Coulomb's electrometer - - - - - - 30 Of the effects of Electricity - - - - - 31 Of Electrical Attraction - - - - - 31 30.—Revolution of a sun, planet, and satellite - - - - 31 31.—Electrical tree ........ 32 32.—Electrical hail ........ 33 Electric Light illustrated - - - - - 33 33.—Experimental illustration of the egress and access of the electric fluid during the charging and discharging of coated surfaces as rendered evident by means of a discontinuous coating of metallic filings - 33 3(5.—Long zigzag or erratic spark, contrasted with the short straight spark - 35 37.—Of the electrical brush ....... 36 38.—Globe, illuminated panes, and tubes - - - - - 37 39.—Illuminated columns - - - - - - -38 40 —Carreaux etincelantes, (sparkling panes) - - - - 38 41.—Illuminated eggs --------39 Electric Light in vacuo - • - - - 39 42.—Aurora borealis ........ 39 Electrical Ignition experimentally illustrated - - - 40 43.—Ignition of cotton by the electric spark - . - - 40 44.—Inflammation of ether by the electric spark - - - - 40 45.—Ignition of inflammable matter by the electric spark.—Ignition of hydro- gen with oxygen - - - - - - -41 Of mitigating the effects of Electricity - - - 41 Of the proper mode of constructing, and putting up, lightning rods - 42 46.—Experimental illustration - - - - - - 43 Additional means of producing Electricity - - 43 Of the electrophorus.—Of electricity evolved by the friction of caout- chouc, by pressure, by chemical changes, and by the contact of hetero- feneous metals --......43 the electrophorus - - - - - - -43 Evolution of electricity from caoutchouc by friction - - - 44 Of electricity evolved by pressure - - - - 44 48.—Evolution of electricity from caoutchouc by pressure - - - 44 Theoretical Explanation of Electrical Phenomena - - 45 Of the theory of two fluids - - - - - - 45 Additional remarks explanatory of Franklin's hypothesis - 46 Rationale of electric light and ignition - - - 47 49.—Means of Electrifying a Patient with Sparks - . 47 50.—Apparatus for Electrifying a Patient by Shocks - . 48 LECTURES ON A BRIEF HISTORY OF ELECTRICITY. An attractive power is acquired by resins, sulphur, glass, and a variety of other substances, when rubbed; and if the masses, thus excited, be sufficiently large, the phenomena of light, of mechanical concussion, and igni- tion, may result; and even a feeble imitation of thunder and lightning. As it was in amber, in Greek called Electron, that the attractive power, arising from friction, was first observed; the principle to which it was ascribed, was called Elec- tricity; and all substances, in which it could be produced, Electrics. We are informed, that Thales, of Miletus, who flourish- ed six hundred years before Christ, was so much struck with this effect of the friction of amber, as to imagine that it might be endowed with animation. Subsequently, it was ascertained, that the attractive power, which had been observed in amber, when subjected to friction, might be produced, by the same means, in other resinous sub- stances; and, in the tourmaline, or lyncurium, as it was then called, by exposure to heat. No further progress was effected in electrical know- ledge, until the seventeenth century, when after consider- able additions had been made to the catalogue of elec- trics by Gilbert and Boyle, Otho Guericke discovered A 2 that light and sound might result from electric excite- ment. His observations were made by means of a globe of sulphur, cast in a glass vessel which was fractured to extricate the casting. Little was it suspected by the inge- nious operator, that the glass globe, thus broken, would have answered better for the purpose in view, than the globe of sulphur, in the moulding of which it was sacri- ficed. The discovery of the usefulness of glass, as a mean of producing Electricity, appears to have been made by Hawkesbee, who wrote in 1709. To Grey, who followed Hawkesbee, we owe the remark, that the electrical ex- citement of glass, and other electrics, was communicable to other bodies, when insulated, not only by direct con- tact, but by wires or threads of great length; and by this Electrician, in conjunction with another named Wheeler, it was first observed, that this property, of conducting the electric virtue, while belonging to flax or hemp, did not belong to silk; also, that by the class of bodies, in which Electricity can be excited, it cannot be conducted; whilst in those by which it mayT>e conducted, it cannot be ex- cited. Thus were two classes of bodies distinguished; one as electrics, or non-conductors; and the other as non-electrics, or conductors. It was ascertained, however, that a conductor, if sup- ported by a non-conductor, might receive the electric vir- tue from an excited electric. A conductor, so supported, was said to be insulated. Du Faye, soon after, ascertained the important truth, that there are two kinds of electrical excitement. One of these, being observed in glass, was called vitreous; and the other, resinous, because observed in resins. By the communication of either species of excitement, light bo- dies were made to separate from each other; but, the bodies excited by means of resins, were attracted by such as were excited by means of glass; and when these oppo- site excitements were made, in due proportion, in different insulated conductors; on bringing the conductors toge- ther, a neutralization, and of course an apparent annihila- tion, of the electricity in both, was the consequence. The means of collecting the electric fluid, were, soon after, much improved in Germany; where sparks suffi- cient to kill birds, and ignite spirits and other inflammable 3 matter, were produced by the joint influence of several globes simultaneously excited. In the year 1746, the Leyden phial was invented. Cu* neus and Mushenbrceck, attempting to charge, with elec- tricity, the water contained in a phial, a shock was expe- rienced by Cuneus, who happened to touch the conductor with one hand, while grasping the phial with the other. This phenomenon was soon after explained by Frank- lin. He had ascertained, that whenever either kind of electricity is communicated by friction to one body, the other kind will be created in the mass by means of which the friction is effected, provided it be insulated. When a glass is rubbed by the hand, it takes electricity from the hand, and the person to whom it belongs. If standing on a non-conductor, the person will be electri- fied, at the same time that the glass which lie rubs may, by contact, excite another body; but, then, the electricity of the person who rubs the tube,- and that of the body to which he presents the tube, are of opposite kinds; the former being the resinous, the latter the vitreous electri- city, of Du Faye. A stick of resin would cause the op- posite result, producing vitreous electricity in the person rubbing it; and resinous, in a body touching the resin, subsequently to its exposure to friction. These phenomena were thus accounted for by Frank- lin. Some bodies, (glass for instance) by friction, acquire additional power to hold the electric fluid; and hence draw it frOm the conducting body rubbing them, and give up the excess to any adjoining conductor, when the fric- tion ceases. Resins, on the other hand, have their capa- city for the electric fluid lessened, by rubbing; and hence, while subjected to this process, give it out to the rubber, and afterwards draw on any adjoining body, to supply their deficiency. Glass and resin, therefore, produce both kinds of electricity, which are merely the result of an ac- cumulation, or deficiency, in an insulated body, of a fluid which pervades all nature. A conductor, charged in either way, will produce an electrical current, when pre- sented to other bodies in connexion with the earth. In the one case, electricity will flow into the conductor; in the other case, it will flow out of it. Franklin, also, discovered, that when an electrical stream is directed into a phial, situated like that of Cu- 4 neus, there is, at the same time, a stream proceeding from the outside; so that, in proportion as one surface gains, the other loses; and, accordingly, in a charged phial, one surface will be found vitreously, or redun- dantly, excited; the other, resinously, or deficiently; and a light body, after touching either surface, will be re- pelled by it, and attracted by the other. He inferred, that there was only one electric fluid; to different states of which, the names of vitreous, and resi- nous, electricity, had been applied erroneously. The lat- ter he called negative, the former positive, electricity. Franklin, afterwards, identified lightning with electri- city, by drawing this fluid from the clouds, by means of a kite; availing himself of a contrivance, which had pre- viously been appropriated to juvenile recreation, to make a most sublime and useful discovery. ELECTRICITY, EXPERIMENTALLY ILLUSTRATED. The ingenuity of practical electricians, has given rise to a great number of contrivances, which amuse the spec- tator by producing some striking movements, or changes, consequent to electrical excitement. The various appa- ratus thus originated, has been treated too much as a mean merely of affording amusement. There is not a modification of electrical apparatus which is not depen- dent, for its appropriate effect, upon some property of the electric fluid, which it may consequently serve to illus- trate. I shall endeavour to use the various contrivances, above alluded to, in such order, and with such associa- tions, as to make their employment contribute both to the amusement, and instruction of my pupils.* * The student who aims merely at that general knowledge which may be required at his examination for a degree, is not obliged to study all the matter comprised in my text books. So far indeed am I from exacting attention to every topic thus comprised, that my motive for printing many engravings, descriptions, and some abstruse rationales, is to obviate the necessity of occupying much time with them, during my lectures. Yet there can be no doubt that a student, who will, before, or during the 5 ORDER TO BE PURSUED, IN THE EXPERIMENTAL ILLUSTRATION OF ELECTRICITY. Description of Electrical Machines.—Of the ordinary means of producing Electricity.—Communication of Electricity.— Different kinds of Electricity.—Means of accumulating Electricity.—Means of detecting Electricity.—Effects of Electricity.—Additional means of producing Electricity.— Theoretic explanation of Electrical Phenomena.—On the question, whether there be two electric fluids, or one only. —Means of Electrifying Patients; either with sparks, or by shocks. GENERIC DESCRIPTION OF THE ELECTRICAL MACHINE. A description of the electrical machine, should be appli- cable to every apparatus which bears the name. I am unacquainted with any apparatus, designated as an elec- trical machine, which does not consist of an electric, so situated as to be conveniently subjected to a friction cal- culated to produce electric excitement; one, or more col- lectors, attached to a prime conductor properly insulated; and one, or more cushions, for rubbing the electric. The cushions, in the more perfect forms of the machine, are associated with another insulated conductor. Experience has shown, that of all the electrics, glass is the best for the construction of electrical machines; and of all the possible forms, only two are much in use, those of the cylinder, and of the circular plate. In either case, the friction is produced by the rotation of a shaft occupy- ing the axis of the cylinder, or plate, and fastened by screws or cement. The shaft or axis being secured in one or more collars like the mandril of a lathe, is turned by a winch, or by a band and wheels; which are so pro- portioned and arranged, as to quicken the motion. In cylinder machines, it is usual, besides the cushion, to have a silken flap, of which, one border is sewed to the edge of the cushion, so that it may extend from the cush- ion, till the other border approximates the collectors. course, study them attentively, will be much better prepared to under- stand, with accuracy, the general truths which my apparatus is intended to illustrate; and it is but right, that those who prefer this accuracy of knowledge, from taste or ambition to excel, should have every facility af- forded to them in making the effort. I shall endeavour to indicate the relative importance of the matter by the size of the type. Plate machines are sometimes furnished with silk flaps. 1. DESCRIPTION OF AN ELECTRICAL, PLATE, MACHINE; the Plate mounted horizontally, and so as to show both Negative and Positive Electricity. The power of Electrical Plate Machines, has been generally admitted to be greater, than that of machines with cylinders.—The objection to the former has been, the difficulty of insulating the cushions, so as to display the negative electricity.—Excepting the Plate Machine contrived by Van Marum, 1 have read of none in which this difficulty has been surmounted. It is still insisted upon, by respectable electricians, as if it had not been sufficiently removed by his contrivance. I shall now describe a Plate Machine, by which both electricities may be produced, and which I have used successfully for twelve years. The Plate (thirty-five inches in diameter) is supported upon an upright iron bar, about an inch in diameter, covered by a very stout glass cylin- der, four inches and a half in diameter, and sixteen inches in height, open only at the base, through which the bar is introduced, so as to form its axis. The summit of the bar is furnished with a block of wood, turned to fit the cavity, formed at the apex of the cylinder, and cemented therein. The external apex of the cylinder is cemented into a brass cap, which car- ries the plate. The glass cylinder is liable to no strain. It is only pressed where it is interposed between the block of wood within*, and the brass cap without. The remaining portion of the cylinder bears only its own weight, while it effectually insulates the plate from the iron axis. The brass cap is surmounted by a screw and flange—by means of which, a corresponding nut, and disks of mahogany, the plate is fastened. A square table serves as a basis for the whole. The iron axis, passing through the top of the table, is furnished with a wooden wheel of about twenty inches diameter, and terminates below this wheel in a brass step, supported on a cross of wood, which ties the legs of the table diagonally together. The wheel is grooved, and made to revolve by a band, which proceeds from around a vertical wheel, outside of the table. This exter- nal wheel has two handles; by means either of one or both of which it may be turned. It is supported on two strips of wood, which, by appro- priate screws, may be protruded, lengthwise, from cases, which confine them from moving in any other direction. Consequently, the distance between the wheels may be varied at pleasure, and the tension of the band adjusted. Nearly the same mode of insulation and support, which is used for the plate, is used in the case of the conductors.—These consist, severally, of arched tubes of brass, of about an inch and a quarter in diameter, which pass over the plate from one side of it to the other, so as to be at right an- gles to, and at a due distance from, each other. They are terminated by brass balls and caps, which last are cemented on glass cylinders, of the same dimensions, nearly, as that which.supports the plate. The glass cylinders are suspended upon wooden axes, surmounted by plugs of cork, turned accurately to fit the space which they occupy. The cylinders are surrounded and secured below, by wooden rings screwed to the table. In this way, the conductors are effectually insulated, while the principal strain is borne by the wooden axes. Large Electrical Plate Machine. (E. p. 7.) 78 99 % Electrical Cylinder Machine. (E. p. 7.) 50 9999� 79 7 2. ELECTRICAL MACHINE, with a Plate four feet in diameter. The opposite engraving represents a machine, which I have recently constructed so as to be permanently affixed to the canopy over the hearth of my lecture room. See plate at the commencement of this volume. This situation I have found convenient even beyond my expectations, as the machine is always at hand, yet never in the way. In lecturing, with the aid of a machine on the same level with the lecturer, one of two inconveniences is inevitable. Either the machine will occasionally be be- tween him and a portion of the audience, or he must be between a portion of the audience and the machine. Situated like that which I am about to describe, a machine can neither hide the lecturer, nor be hidden by him. With all its power at his command, while kept in motion by an assistant, he has no part of it to reach or to handle besides the knob and sliding rod of the conductor, which is in the most convenient situation. The object of this machine being to obtain a command of much electri- cal power for experiments, in which such power is requisite, it was not deemed necessary to insulate the cushions and the axis, as in the horizon- tal plate machine. The prime conductor is insulated upon the same plan, as those de- scribed in the last article. At C C, are the collectors. R, represents a sliding rod, which may be drawn out to such an extent, as to be brought' in contact with any apparatus placed under it upon the table. 3. ENGRAVING AND DESCRIPTION, OF AN ELECTRICAL, CYLINDER, MACHINE. A, the glass cylinder-^-C, the positive, or prime conductor, supported on a glass pillar—E, the collector with its points so projecting as to be quite near to the cylinder. The negative conductor F, is also upheld by a glass pillar, supporting the rubber or cushion to which the silk flap, G, is at- tached. By means of a set screw, the larger wheel may be made more or less remote from the smaller one, so as to adjust the tension of the band by which motion is communicated to the one, from the other. The former being turned by the winch, causes the smaller one to re- volve, and of course the cylinder, to the axis of which it is affixed. The revolution of the cylinder while the cushion is pressed against it by a suit- able spring, causes the friction which is requisite to excite each portion of the cylinder as it successively passes the cushion. Each of the conduc- tors is furnished with projecting brass knobs, whence to take sparks. OF THE USUAL MEANS OF PRODUCING ELECTRICITY. It has been stated, in the preceding Lecture, that an attractive power is acquired by resins, sulphur, glass, and a variety of other substances, when rubbed:—also, that bodies, susceptible of this species of excitement, are called Electrics—and the principle, on which it is supposed to be dependent, is called Electricity. 8 A, represents a glass tube. B,.a similar tube coated with shell lac, or sealing wax. C, an iron rod, furnished at one end with a wooden handle, while throughout the greater part of its length, it forms the axis of a cylinder of sulphur. Either of the instruments thus constituted, being rubbed, either with a silk handkerchief, a cat skin, or a leather coated with amalgam, will become sufficiently excited to attract leaf metal, and produce other indications of electricity. The amalgam and leather, can only be used advantageously with the glass. 4. EXPERIMENTAL ILLUSTRATIONS. Friction of amber, glass, resin, sulphur. Large glass tubes rubbed—also, cylinders of sulphur and of resin. Thin metallic leaves attracted, at a considerable distance, either by the glass, the sulphur, or the resin. Electrical machines put into operation. OF THE COMMUNICATION OF ELECTRICITY. The electric virtue cannot pass from one part of an electric which is excited, to another, without extraneous aid; nor can it pass off, from one electric, through any other.—Hence these substances are called non-conduc- tors. Through metals, on the other hand, it escapes in- stantaneously. It passes with ease through flax or hemp, but not through silk. Water it pervades with great faci- lity—or any thing which contains moisture. Substances, which are thus capable of transmitting electricity, are called conductors; and are divided into perfect, and imperfect conductors. The metals are the 9 only perfect conductors. All other conductors are imper- fect; and, at the head of this class, is charcoal, as being the best conductor of electricity, next to metals. experimental proofs, that electricity does not pass from one part of an electric to. another, through, or by means of, an electric. 5. an experimental illustration. One part of a cylinder of sulphur, or of glass, being ex- cited by friction, so as to attract light bodies; another part, not being rubbed, is not found to attract them. 6. PEALE'S EXPERIMENT. Among the multitude of electrical contrivances already alluded to, that which we owe, as I believe, to Mr. Franklin Peale, deserves more than ordinary praise for its simplicity of construction, and beauty of effect. One modification of Peale's apparatus is represented by the following engraving, which I shall proceed to explain. A bell glass is balanced upon a pivot reaching internally to the apex, between wires supported on glass pillars. One wire A, communicating with the positive, the other, B, with the negative pole of the machine. Under these circumstances, if the machine be put into operation, the por- tion of the glass next to the wire A becomes positively excited, that near B, negatively excited. Consequently, agreeably to the general law that bodies similarly electrified separate, those dissimilarly electrified approach; each excited portion of the glass will move away from the wire similarly excited, and will seek that which is differently excited. Thus the excite- ments changing the situations of the excited parts, and their exchange of B 10 situation reversing their excitements, a rapid movement must ensue, in the only mode in which it can take place freely, I mean that of a rotation on the pivot. The bell is ornamented by strips of gilt paper, which renders the mo- tion more sensible to the eye; but no coating is requisite to the appro- priate effect—a bare bell glass is sufficient. If the metallic band C be made to encompass the bell glass, it will be found incapable of receiving any motion from the electrical excitement. In fact, the electric fluid will be seen passing into it on one side, and pass- ing out of it simultaneously on the other side; proving that it cannot, under these circumstances, retain any excitement, in consequence of the conducting power of the metallic band. Mr. Peale's experiment was performed by means of a globular glass vessel with a short neck, or perforation for the admission of the pivot wire. The pupil will perceive that I have availed myself of this apparatus, to show that the electrical excitement communicated to one part of a non- conductor, does not extend itself to others; and that consequently in dif- ferent parts of the same non-conducting mass, opposite kinds of electrical excitement may be produced. It is owing to this property, that the glass bell is put into motion. The electric fluid, being unable to pass along the glass, in its efforts to seek an equilibrium, it moves the glass along with it in consequence of an attraction arising between each wire, and that part of the glass which has a different excitement. That the phenomenon owes its existence to the non-conducting power of the glass, is shown by encircling it with a metallic band, through which the fluid passes from one side of the glass to the other with perfect ease. Under these circumstances, that diversity of excitement, which would cause the rotatory motion, cannot arise. 7. MODIFICATION OF PEALE'S EXPERIMENT. The following figure shows a modification of Peale's apparatus, by which I have contrived to put three globes in motion. 11 8. ADDITIONAL ILLUSTRATION. The principle explained by the preceding experiment receives another amusing illustration by means of an experiment, for the explanation of which this engraving is intended. A glass ball is supported on a glass plate. On the plate, strips of tin foil are so pasted, as to form a broad circle or border near the margin of the plate, and four radii to that circle. There is likewise a flat brass ring supported, and of course in- sulated, by glass pillars, so as to have its inner edge immediately over that of the exterior edge of the foil. The brass ring being in communication with the prime conductor of the machine in operation, and the tin foil in communication with the cushions, the ring and foil will be oppositely electrified. The ball, being attracted by the ring, becomes posi- tively electrified in the part which comes in contact with it. The part thus elec- trified will then be attracted by the foil; and communicating its charge, return to the ring to undergo another change. Different parts in succession undergo these electrical changes, and the consequent movements; which are of course compli- cated and amusing. 9. EXPERIMENTAL PROOFS, THAT METALS, CHARCOAL, MOISTURE, FLAX, OR HEMP, ARE CONDUCTORS OF ELECTRICITY---AND THAT SULPHUR, RESINS, GLASS, SILK, AND WOOL, ARE NON-CONDUCTORS. The Electrical Machine, being in operation, so as to emit sparks, or to act upon pith balls, or other light bo- dies—those electrical effects cease, when the conductdr, which is the immediate cause of them, is touched with a rod of metal, or b>y a piece of charcoal, communicating with the earth—and they are enfeebled, when one end of 12 a hempen or flaxen string is attached to the conductor, while the other end is held in the hand, or lies upon the floor. The conductor being excited, as above described, the phenomena do not cease, in consequence of the contact of a glass rod, or of cylinders of sulphur or resin; nor are they diminished, by an attachment of woollen or silken strings, as in the case of those of flax or hemp. The glass rod, or the woollen or silken strings, being soaked in water, the electricity is carried off by them from the conductor. Electricity escapes from the conductor, with ease, through a tube filled with water. OF THE DIFFERENT KINDS OF ELECTRICITY. It may be learned, from the brief account of the rise and progress of Electricity, (page 2) that the electrical excitement which may be produced in glass, by friction, differs from that which may be produced, by the same means, in resin, or sulphur: that light masses, as paper, or pith balls, separate from each other, when either ex- citement has been imparted to both: but if one body re- ceives the resinous, the other the vitreous excitement, an attraction between them will ensue. Both excitements, in due proportion, neutralize each other. Also, whenever either excitement is produced, in one body, the other will arise in some other, if both bodies be supported by non- conductors, so as to prevent the escape of electricity, as soon as generated. Hence if a person, standing on a glass stool, rub a tube of the same material, he will be found resinously electrified; while any body, to which the glass may be presented, will be vitreously electrified. A stick of resin, being substituted for the glass, and rubbed in like manner, and under the same circumstances, the same phenomena will appear, in a different order. The person rubbing the resin, will be vitreously excited; while the excitement of the body, to which it is presented, will be resinous. In like manner, when the cylinder of the electrical ma- chine is put into motion, the insulated cushion which rubs it, acquires the resinous excitement; while the prime con- ductor becomes excited vitreously. If a globe of sulphur, 13 or resin, were substituted, the cushion would receive the vitreous excitement; while the conductor would be ex- cited resinously. 10. DESCRIPTION OF BENNET'S GOLD LEAF ELECTROMETER. A glass cylinder, supported by a metallic pedestal, is surmounted by a metallic cano- py ; from the centre of which, two tapering strips of gold leaf are suspended. Strips of tin foil, T T, are pasted on the glass, so as to terminate at the upper ends a little above the level of the lower ends of the gold leaves, and so as to be in contact below, with the pedestal. This should be uninsulated. The gold leaves are more energetically attracted in consequence of the proximity of the tin foil. 11. EXPERIMENTAL ILLUSTRATIONS. The leaves of the Electrometer diverge, on the ap- proach either of excited sulphur or glass; but when both are approximated to it, at once, the leaves will display no divergency. Electrical Machine produced—each conductor being furnished with a Quadrant Electrometer. As the cylin- der is turned, the pith ball of each Electrometer rises. As often as a spark is taken from either conductor, the pith ball of the Electrometer on it, falls; and when a me- tallic wire is made to touch both conductors, simulta- neously, neither of the pith balls indicates any excite- ment. OF ELECTRIC POLES.—OF ELECTRIC CIRCUITS. There is a resemblance which will hereafter be recurred to between the reciprocal action of magnets, and that of electrics, of which, the extremities are in opposite states. Under such circumstances, the poles similarly electrified, or similarly magnetised, appear to repel each other, while those in dissimilar states, appear to exercise a reciprocal attraction. The extremities of the magnets, from their exercising a reaction with the terrestrial poles, analogous to that 14 which they exercise reciprocally, were called poles; that which is attracted by the north pole of the earth being designated as the north pole, the other as the south pole. From the analogy, the extremities of excited electrics, and galvanic and voltaic instruments having properties resembling those of excited electrics, received the same appellation. Hence electricians speak of the positive and the negative poles, of the electric machine, of the galvanic battery, or of a voltaic series, whether in the form of the trough, or of the pile. As a general definition, poles may be alleged to be those parts of an electric, galvanic, or voltaic circuit, at which ignition, light, chemical decomposition, or sensa- tion, are perceived. When the conductors of a machine, in operation, com- municate by a wire or rod, or other competent conduct- ing body or bodies, an electric circuit is said to be formed. The electric fluid flowing into the cushion from the nega- tive conductor supporting it, is, by the electric, carried to the positive conductor, whence, by means of the conduct- ing communication, it returns to the negative conductor. Agreeably to the hypothesis of two fluids, there is in such case a double circuit. Two fluids separated from each other by the friction, move in opposite directions, and meeting and combining in the conductors as soon as se- parated, the equilibrium is not sensibly altered. In making or breaking such a circuit, sparks will appear at the time and place, when and where the interruption is such as to allow them to occur. In that case the poles are at the points through which the sparks pass. The poles of an electric machine, and the conductors, are often mentioned as if they were identical. In fact, the poles are usually at some points in the surfaces of those conductors. They vary, however, at the pleasure of the operator; since they always exist at those parts of the conductors (or of any conducting body or bodies touching one or both) which are nearest to each other, or at which sparks pass. It should be understood that any conductor, especially any perfect conductor, assumes the same electric state as the pole, with which it may be in connexion; and that a contact between either pole, and one extremity of a rod, or wire, transfers the polar influence to the other end of 15 that rod or wire. The pole is properly, that point at which the excitement is most active, and experience shows this state to exist always, either at the most pro- minent part of the electrified mass, or that nearest to any prominent part of the other pole. In operating with an electric machine, of which the rubber is uninsulated, the earth usually forms a part of the circuit, and any conductor, the human body for in- stance, which, while it has a conducting communication with the earth, happens to be nearest to the positive pole, acts as the negative pole, when the machine is in opera- tion, and there is sufficient proximity. This is indicated by the passage of sparks. I have dwelt upon this subject more particularly, as the acceptation of the word pole, among men of science, has latterly, by its practical and theoretical associations, be- come of the highest importance. Students who wish further information on this sub- ject, are referred to an article in the appendix, entitled, "Remarks on the Error of supposing a Communication with the Earth, necessary to the Efficacy of Electrical Ma- chines." MEANS OF ACCUMULATING ELECTRICITY. In the case of the insulated conductors of an electrical machine, oppositely excited by the revolution of a glass surface which successively rubs the cushions supported by one of the conductors, and passes under metallic points projecting from the other; it has been shown that it is only necessary to make a communication between them, by a perfect conductor, in order to destroy their respective excitements. It follows that the surcharge in the one, must have been just equivalent to the deficiency in the other; and that of course the whole quantity of electricity in the conductors is the same, whether they be in a state of excitement or of quiescence. It has also been shown, that the electric fluid does not pass through electrics, or from one part of an electric to another. I shall now proceed to demonstrate, that if an electric, sufficiently thin and strong, (as a pane of glass for in- stance) be charged on either side with either kind of elec- 16 tricity, the other side of the pane will acquire, propor- tionably, a charge of the opposite nature. 12. EXPERIMENTAL ILLUSTRATIONS. A dry glass pane being held in one hand by its insulating handle, sparks are taken from the excited conductor of an electrical machine, with the knuckle of the other hand. The glass pane, being interposed between the knuckle and the conductor, at first does not appear to intercept the sparks; yet, as they gradually diminish, and finally cease, they are obviously intercepted by the pane, sooner or later. The pane being supported by the handle, on touching the sur- faces in the part which has been exposed to the sparks, with one hand, while the part opposite on the other side of the pane is touched by the other hand, an electrical discharge takes place, a shock is experienced, and the electrical ex- citement disappears. It follows, that the sparks which had appa- rently passed through the pane, had actually been arrested by the surface nearest to the con- ductor, and had appeared to reach the hand; because, for every spark received on one side, an equivalent portion of the electric fluid is ex- pelled in the same form from the other side. 13.- COATED PANE. A pane of glass is coated on both sides with tin foil, excepting a space of about two inches from the edge all round. The two coatings are made severally to communicate, for a short time, with the two insulated conduc- tors of an electrical machine, while in operation, the coatings being other- wise insulated. The pane being then suspended, and the different coatings 17 severally allowed to communicate through a metallic arc, a discharge en- sues, more or less powerful, according to the power df the machine, the extent of the coated surface, and the dryness of the air. 14. OF THE LEYDEN JAR. In the History of Electricity, (page 3) some account has been given of this cele- brated invention. The adjoining cut is a representation of it in an approved form. There is no essential difference between a coated phial, and a coated pane. The existence, or the absence of curvature in the interposed stratum of glass, does not sensibly affect the result, neither in theory, nor in practice, except- ing as respects conveniency. The form of the jar is more favourable to the retention of a charge, as it does not allow such free intercourse, between the inner surface and the air. The coating, it will be observed, is re- presented as extending both on the inside and on the outside, till within a distance from the brim equal to about one-fourth of the whole height of the jar. The jar is closed by a broad wooden stopple, through the centre of which passes a metallic rod, terminated above by a knob, and below by a spiral of wire, which establishes a sufficient contact with the inner coating. The most convenient mode of charging such a jar, is to grasp it in the hand, and present it to the knob of the prime conductor, while the cush- ions are uninsulated, or in communication with the outer coating by means of a chain or wire. 15. OF THE COMMON DISCHARGER. c 18 This name is given to an instrument, of which the preceding figure is a representation, and which is employed in completing the circuit between the charged surfaces; thus enabling the excess in one, to be discharged into the other. The rods, R, R, are joined by a hinge; so that, by means of the glass handles to which they are severally affixed, the terminating knobs may be made to come into mutual contact, or to be remote from each other, as in the figure. A charge is imparted, equally well, by the contact, or com- munication, of either coating, with either conductor. The charging of a coated pane, or jar, may be effected, provided either of the surfaces are in communication with either conductor, the other surface communicating with the other conductor; one or both of the conductors being insulated. In whatever way a charge may be induced, it will be found that the one surface loses as much as the other gains; since a conducting communication is always sufficient to bring them both back to a state of neutrality. Hence as the sum of the quantities on both sides of the pane, is always the same, charging the pane, does not derange the electrical equilibrium of the surrounding me- dium. The charge must vary in its strength, according to the power of the machine, the dryness of the air, and the thickness of the glass; since the self-repellent power of > the electric particles, and their attraction for the negative surface of the glass, must be inversely as the squares of the distances at which they operate. On this account as a plate of mica may, with less thickness, possess greater strength than a glass pane, it will, in proportion to the respective areas, receive a much higher charge. A certain degree of strength, is neces- sary to enable the glass to resist the intense attraction between the surcharge of electricity on the positive side, and the surface of the glass on the negative side. In ob- taining this strength in the glass, we increase the dis- tance between the surfaces, and of course diminish the efficacy of the self-repellant, and attractive powers, on which the charge depends. 16. EXPERIMENTAL ILLUSTRATIONS. That the charges may be imparted through either coat- ing, by either conductor, shown, by duly charging, and discharging, coated panes **."** iars 19 17. EXPERIMENTAL PROOFS, THAT THE DIFFERENT SURFACES OF A CHARGED ELECTRIC, ARE OPPOSITELY ELECTRIFIED. If from the conductor of an electrical machine in operation, a Leyden jar be suspended by a metallic hook, connected with one of its coatings, it receives no charge, until the other coating is approximated by a conduct- ing substance, which communi- cates directly, or indirectly, with the other conductor of the ma- chine. If one or more bodies, as, for instance, little metallic balls, qualified to act as bell clap- pers, be suspended at a suitable distance between bells severally communicating with the coatings of a charged pane or jar, the balls will play between the bells demon- strating them to be oppositely electrified by their com- munication with the different surfaces. 18. CHIME OF BELLS. 20 The little metallic balls, b, i»,and the bell situated between them, being suspended by silk, which is a non-conductor, cannot receive the electrical excitement com- municated to the inner coating of the jar. But the two outer bells, being suspended by metallic chains from a metallic rod communicating with the inner coating, will partake of Jhe excitement in this coating. Consequently the balls remaining neu- tral, while the outer bells are excited, are attracted by these, and on coming in con- tact with them receive a quantity of the electric fluid adequate to bring them to the same degree of excitement. Hence in the next place they separate from these bells, and are attracted by the central bell, which, by means of a chain connecting it with the external surface of the jar, is brought into the same electrical state as this coating, and must of course be in a state opposite to that of the other surface. The balls, by contact with the central bell, lose as much electricity as will bring them to the same state as this bell, and are then separated from this bell, and are attracted by the others, are again separated, and are again attracted, until by repe- tition, they transfer the surcharge on one surface to the other, and thus restore the equilibrium. Gravitation operating upon the balls as upon the pendulum of a clock, evidently conspires to sustain their vibrations. The length of time, that the bells may be kept ringing by the vibration of the balls, when the air is dry, may excite surprise at first; but it should be recollected that the balls can only carry off at each stroke, a portion of the electric fluid; which is, to the whole quantity in the coating, as the superficies of the ball is to the sur- face of the coating, or less, probably, than as one to ten thousand. Metallic Coatings employed, as in the preceding experi- ments, are of use in conveying the charge—but it does not reside in them. The effect of the tin foil, is, simply, to cause the speedy and equal distribution of the electricity over the surface of the glass, which, not being an electric, cannot by itself convey the excitement from one part of its surface to another. Hence a pane without coatings, can only be partially charged or discharged at one contact. 19. PANE WITH MOVEABLE COATINGS. T T represents metallic sheets, which are used as coatings to a pane, also represented in the figure. One of the sheets is insulated by being supported upon a stand with a glass leg; the other by being held by a glass handle. 21 EXPERIMENTAL ILLUSTRATION. A glass pane, P, held by means of an insulating handle of the same ma- terials, is made to touch the knob of an excited conductor of the electrical machine, on one side; while another metallic knob, communicating with the other conductor of the machine, is made to touch the pane on the other side, in the part opposite to the first mentioned knob. By varying the situation of the knobs, the pane is charged, wherever its surfaces have been sufficiently in the vicinity of the knobs. While thus prepared, it is supported by its handle, and one hand of the operator approximated to one side, while the other hand approximates the other. It can only be gra- dually discharged, as it was charged; the knuckles being made to assume, successively, the various positions relatively to the pane, previously occu- pied by the knobs. But, the pane being again charged by the knobs, with the aid of the coatings, T, T, properly applied; the surfaces are tho- roughly and instantaneously discharged by contact of the hands, or other competent conductor, with those coatings. The coatings being applied to the pane, whilst charging, and then removed, the discharge can only be effected gradually. Any other conducting substance which will accommodate itself to the surface of the glass, may be substituted for tin foil. But metals are pre- ferable, as they are pre-eminently the best conductors. 20. Glass vessel so situated as that water is made to perform the same office as metallic coatings in the Leyden Phial; illustrating the original experiment of Cuneus and Mushenbroeck. A glass vessel, containing a quan- tity of water, of which the surface should be about two inches below the brim, and moistened to the same height on the outside, may, as in the celebrated experiment of Cuneus and Mushenbroeck, be charged and dis- charged, by the same means as the pane or phial coated with tin foil, though less advantageously. Gold, silver, or copper leaf, me- tallic filings, or mercury, may be substituted for the coatings of a Leyden jar. When metallic filings are glued to the surfaces of a pane or jar, within the space usually al- lotted to the tin foil coatings, the discontinuity of the conducting sur- faces, causes the passage of the elec- tricity from one portion to another, to be indicated by splendid corrusca- tions, which will hereafter be fully illustrated. 21. EXPERIMENTAL DEMONSTRATION THAT THE CHARGE OF A LEYDEN JAR, DOES NOT RESIDE IN THE COAT- INGS. That the charge does not reside in the coatings, may be proved by re- moving them, touching them with the hand while separated from the glass; 22 and afterwards replacing them, and simultaneously touching them. A shock will be received, in the same way as if they had not been removed. Instead of tin foil coatings, a metallic case is made, just large enough to receive a tumbler with ease, and reaching about two-thirds of its height. A hollow cylin- der of the same material, is made so as to fill the cavity of the tumbler, to the same height as the case reaches on the outside; and yet so loose, as to be removed without difficulty. The tumbler being charged in the usual way, the cylinder may in the first place be lifted out of the tumbler by means of a glass rod, and the tumbler in the next place grasped at the brim and lifted out of the case without destroying the charge. This is rendered evident, by re- instating the tumbler in its case, and the cylinder in the tumbler; and by means of the discharger making a conducting com- munication between the case and the ball of the wire communicating with the cylin- der. An electrical spark will then pass with the usual noise. Or if the circuit be established by touching the knob with one hand, and the case with the other, a shock will be experienced. OF ELECTRICAL BATTERIES. A series of coated jars, being placed side by side in a box, and all the inner coatings being made to communi- cate with each other, and with a ball of metal, by means of metallic rods; and all the outer coatings being made to communicate with each other, and with another me- tallic ball, by strips of tin foil; the jars, thus associated, are called an Electrical Battery. Charging and discharging an electrical battery, how- ever extensive, is just as simple, and is performed in pre- cisely the same way, as in the case of a single jar. To charge a single jar, or a battery, the different coatings must be made to communicate, severally, with the differ- ent conductors of an electrical machine, either directly, or indirectly, through the floor of the apartment, or other conducting medium.* To effect a discharge, either one, or several conduc- tors, must be made to form a circuit from one coating to the other, either unbroken: or, if interrupted, the inter- * See Appendix, for remarks on the error of supposing that a communication with the earth is necessary, &c. &c- 23 val, or the sum of the intervals, must not exceed a cer- tain distance, called the striking distance, and which va- ries with the extent and intensity of the electrical ma- chine. Charging a battery, will take more or less time, ac- cording to the number of jars to be supplied, and the quantity of the electric fluid, generated by the machine. But the discharge appears as quick from a great num- ber, as from one; notwithstanding the numerous ramifi- cations, through which the electricity has to pass. 22. OF AN ELECTRICAL BATTERY OF 32 JARS, EACH 13 INCHES IN HEIGHT, AND 5 INCHES IN DIAMETER. My electrical battery is represented in the opposite engraving. It is situated permanently on the external edge of the canopy over the hearth of my lecture room, in the vicinity of my large electrical machine. With the positive conductor of this, it is of course easily made to communicate by a metallic rod. From the outer coatings a wire is extended to one of the iron columns of my lecture room, along which it afterwards descends to my table, and when the battery is in use,to a sheet of metal, on which, the battery discharger is placed. (22.) 23. DESCRIPTION OF HENLEY'S UNIVERSAL DISCHARGER. This instrument has been employed to facilitate the exposure of bodies to a dis- charge from a Leyden jar or battery. It may be understood from inspection. Two rods are supported upon glass pil- lars, to which they are secured by universal joints, having not only liberty to move on a pivot in almost any direction, but also to be slid through a spring socket so as to lengthen or shorten the portion of the rod between the socket and the point. The ends of the wires are pointed, but the points are fitted to brass balls which may be screwed on or off. Between the columns is a little stand, which may be altered in height by means of a set screw. Upon this stand, an object to be made the medium of a discharge may be placed; the ends of the wires being in due contact with it. To one of the eyes at the other ends of the rods, a wire or chains, communicating with a coating of the battery, may be aflixed. By means of the common discharger (15) a commu- nication being then made between the other rod, and the other coating of the bat- tery, the circuit is completed, and the whole charge, of the battery, passes through the body upon the stand. 24 In some cases where pressure is required, the stand represented at E, is employed. Thus some gold leaf being compressed between two very small panes of glass, kept together by the screws with which this last mentioned stand is furnished, may be deflagrated and incorporated with the glass. 24. BATTERY DISCHARGER FOR DEFLAGRATING WIRES. This apparatus is employed by me in lieu of Henley's universal discharger above described, being better adapted to my apparatus, and mode of operating. Two brass plates are secured to the pedestal, by a screw bolt, N, which passes through a hole made in each, near one extremity: the plates are thus allowed a circular motion about the bolt so as to be set in one straight line, or in any angle with each other. On one of the plates near the extremity not secured by the bolt, a brass socket is soldered, into which a glass column is cemented, surmounted by a forceps. At the corresponding end of the other plate, there is a brass rod, R, perpendicular to the plate, and parallel to the glass column. This rod, is also furnished with forceps. Between these forceps, and those at F, supported, and insulated by the glass co- lumn, C, a wire is stretched, which may be of various lengths, according to the angle which the plates, S, S, make with, each other. The pedestal should be me- tallic, or have a metallic plate at bottom, in communication with the external coat- ing of the battery. This being accomplished, it is only necessary to charge the battery, without subsequently breaking the communication between the inner coat- ings of the jars, and the prime conductor, by which the charge is conveyed. In that case touching the conductor, is equivalent to a contact with the inner coatings of the jars, so far as electrical results are concerned. Hence, by causing one of the knobs of the discharger, D, with glass handles, to be in contact with the insu- lated forceps, F, and then approximating the other knob to the prime conductor B the charge of the battery will pass through the wire, W, as it cannot descend by the glass column, nor reach the operator through the glass handles. 25 OF ELECTRICAL EXCITEMENT BY INDUCTION. The simplest case of this kind, is that of the Leyden phial, or coated pane, already illustrated; where one sur- face, being in contact with an excited conductor, a ten- dency is induced in the electricity, on the other side of the electric, to leave it. This, probably, arises from that self-repellent power, between the particles of the electri- cal fluid, with which Franklin supposed them to be en- dowed. 25. APPARATUS FOR THE ILLUSTRATION OF ELECTRICAL INDUC- TION. If the outer and inner coatings, of two or three insu- lated jars, be made to communicate; and the coatings of each extremity of the series, be brought into communica- tion with the conductors of a machine in operation, as usual when one jar is to be charged; it will be found that a charge is received by all, and in discharging them, a spark may be perceived to pass between each jar, if a small interval be left. The effect of the discharge, is less than that which would be produced by means of one jar. In this case, the surfaces are said to be charged by induc- tion. The number of jars which can be thus affected, is greater, or less, according to the intensity of the electri- city evolved by the machine, and the aggregate thickness of glass interposed. 26. A NEW APPARATUS FOR THE ILLUSTRATION OF ELECTRICAL INDUCTION. As the prevailing theories of electricity cannot be understood without a correct idea of electrical induction, for the purpose of rendering it more in- telligible, I have constructed the apparatus described in the following arti- D 26 cle. The surfaces oppositely charged, being in the case of panes exactly alike, renders their commutable relation more easy to understand; and the process, as it proceeds in them, having a greater resemblance to that ascribed to voltaic series, may hereafter be more advantageously cited as a mean of illustration. A series of five panes coated on both sides with tin foil, excepting about two inches from the edges, are situated in a frame at the distance of about two inches apart. A metallic communication is established between the inner coating of the first pane in the row, and that of the second pane im- mediately opposite, by means of a spiral spring of wire, which, by its pres- sure, keeps its place, and produces a close contact with the tin foil. A similar spring is interposed between each pair of coatings. Also the ex- ternal coating of the first, and that of the last pane in the series, com- municate severally by wires with metallic knobs, A, B, supported upon, and of course insulated by glass pillars. That is, the first pane commu- nicates with the knob at A, the last with the knob at B. This apparatus, like a Leyden jar, may be charged in either of three modes. That in "which the positive pole alone is insulated from the earth, that in which only the negative pole is insulated; and that in which both poles are insulated. When the operation is performed with the positive pole insulated, the negative pole communicating with the earthy the surcharge induced in the coated surface of the first pane, expels from the inner coated surface of that pane a portion of electricity, which is of course driven through the spiral into the nearest coated surface of the pane next in order. The surcharge induced thus in the nearer surface of the second pane, causes the other surface of this pane to give up electricity to the nearer surface of the third pane; so that, by a repetition of the process, every pane will be charged, if the electricity be sufficiently intense. If, under these circumstances, cfne of the knobs of the insulated dis- charger be made to touch one of the insulated balls, while an approxima- tion of the other knob to the other ball is effected; a spark will pass, arising from a discharge from the surface of the first pane, to that of the last, and at the same instant the equilibrium in all the surfaces will be re- stored. During the entrance of the charge, the apparatus only receives an ac- cess of the fluid on the external coated surface of the first pane, and loses 27 a portion from that of the last pane. In the other surfaces the quantity is not altered, since whatever one loses, the other gains, and the quantities in the surfaces of each pane are equalized with the restoration of the equili- brium of the two external coated surfaces. When the operation is performed with the negative pole in a state of in- sulation, it will be the converse of that above described. Electricity being abstracted from the external surface of the fifth pane, instead of being ac- cumulated upon that of the first pane, the internal surface of the fifth pane becomes positively excited at the expense of the nearest surface of the fourth pane, which of course becomes negative on the surface thus robbed, and positive on the other side at the expense of the coated surface of the third pane. Thus by a successive inductive influence, transmitted from pane to pane, every other surface is negatively charged, causing those which alternate with them, to be charged in the opposite way. When the knobs, A, and B, are acted upon by a machine with both poles insulated, the two processes above described co-operate simulta- neously: since while electricity is abstracted from the external surface in direct communication with B, on the right, it is accumulated upon the external surface communicating with A, on the left; so that, by the induc- tive process, each pane becomes charged. MEANS OF DETECTING OR MEASURING ELECTRICITY. It has been seen, that the property which light bodies have of separating from, or approaching to, each other, when electrified, has been of use in showing the nature and extent of electrical excitement. A ball of pith, supported by a radius, suspended from a pivot, so as to be capable of describing an arc of ninety degrees, over a corresponding curved scale, constitutes Henley's Quadrant Electrometer, employed in the experi- mental illustrations, 11. Bennet's Electrometer has been described; in which, metallic leaves are suspended, within a glass cylinder, to a metallic cap. Slips of tin foil being pasted on the glass, opposite, and parallel to, the gold leaves. This last mentioned instrument, is sometimes, more properly, called an electroscope; as it is better calculated to discover electricity, than to measure it. The efficacy of the gold leaf electroscope, is much in- creased by the addition of two metallic disks, one sol- dered to the cap, the other attached to the foot, by a hinge; so as that it may be placed parallel, and as near to the first mentioned disk as it can be, without touching. In this case, the capacity for electricity, of the disk, at- tached to the cap, is found to be increased, by induction; so that it will receive a surcharge. When the disks are separated, the excess of electricity received, while they 28 were near each other, is indicated by the divergence of the leaves. The instrument thus constituted, is called the con- densing electrometer, of which, an engraving and de- scription is annexed. 27. DESCRIPTION OF THE CONDENSING ELECTROMETER. The condensing electrometer, of which the annexed figure is a re- presentation, differs from the ordi- nary instrument, in being furnished with two metallic disks, one attach- ed to the canopy, C, the other up- held by a wire. The wire termi- nates in a hinge at A, by which the disk which it supports may be made to approach, or retire from the other disk. The metallic hinge commu- nicates by a strip of tin foil, with - other strips of the same material, which are pasted on the glass, as already described in the case of the gold leaf electrometer (10). In order to put this instrument into operation, the disks must be quite parallel, and as near each other as possible without contact; then, on touching the cap with an electrified mass containing a charge of elec- tricity, otherwise too low to affect the leaves, and afterward removing the disk, D, to the distance of two or three inches, the leaves diverge. A di- vergence of the leaves of the condensing electrometer may be produced by supporting a zinc disk of about six inches in diameter in the hand or other- wise, so as to have a communication, directly or indirectly, with the pedestal of the electrometer, and placing on it, from ten to twenty times, a disk of copper of the same size, held by a glass handle, and at each removal bringing the copper disk in contact with the cap of the electrometer. By these means a charge is imparted to the cap, which, when the outer disk is removed, is evinced by the divergency of the leaves. For our knowledge of the last mentioned method of producing electricity, by the contact of heterogeneous metals, we are indebted, I believe, to the celebrated Volta, I have constructed an electroscope with a single leaf, to which a brass ball may be approximated by a micrometer screw. This is more sensi- tive, than any electrometer which I have seen on the usual plan. When furnished with a cap of zinc, if a plate of copper be placed on the cap, and then lifted, the leaf will strike the ball. This instrument acts both as an electroscope, and as an electrometer—as it detects and measures the mi- nutest degree of excitement. 23. DESCRIPTION OF THE SINGLE LEAF ELECTROMETER. By which the Electricity, excited by touch of heterogeneous metals, is rendered obvious, after a single contact. A single gold leaf is suspended from a disk of zinc six inches in diameter, which constitutes the cap of the instrument. Opposite to this single leaf, a ball is supported which may be made to approach the leaf, or recede from it, by means of a 29 screw. Of the same size as the disk which forms the cap there is a copper disk with a glass handle, accompanying the instrument.* The electricity produced by the contact of cop- per and zinc, is rendered sensible in the following manner. Place the disk of copper, on the disk of zinc, (which forms the cap of the Electrome- ter)—take the micrometer screw in one hand, touch the copper disk with the other, and then lift this disk from the zinc. Usually, as soon as the separation is effected, the gold leaf will strike the ball, if the one be not more than the twen- tieth of an inch apart from the other. Ten con- tacts of the same disks, of copper and zinc, will be found necessary to produce a sensible di- vergency in the leaves of the Condensing Elec- trometer. That the phenomenon arises from the dissimilarity of the metals, is easily shown, by repeating the experiment with a zinc disk, in lieu of a disk of copper. The separation of the homogeneous disks, will not be found to produce any contact, between the leaf and ball. I believe this to be the only mode in which the electrical excitement, produced by the contact of heterogeneous metals, can be made evident without the aid of a condenser. It is probable, that the sensibility of this instrument is dependent on that pro- perty of electricity, which causes any surcharge of it, which may be created in a conducting surface, to seek an exit at the most projecting termination, or point, connected with the surface. This disposition is no doubt rendered greater, by the proximity of the ball, which increases the capacity of the gold leaf to receive the surcharge, in the same manner, as the uninsulated disk of a condenser, 27, influ- ences the electrical capacity of the insulated disk, in its neighbourhood. It must not be expected, that the phenomenon above described, can be pro- duced in weather unfavourable to electricity. Under favourable circumstances, I have produced it, by means of a smaller electrometer, of which the disks are only two and a half inches in diameter.t The construction, as respects the leaf, and the ball, regulated by the microme- ter screw, remaining the same—the cap of a condensing electrometer, and its disks, may be substituted for the zinc disk. 29. DESCRIPTION OF HENLEY'S QUADRANT ELECTROMETER. Henley's Electrometer consists of a little wooden column, supporting a semicircle of ivory, or of wood covered with white paper; graduated near the peri- phery, into 180 degrees. At the centre of the semi- circle, there is a pin, from which a moveable radius, terminated by a pith ball, is suspended. This radius is sufficiently long to allow the ball to reach to the base of the column, against which when left to itself it rests. But when the ball and column are electrified, the ball moves off from the column together with the radius to which it is affixed. But the radius being se- cured to the pivot at its upper end, the ball must de- scribe a greater or less portion of a circle which is at the same time indicated and measured by the gradua- tion. * For the experiment with this electrometer, a metallic handle would answer. Its being of glass, enabled me to compare the indication, thus obtained by my in- strument, with that obtained by a condenser. t I think I have seen an effect from a disk only an inch in diameter, or from a zinc disk, having a handle with a copper socket. 30 29£. OF COULOMB'S ELECTROMETER. The electrometer of Coulomb is suitable rather for the investigation, than for the illustration of electrical phenomena. Yet as it may be pro- per to convey an idea of the principle of this instrument, I shall quote from the Treatise on Heat and Electricity, of the distinguished Dr. Thom- son, of Glasgow-, a description, accompanied by an engraving of the elec- trometer in question, in the most simple form. Alluding to the gold leaf electrometer, (10) or that in which straws are used in place of gold leaves, Dr. Thomson observes:— " In these and many other common electrometers which I think it needless to describe, the instrument cannot be considered as a true measurer of the quantity of electricity, because as the two straws or the two slips of gold leaf separate farther and farther from each other, it is evident that gravitation will act more and more powerfully to bring them back again to their naturally vertical position. Hence the repulsive force of the straws, or leaf, is not proportional to the distance to which they separate from each other. These instruments cannot of course be employed to measure the energy of electricity. " But the electrometer of Coulomb is free from this defect. It is represented in the margin. It consists of a glass vessel having a lid also of glass, in the centre of which a small hole is drilled. Through this hole passes an untwisted raw silk thread four inches long, and fixed at the top to a micrometer, by means of which it may be turned round any number of degrees at pleasure. To the silk thread is attached a very fine gum lac thread, H, having at "^ s^^ A each extremity a small knob. This lac needle with its knobs weighs only one-fourth of a grain. A small hole is drilled in the ^"" ~\ side of the vessel, at A, through which passes a fine wire termi- ^sbs^^ nated at both extremities by a knob. When an excited body is placed in contact with the knob at A, the knob at the other ex- tremity will acquire the same electricity as the excited body. This electricity it will communicate to the knob of the lac needle suspended by the silk thread which was previously almost in contact, and the two knobs will repel each other. The moveable knob attached by the silk thread will separate from the other, and the quantity of electricity will be proportional to the distance to which it is driven off. " Coulomb's electrical balance is an instrument intended to measure the quantity of electricity in bodies, and indispensable in accurate experiments." It should be understood that in this instrument, the knob of the suspended nee- dle may be made to resist sufficiently its removal from that supported by the wire, by twisting the silk in fibre. Coulomb contrived a more perfect and complicated electrometer, upon the same principle as the one which I have described, but fur- nished with graduated circles for measuring the distance between the balls, and the extent of the torsion given to the suspending filament.* By means of this apparatus, Coulomb confirmed an observation, previously made by the Earl of Stanhope, that the density of electricity in the electrical atmosphere, surrounding an excited body, diminishes inversely as the square of the distance from the charged body. Coulomb inferred, from the law thus assumed to exist, and from ingenious and accurate experiments tending to corroborate his inference, that the electricity accumulated about a conducting body is entirely superficial, none of it existing in the interior of the body. He also, as Dr. Thomson conceives, " proved by very simple but convincing experiments, that electricity deposites it- self upon bodies according to their surfaces ; that it has no more attraction for one body than for another: also, that if two bodies, having the same surface, be placed in contact, whatever their nature may be, any electrical surcharge in either will be divided equally between them." Allowance is to be made for the obstruction arising from the diversity of conducting power, which, however, only delays the equalization, but does not prevent it from taking place. * The description of this last mentioned instrument, with engravings, occupies three pages in the Treatise of Dr. Thomson, alluded to above; which is more space than I deem it expedient to devote to the same purpose. ?da 31 OF THE EFFECTS OF ELECTRICITY. The separation or approximation of electrified bodies, the extrication of light and heat, and the shock given to the animal frame, having been all, more or less, subjects of discussion, or adduced as the means of experimental illustration; it may now be proper to display a greater variety of electrical phenomena, and such as being more complicated require undivided attention in those who would comprehend them. OF ELECTRICAL ATTRACTION.—OF ELECTRICAL LIGHT.—OF ELECTRICAL IGNITION.—OF THE ELECTRICAL SHOCK. OF ELECTRICAL ATTRACTION. Under this head are placed both the separation and ap- proximation of light bodies, when electrified; since the former, though commonly ascribed to repulsion, is really, as I conceive, the effect of attraction. 30. REVOLUTION OF A SUN, PLANET, AND SATELLITE. A hollow brass globe, Fig. 1, is rendered much heavier on one side by running into it a quantity of mol- ten lead, sufficient to occupy about one-third of the cavity. By these means when supported on a pivot it preserves a proper position although on the other side not furnished with lead, it is made to support an arm and two balls; one, larger, repre- senting a planet, the other smaller, representing its satellite. These are carried upon the different ends of a wire passing through their axis, and balanced upon the point of the arm, so that the balls may counter- poise each other. From the larger arm, and from the smaller ball, points, P, P, project as represented in Fig. 2. Fig. 2. Fig. 1. trique," a name which I have used for want of a better. It consists of several sets of branches formed of wire. Each set is associated by a common hol- low brass cone, into the apex of which, a recurved wire, forming a principal branch of the electrical tree, is so introduced as to form a support and a pivot, upon which, the cone and its branches may rotate. Each rotatory branch is recurved, and terminates in a point; the points in each set pro- jecting in the same direction, so as to co-operate in producing a circular motion. The branches are put into ope- ration by communicating with the machine, as usual, by the rod, R. The excitement thus recei ved, can- not pass off by the trunk, C, which is of glass, cemented into an up- right brass rod above, and the pe- destal, P, below. It can hardly be necessary to add, that the rationale of the rapid rotation of each set of the branches is analogous to that of the preceding experiment. In consequence of their being similarly surcharged with electricity, or similarly deficient, the adjoining neutral medium attracts the air, and the branches apart, with energy, and thus causes them to recede from each other as soon as they come into proximity. To render the Franklinian rationale more intelligible, as applied to this experi- ment, and that of the miniature sun, earth, and moon, it may be observed, that the excitement of the machine being communicated by the sliding rod, R, to the cen- tral ball, and of bourse to all of the metallic wires therewith associated ; it is dif- fused through the points to the air in their vicinity. Consequently the points P P, and the air electrified by them, being similarly surcharged, or similarly defi- cient, must be attracted by the adjoining neutral medium; and not attracting each other, they are made to separate rapidly, or to move in opposite directions. This process being reiterated with inconceivable speed, the revolutions proceed with proportionable velocity. ^42P 33 32. ELECTRICAL HAIL. This experiment, which is in Pixii'a Catalogue described as " Grele Elec- trique," (electrical hail) affords ano- ther illustration of the movements which may be produced in light bo- dies by electrical attraction. A me- tallic rod supports one ball within the bell glass, another without, so as to be in contact with the knob of another rod, R, proceeding from the conductor of the large electrical machine in ope- ration. The brass ball being by these means intensely electrified, attracts some of the pith balls which lie upon the metallic dish in which the bell is situated, and which should communi- cate with the cushions of the machine. As soon as the pith balls come into contact with the electrified ball, be- coming similarly excited, agreeably to the general law, they recede from each other, and are attracted by the oppo- sitely electrified dish. Reaching the dish they attain the same electrical state' as at first, and of course are liable to be attracted again. Meanwhile other balls are undergoing the same routine, producing that contrariety of move- ments which characterizes the fall »f hail. ELECTRIC LIGHT ILLUSTRATED. 33. Experimental Illustration of the egress and access of the electric fluid during the charging and discharging of coated surfaces, as ren- dered evident by means of a discontinuous coating of metallic filings. The charging and dis- charging of a coated pane, has already been illustrated and explained. The process is however rendered much more in- teresting, when, instead of a continous coating of foil, a covering of metal- lic filings is applied, so as to leave a multitude of minute intervals be- tween the particles of the metal. It is only neces- sary to have the discon- tinuity of covering on one of the surfaces; the other ** may be coated with tin foil, as usual. The tin foil coating should, by means of a strip of the same substance,* communicate with the ring attached to the wooden frame in which the pane is secured. Let the pane, thus prepared, be suspended by the ring, as represented in the engraving, from a rod affixed to the conductor of a powerful electrical machine in operation. As represented in the figure, Jpt a discharger be so held, in contact with the surface coated with filings, 34 as to carry off electricity from it, allowing the other surface of the pane to be proportionably surcharged. In the next placq, let the discharger be so situated, as to qomplete the circuit between the surfaces, allowing the sur- charge in the one, to rush to the other. By these means the efflux, and afflux of the electric matter, will be indicated by corruscations of electric light, with an indescribable splendour, which will appear so long as the surface coated with tin foil, remains in communication with a machine suf- ficiently active, and the situations of the discharger are alternated, as above described. 34. EXPERIMENTAL ILLUSTRATION. Analogous results may be obtained by means of a jar represented by the adjoining figure, which has a hook wnerewith to suspend it; or still more advantageously by means of a large carboy, sil- vered by an appropriate amal- gam within, and on the out- side furnished with a discon- tinuous coating of filings. If the discharger employed in this experiment hare a glass handle, either the me- tallic socket, S, into which the handle is cemented, must be touched by one of the fin- gers, or a wire must be at- tached to it, making a com- munication with the negative conductor, directly or indi- rectly. Otherwise, the external eoating being insulated, electricity could not es- cape from it, and of course the inner surface could not be charged as already de- monstrated. 35. EXPERIMENTAL ILLUSTRATION. The adjoining cut represents a green glass carboy of about five gallons in ca- pacity, coated internally by means of the amalgam usually employed for the purpose, externally by brass filings, as in the cases of the pane and phial above described. It is situated under the pro- jecting ball, B, of the prime conductor, so that the knob at the top of the rod, proceeding through a cork from the in- ternal coating, maybe in contact with the sliding rod, R, of that conductor. The wire, W, is supported on a pedestal in contact with the external coating of the carboy, and in communication with the negative conductor of the machine. Hence, when by the operation of the electrical machine, the internal surface of the glass is becoming charged; the escape of the electricity from the ex- ternal surface is indicated by corrusca- tions of light, and snapping sounds, as in the preceding experiments; and a.t* the instant when the charge acquires sufficient intensity to jump through the interval between the knob attached to the ball, B, and that supported by the wires, the defieit created in the exter- nal surface, being restored at once, the COrrUSCationa anH annrti;n™ „..„ „__*: 35 36. LONG ZIGZAG OR ERRATIC SPARK, CONTRASTED WITH THE SHORT STRAIGHT SPARK. The object of the following engraving is to represent the different forms and lengths of the electric spark, which take place between a large and a small ball, accordingly as they are made negative or positive. The long and zigzag, or erra- tic, spark, A, takes place between a small ball attached to the positive pole, and a large one associated with the negative pole. The short straight spark, B, is eli- cited under circumstances the reverse of those just mentioned. They are repre- sented as simultaneous, but with the same machine, can, of course, only be obtained in succession. In no respect do the phenomena of me- chanical electricity appear more favoura- ble to the Franklinian theory, and more inexplicable, according to the doctrine of two fluids, than in the diversity of the electric spark in passing between a small and a large metallic ball, according to the manner in which the balls are associ- ated with the positive or negative poles of the machine. When the small ball is attached to the positive pole the spark is long, comparatively narrow, and of a zigzag shape, such as lightning is often seen to assume; but when the situation of the balls is reversed, the spark is straight and thick, not one-third as long, and nothing of a zigzag shape can be ob- served in it. According to the Franklinian theory, when any body is more highly charged with electricity than the adjoining bodies, the excess of the fluid is attracted by them, while it is inadequately repelled by the inferior quan- tity of the electric fluid, with which they are imbued. It follows that when a small globe is made positive in the neighbourhood of a large one, the excess of electric matter in the lesser, is attracted by all the negatively excited metal in the larger globe. When the small globe is made nega- tive, the metal of which it consists attracts all the electric matter in the large globe. Hence there is this difference in the two cases; the smaller ball being positive, a comparatively small moveable mass of electric mat- ter, is attracted by a large immoveable mass of metal: the small globe being made negative, a large moveable mass of electric matter is attracted -♦by a small immoveable mass of metal. The charge being in both cases the effect of the same machine; the attractive power must be as great in one case, as in the other. The forces, by which the masses are actuated, being therefore equal, it is quite reasonable that the greatest projectile power should be attained, when the moveable mass is smaller. In that case it will require less air to be removed in order to effect a passage. 36 There is an analogy between the difference which I suppose to exist in the case under consideration, and that which exists between the penetrating power of an instrument which is blunt, and one which is pointed. It remains to show why the large mass of electric matter attracted in a large globe by a small metallic globe negatively excited will be discharged in a spark when there is sufficient proximity, as at B, in the figure, al- though otherwise it will not pass. It must be evident that attraction in- creases, as the distance between the bodies which exercise it, lessens. Of course the attraction of the small globe must always act more powerfully on those portions of the electric fluid which occupy the nearest parts of the positively excited globe. But this'difference of distance, and conse- quent diversity of attraction increases, as the smaller globe approaches the larger. Thus that portion of the electric fluid which sustains this pre- eminent attraction will be accumulated into a cone the acuteness of which and attraction causing the acuteness, increasing with the proximity, there will at last be sufficient projectile and penetrative power to break through the air, and thus open a passage for the whole of the quantity attracted by the negative ball. When by the process last described, the fluid is made to leap through a comparatively small interval by the concentrated attraction exercised by a small negative ball upon the expanded surface of electric matter diffused through a large globe, the air does not become sufficiently condensed to resist it before it reaches its destination, and of course it cannot assume the erratic form which would arise from repeated changes in its course, as in the instance of the long spark. 37. OF THE ELECTRICAL BRUSH. When the machine is in active operation, and the prime conductor insulated; from a small knob attached to it, as at B, in the figure, the electricity will be so sent off, as by the concomitant light to exhibit the form of a luminous brush as represented in this figure at B. For the produc- tion of this phenomenon it is necessary that the electric fluid shall be condensed into a small prominent mass, so as, agreeably to the preceding explanation, to have great penetrating power. This it cannot possess, when with the same intensity in the generating power, a large ball is positively electrified. In that case, the 'electric column presents a front too broad to procure a passage through the surrounding non-conducting air. A small ball, nega- tively electrified, can only be productive of a diffuse attraction for the elec- tricity in the atmospheric medium around it; so that it has less ability to create any penetrating power, than when acting upon the electricity in a comparatively large globular conductor, as in the preceding illustration. Hence when the knob is on the negative pole, it may be productive of a luminous appearance in its immediate vicinity where the electric matter converging from the adjoining space becomes sufficiently intense to be productive of light; but it does not produce the striking appearance of the luminous brush. As agreeably to Du Fay's theory, the knob, whether vitreously or resi- nously electrified, is surcharged with an electric fluid, the projectile power ought to be as great in the one case as in the other; and the long spark, and the brush, should be producible in either case. 37 38. GLOBE, ILLUMINATED PANES, AND TUBES. No. 1. No. 2. Little disks of tin foil are so pasted in succession on a glass globe, pane, or tube, as to leave only a minute interval between them. In con- sequence of this arrangement when situated in the circuit between* jfhe poles of an electrical machine, the electric fluid availing itself of the con- ducting power of the metal, and leaping over each interval, produces as many sparks as there are intervals. At the same time, if these intervals fall within the lines of any drawing, the image representing the drawing will appear at each flash, and when, as in using a large machine^ the flashes are incessant, remitting, without intermitting, the effect upon tfie eye is nearly as permanent, as if the illuminated spaces were inherently luminous. I In the case of the globe and tube, represented by fig. 1, and fig. 2, the disks are arranged in spirals winding about the globe or tube from one apex, or end, to the other. However intricate the route which ingenuity may, by means of the foil, prescribe, when the air and pane are dry, it will be pursued by the fluid with fidelity. Yet the sum of the intervals must jiot exceed the whole striking distance of the machine, or in other words, the greatest length of its spark. This illustration may be varied by means of apparatus, of which engravings and descriptions will be found in the two following articles. 38 39. ILLUMINATED COLUMNS. A iwivel of wire, terminating in knobs, is so balanced upon a pivot, that, when e. 11 chlorine in a like predicament. The impropriety of designating the substances comprised in his halogene and amphigene classes, with the exception of oxygen as combustibles, upon tKe basis of their susceptibility of oxidizement, must be evident from the fact, that fluorine is not oxidizeable, while it is so perfectly analogous to the others, especially chlorine, in its properties, that it would be disadvantageous to class it apart. Berzelius objects to the use of the word " comburant" (equi- valent to the English word supporter) upon the ground that the same substance may alternately be a supporter and a combustible. I should, however, go farther, and likewise object to the use of both words, as tending to convey the erroneous impression, that in combustion, one of the ponderable agents concerned, performs a part more active than the other; whereas, in all such cases, the re- action must evidently be reciprocal and equal. I have repeatedly shown to my pupils, that a jet of oxygen burns in an atmosphere of hydrogen, as well as a jet of hydrogen similarly situated in oxygen. I would recommend that all the bodies comprised in the halo- gene and amphigene classes of Berzelius, should be placed under one head, to be called the basacigen class; indicating their com- mon and distinguishing quality agreeably to the premises, of pro- ducing both acids and bases. The electronegative compounds of these substances to be called acids, their electropositive compounds, bases, as already suggested.* * Since the preceding letter was ready for the press, the following remark of Berzelius attracted my attention, as sanctioning indirectly the definition which I have proposed, page 5. Treatise, Vol. 3, page 323, he alleges—" It follows from this that the property of playing the part of an acid, is attached neither to the substance, nor to the manner in which the combination takes place. It only indicates a state contrary to the property of being a lose."