MODERN VIEWS OF MATTER OLIVER J. LODGE, Liverpool. HSKED to write on the subject of Physics and Physiology, I essayed the task, and mechanism and detail of nerve trans- mission, and the like; for it is clear that all nervous action has an electrical concomitant; and an examination of the question whether the connection between the electro-motive force and the nervous impulse be accidental or essential, and what is the mechanism of transmission, is clearly an important enquiry. Physiologists of late years have made so much use of delicate electrical instruments, they have directed so much attention to electrical manifestations in muscle and nerve, and these electrical effects have proved so useful a test and record of nerve phenom- ena, that it is just possible in some instances that they may have acquired an aspect of over-great importance, that they may be thought of as the real phenomena themselves, instead of possibly only an accompaniment of relative minuteness and insignifi- cance,—a secondary adjunct which is only made manifest because of the extreme delicacy of modern electrical instruments of research. The important thing to attend to about a nerve is the method whereby the impulse travels from place to place, the processes occurring in its substance which fit it for its purpose. What is THE INTERNATIONAL MONTHLY. 494 clear is that this is not of the nature of an ordinary electric current, not even of an electric current in a bad conductor. A message can be delayed to any extent by replacing a telegraph wire by a bit of wet string, but the process of signalling through a few yards of string or cotton, with a high electro-motive force to drive the signal, is not analogous to the process of signalling through a nerve; for the nervous impulse has a definite velocity, slow no doubt but definite, and at any instance at a given place it has either arrived or not arrived. The disturbance passes a given place at definite speed, and with an intensity the same all along and almost proportional to the initiating stimulus. But with an electric pulse travelling along the string it is different; that has no definite speed of travel, it is of the nature of a diffusion. Its detection at a distant end is simply a question of the sensitiveness of the receiving instrument. If that were infinitely sensitive it would be detected at once, or at least with the speed of light; whereas if the receiver will not respond except to a considerable potential, or a considerable current, it may not be able to respond at all ; or supposing that it is able to respond ultimately, the lapse of time before it responds may be anything, from one hundredth of a second to a minute or an hour. Some infinitesimal disturbance arrives at once, and then gradually increases in strength until it can be detected. The travelling of a wave or of a nervous impulse is entirely different from this, its arrival is more like that of a bullet,—which has either not come at all or come wholly. The laws of the conduction of electricity along a well insulated string are precisely the same as those of heat flowing through a slab, or along a bar well wrapped in cotton wool and protected from cooling influences. If cooling is allowed, then a similar allowance must be made for the string, if the analogy is to be preserved, that is to say, the string must be allowed to leak slightly all along its course. Moreover there is another difference. As I understand the MODERN VIEWS OF MATTER. results attained by physiologists, the electro-motive force observed in nerve is chiefly radial in direction, that is to say, it acts between the axis of the nerve and its sheath (when it has an axis and a sheath), and barely, if at all, in the longitudinal direction. It does not seem certain that it has any longitudinal component at all, although it is transmitted in that direction. It appears to be transmitted sideways, it is set free or displayed by the agency of something which travels along the nerve, but this agency does not appear to be electro-motive in the ordinary sense; there does not appear to be a longitudinal gradient of potential; what gradient of potential there is appears to be radial, from axis to sheath, or vice versa. A stimulus applied at any point seems to make the core of the nerve positive to the outside, and this difference between them seems to excite or transmit an impulse longitudi- nally, which as it arrives sets up momentarily a similar difference or negativity of the outside : giving rise to a momentary change of potential which can be detected by the terminals of a galvano- meter or electrometer applied to the nerve at any two points ; but the agency which travelled, and liberated the electricity so to speak, remains just as much in the dark as before1. 495 (i) A few ideas as to possible modes of nerve transfer occur to a physicist, and may conceivably be suggestive to physiologists who have a vastly greater acquaintance with the facts to be explained. Without apology, therefore, I would suggest that perhaps a nerve fibre has not a conducting structure at all, but a capacity structure. It has a leakage conductance, corresponding to that of any other thread moistened with weak saline liquid, but no specific or effective nervous conductance ; but it has, I suggest, a radial capacity, as if it consisted of a series of cylindrical condensers packed end to end. A longitudinal capacity too, very likely, with all the condensers in series, provided they are not insulated from each other, but that is insignificant in comparison with the radial capacity, by reason of the enormous number of them in a small length. Such longitudinal capacity would show itself as a kind of polarization when a steady current is driven along the nerve, each condenser becoming slightly charged ; a reversed current should therefore for the first moment flow more easily ; and to an alternating current the extra polarization resistance would not be offered. I have heard that an alternating current along a nerve does experience a somewhat lower resistance than a steady current ; but if so the true conductance of the nerve fibre, considered as an ordinary conductor, would be correctly measured by the 496 THE INTERNATIONAL MONTHLY. Yet until this agency is brought to light all the physics of nerve physiology remains in a crude and imperfect state, and the physiology of special organs of sense cannot be completed ; because in seeking how it is that peripheral organs receiving the energy of an external stimulus convert it into that which is appropriate to be transmitted along the nerve, we can have little hope of being able to solve this question until we know what form of energy it is which is thus capable of travelling. That either a mechanical, electrical or chemical stimulus will excite a nerve is true enough ; but the statement is no more theoretically illuminating and informing than the equally true statement that if you make a body hot enough it will emit light, without any attempt to explain what light is, or by what process it is emitted, nor why nor how heat energy (that is molecular vibrations) can be converted into light energy (that is etherial waves). But then physicists must admit that a very short time ago this latter explanation could hardly have been given with any precision, —indeed even now it cannot be said that the details of the process are thoroughly clear or free from points of legitimate steady current,—the current it is able to transmit when its polarization is complete,—that is when all its condensers are full. The apparent extra conductivity shown by a nerve to an alternating current would not be true conductivity, but would be a capacity effect. If R is the resistance measured by a long continued steady current ; if R1 is the resistance offered to an alternating current of frequency p/V77", and if there are n condensers in series each of longitudinal capacity s/k ; then j_ — J_ i _ps R1 R ' nk But the individual radial capacity would probably be greater than s/k, say s ; and the aggregate radial capacity would be estimated as n* k (R—R1) S ~ nS ~ pRR1 ' I would suggest further, that on the arrival of a stimulus each nerve segment becomes momentarily charged,—negative outwards, positive inwards,—and that then it discharges into the next, charging it in the same way ; and that controversy; only steps towards an explanation have been made, and some of them have been made within quite recent years, —some within the last two years; hence it is no wonder that the more difficult question, by what means a nervous impulse is excited by a physical mechanism, or what it is precisely which goes on in a nerve and how it is excited by a mechanical or elec- trical stimulus to the peripheral organ, still remains unanswered. In attempting, not to answer it but to indicate some facts which must probably be taken into account before an answer can be formulated, I find myself involved in an entanglement of recent research into the structure of matter and the nature of what has been called the ultimate atom, out of which sooner or later something is bound to emerge in the physiological direction, though what that something may be I will not attempt to predict. I will merely say that the fact that a cathode—a negative terminal —is the most active stimulus for a nerve, will be seen to derive some possible illumination, or at least to be rather suggestive, in the light of what follows. The facts and researches to which I allude are not however as yet generally known, and possibly have not (the most recent of them) even been heard of by physiologists; so I propose to utilize the space allotted to me by an attempt to sketch the main MODERN VIEWS OF MATTER. 497 into the next, and so on, until the last discharges into and stimulates the muscle. The conditions for the discharge might very possibly be the dead- beat condition L—JSR2. The time-constant of each condenser would depend on the product of its resistance and capacity, and so its order of magnitude would be sR/n. This represents something like the time required to charge and discharge the condenser, with whatever electromotive force may be available in its structure: the source and seat of the E. M. F. being a matter on which I shall be silent: though the partial similarity of nerve electricity and muscle electricity, and the ready modification of muscle into an electric organ, suggest that such an E. M. F. is certainly forthcoming from live organic tissues. The time taken to travel along a length of nerve having n condensers end to end, would therefore be of the order Rs, which could be measured as n k (R—R1) p R1 498 THE INTERNATIONAL MONTHLY features of this new territory now being conquered for science. Preluding my account however with the proviso that some of it is held on a less secure tenure than other parts, and that though I do not wish to represent as established anything which is still liable to successful hostile attack, yet I shall represent what seems to me at present to lie in the direction of the truth, though at the same time fully admitting that hostility to some of it will be felt by some physicists, and probably by many chemists for a long time to come. For it lies on the frontier of both sciences and no doubt will form a battle ground between physics and chemistry for many of the early years of the twentieth century ; just as in the early years of the present century there was a long discus- sion and controversy as to the acceptance or rejection of the atomic theory of John Dalton. It is not to be supposed for a moment that because the atomic theory generally has made its way into universal acceptance, therefore every detailed view of Dalton was correct and substan- tiated ; clearly there must be distinctions. Dalton’s view of the elasticity of gases, for instance, was a statical view based on the idea of molecules at rest, each surrounded by an elastic atmos- phere and so pressing outward against each other and against the sides of the vessel, thus raising a piston, or the lid of the vessel after a spring jack-in-the-box fashion. This was really no explana- So the velocity of an impulse along a nerve would be p R1 V ~ n, k (R—R1) ’ Where nn is the number of condensers in unit length of nerve $ and this velocity can be made as small as experiment requires, by postulating a sufficient value for nn. Suppose, for instance, the resistance measured by a current alternating one thousand times a second came out one per cent less than the resistance to a steady current, and suppose the velocity of propagation of a nervous impulse was thirty metres per second, then the number of cells or condensers per centimetre of fibre would have to be of the order two hundred, provided the longitudinal capacity and the radial capacity of each were approximately equal. These numbers are quite gratuitous. MODERN VIEWS OF MATTER. tion of elasticity at all, but it might have served as a statement of the fact of gaseous pressure, had it been true that the atoms of a gas were stationary and surrounded by infinitely expansible elastic atmospheres or repulsive forces. But as is well known these things were not true, and gaseous pressure and elasticity are now explained, not statically at all but kinetically, as due to a bombardment of free atoms, perfectly dis- connected from one another except during moments of collision. Nevertheless this is a detail, and the general doctrine of the existence of atoms is universally accepted. A lump of matter is as surely composed of atoms as a house is built of bricks. That is to say, matter is not continuous and homogeneous, but is dis- continuous ; being composed of material particles, whatever they are, and non-material spaces. There is every reason to be cer- tain that these spaces are full of a connecting medium, full of ether; there is no really void space; and the question may be asked, is this ether not in a manner itself “ substance ” ? Is it not matter in another form ? To this I should reply, and I sup- pose all physicists would reply,—“ substance ” it may be, “ mat- ter ” it is not. Not matter as we know it, not matter in the sense we use the term. That term is limited, I take it, to the material bodies which are built up of atoms; it does not extend to the substance or medium, whatever it may be, occupying all the rest of space. This is only a question of nomenclature, and therefore of no great importance, but that is the sense in which the terms are, here at any rate, employed. When I say that matter is certainly atomic I by no means mean that ether is atomic. I hold that ether is most certainly not atomic, not dis- continuous ; it is an absolutely continuous medium, without breaks or gaps or spaces of any kind in it,—the universal con- nector,—permeating not only the rest of space, as I have just said, but permeating also the space occupied by the atoms them- selves. The atom is a something superposed upon, not substituted for, the ether, it is most likely a definite modification of the 499 THE INTERNATIONAL MONTHLY. 500 ether, an individualization, with a permanent existence and a faculty of locomotion which the ether alone does not possess. Matter is that which is susceptible cf motion. Ether is that which is susceptible of stress. All energy appertains either to matter or to ether, and is continually passing from one to the other. When possessed by matter the energy is called kinetic : when possessed by ether the energy is called potential. All the activity of the material universe is due to, or represented by, or displayed in, the continual interchanges of energy from matter to ether and back again, accompanied by its transformation from the kinetic to the potential form and vice versa. And having asserted this, which I have said at greater length elsewhere, [“Philadelphia Magazine”]; and adding the proviso that not by all physicists is it as yet, so far as I know, universally accepted ; I shall henceforward discard further reference to the ether, in this essay, and shall deal with matter alone. Matter consists of atoms, or molecules ; for present purposes there is no need to discriminate. Chemically it is convenient to attribute slightly different meanings to the two terms, but the distinction is of the easiest and most elementary character. A molecule is the smallest complete and normal unit of any sub- stance, it consists usually of two or more atoms, though it may consist of one; and what we have to say here relates essentially to the atom. Is the atom an ultimate atom ? Is it really and truly indivisible, is it an ultimate element or unit which cannot be split up into parts; or does the customary postulate of its indivisibility mean no more than that we have not yet succeeded in discovering a way of decomposing it; or again does it mean that if we did by any means break it up into fragments it would no longer be an atom of matter but something else ? Suppose for a moment that the atom was a vortex ring in ether, for instance, which could not be split up without destruction ; the splitting up would not destroy the substance of which the ring is composed, but it would destroy MODERN VIEWS OF MATTER. the motion which constituted it a ring, which gave it individuality ; it would destroy everything which entitled it to the term “ matter.” If broken up it would be resolved into ordinary ether, as a dispersed smoke ring loses its individuality in common air. A common vortex ring of air or water contains within itself the seeds of its own decease; it is composed of an imperfect fluid, possessing that is to say viscosity, and accordingly its life is short; its peculiar energy being dissipated, its vortex motion declines, and as a ring it perishes. But imagine a ring built of some per- fect fluid, of some medium devoid of viscosity, as the ether is ; then it may be immortal; it can neither be produced nor anni- hilated by known means; and it is just this property, combined with other properties of elasticity, rigidity, and the like, that led Lord Kelvin originally to his brilliant and well-known hypothesis. In the crude form here suggested, the hypothesis has not turned out exactly true; that is to say, no one believes now that an atom is simply a vortex ring of ether, and that the rest of the ether is stagnant fluid in which the vortex rings sail about. Any quantity of difficulties surround such an hypothesis as that. Its apparently attractive simplicity is superficial. Nevertheless it is not to be supposed that every hydro-dynamical theory of the universe is thereby denied. It is quite conceivable that a single fluid in different kinds of motion—some kinds of motion not yet imagined perhaps—may possibly be found capable of explaining all the facts of physics and chemistry :—whether of biology too is a much larger question. But these hydro-dynamic explanations are a step beyond anything that I propose to discuss now. I have only said as much as this in order to make it clear that what we now go on to, even if it were completely true, must not be held to replace and negative all the attempts that have been made, and that still will be made, to account for material phenomena by the motions or strains of a perfect fluid. I may as well say however that the motions that must be postulated will have to be 501 502 THE INTERNATIONAL MONTHLY. of a far finer grain, the individualization on a far smaller scale, than the original vortex-atom view, which was one vortex ring for each atom, and differently shaped or tangled rings for the different elemental atoms. If there is to be vorticity at all, it would appear that the whole ether must be full of it; it cannot be a simple stagnant, structureless, homogeneous fluid for that would not transmit light,—would not account for optical phenom- ena even, still less for those of static electricity and magnetism. Unintentionally we have drifted back to the ether again, whereas I want to concentrate attention on the atom of matter. Is it indivisible or does it consist of parts ? If so, how many and what are they ? Can one of them be detached from the rest of the atom and observed ? Can the motion of a fraction of the atom be detected and measured ? Can the atom be broken up, and its constituent parts dealt with ? If different kinds of atoms are broken up will they yield fragments of different kinds, or will they all yield fragments of the same kind ? Can the fragments move at a measurable speed, and can the effect of bombardment, when they are stopped, be observed ? Are the fragments all alike, and can they be weighed ? Are they, or can they be, charged with electricity ; and if so what properties do they possess when so charged ? Can an atom be charged, and if so, how ? When a current of electricity is conveyed, by what mechanism is it transmitted ? Can its phenomena be always accounted for by the transport of an electro-static charge ? What is meant by the inertia of matter ? Has electricity an existence apart from matter ? What is the relation if any between a unit of electricity and an atom of matter ? All these questions appear to be capable of receiving an answer; they also appear to me to be in process of being answered; and I would not say too much about the impossibility of an answer being given to some further questions before long, but they are in a different category from these, and involve a higher order of difficulty. The question, what is the nature of MODERN VIEWS OF MATTER. an electric charge, for instance, is not among the questions which are in process of being answered with any certainty or with any simplicity just yet; it will probably remain for some years yet a question and a challenge. Nor is the answer, when it comes, likely for a long time to be an easy one, such as it is possible to state in general terms and ordinary language. The existence of an electrical charge we must assume: a charged body is a fact; whether a charge can exist without a body is doubtful, but in any case we shall assume that the properties of an electric charge are those which we know and are familiar with by experiment upon ordinary large pieces of matter positively and negatively electrified. What are these properties ? They are best expressed, in Faraday’s language, as a “field of force,” a region full of lines of force, every line necessarily starting from a positive charge and ending in a negative one; no line closed upon itself, every line two-ended, every positive charge being connected with an equal negative one ; no possibility of having plus electricity without minus electricity, any more than it is possible for one end of a piece of string to exist without the other end. This fact, the existence of positive and negative charges, we must assume too : they exist, they have opposite properties, they are like opposite aspects of the same thing, or opposite elements of one compound ; or opposite strains (as J. Larmor puts it)—a right-handed and a left-handed strain in the ether. Whatever they are they exist, and their explanation must be waited for. The charges themselves are after all only the terminals or boundaries of the field : the whole field of force itself is the most real thing ; one cannot say that the charges are the cause of the lines of force, or the lines of force the cause of the charges, they simply co-exist. The lines of force represent a structure of some kind in the ether, they need no “ matter ” for their existence, they can penetrate what we call absolute vacuum, they are clearly an etherial phenomenon ; but what about their ends ? Can they 503 THE INTERNATIONAL MONTHLY. 504 terminate except on an atom of matter? The answer is uncer- tain, but at any rate we can say this, that never experimentally have we known them to terminate except on a material body. From body to body they reach, and one of the bodies is positively charged, while the other is negatively charged. That is what, at least to begin with, we must assume as universally true. The manner of starting such lines into existence is familiar. Any two different bodies put into contact and separated will usually be found joined by such a field of force, provided precau- tions are taken that the ends shall not slip or leak away back to each other during the separation process. Once the field is established, it may be carried about; but it has gradually become clear that the field is carried through the ether and not with it; in other words the field is not really moved, it is truer to say that it ceases in one place and starts in another, that as a charged body moves about its lines of force are perpetu- ally decaying on the side of recession, and being generated on the side of approach; continuing constant in number, so long as there is no leakage, but not possessing individuality of existence. The abandoned region of ether is relieved from strain, and the encroached-upon region sustains the strain. This transfer of the lines of force has a singular result; a result unguessed by Faraday : a result barely explained even by Maxwell ; it interposes a certain obstacle to change of motion. It does not simulate a resistance, or friction, or force of any kind,—that would tend to bring a body to rest; but it simulates an inertia, the precise opposite of force,—a power of moving where no force acts—a property requiring an unbalanced force to change the motion, or even to stop it. But matter alone, uncharged, possesses this inertia ; the effect of any charge on it is merely to increase the ordinary material inertia or massiveness,— necessarily to increase it, whether the charge be positive or negative, showing that it is proportional to the square of the charge or to the charge and the potential conjointly ;—and the MODERN VIEWS OF MATTER. 505 precise value of the increase has been calculated both by Professor J. J. Thomson and by Mr. Oliver Heaviside. Hence there is discovered a new kind of inertia, an inertia- reaction to mechanical force, obedient to Newton’s second law, but not a measure of quantity of matter as we have hitherto known it. It is not proportional to mass, possibly not susceptible of weight, that is to say, it is not acted upon by the force of gravi- tation ; and yet simulating one, and that the most fundamental of the properties of matter,—the property of inertia,—the property which is measured precisely by the ratio of any unbalanced force acting to the acceleration which it is able to produce. Are there then two kinds of inertia : one material, the other electrical ? What do we know about the material kind ? Very little. It has been accepted as a property which it was vain to attempt to explain,—a property whose presence is inextricably bound up with the existence of matter, and believed to be more essential to it than gravitation. What do we know about the electrical kind ? Not much, but more. In a sense it is intelligi- ble, we can realize how it depends on the field of force sur- rounding the charge; how it is a property not located in the charge or the charged body, but depending on a modification of the ether extending all through space external to the charged body, though concentrated chiefly in its immediate neighborhood, and especially concentrated in the space between two charged bodies close together when these are opposite in sign. That as a fact an electric current, in virtue of its magnetic properties, possessed something akin to, or which simulated, momentum, has been known to science ever since Lord Kelvin wrote that wonderful paper on “Transient Currents” in 1853 > or even since Helmholtz wrote his memoir “ die Erhaltung der Kraft” in 1847. But that this electro-kinetic momentum was due to a real inertia, and that the apparent inertia would hot cease with the current, but would remain as a property of an electro- static charge,—a constant property, whether the charge was in 506 rest or in motion, just as it is a constant property of matter,— was not at that time nor long afterwards known; possibly it was not even suspected. To-day the question to be asked is, whether there is any other inertia at all ? There is certainly the electrical kind,—its mechanism is fairly and to some extent intelligible,—is there any of the material kind ? The possibility of the question represents a curious inversion of the ancient order of ideas, but the question is most seriously asked; though its answer is uncertain. To Dr. Johnstone Stoney it has appeared likely that a charge can exist without the necessary presence of a material atom as a nucleus or resting place. Matter can exist without a charge, why not a charge without matter ? A cat without a smile, as Lewis Carroll says, why not a smile without a cat ? At any rate he has given such an isolated charge of electricity a name— “ electron ” ; that means a unit of electric charge, positive or negative, disconnected from any material body, and of which no fractions are possible, the hypothetical ultimate w atom,” so to speak, of electricity. But we must not be too sure that such detached charges can exist without matter. As electrical units they are known and measured in electrolysis, that is, in liquid conduction of electricity, and there they are certainly associated, and inseparably associated while in the liquid, with material atoms. The whole conveying of electricity through a liquid consists in the convection of the atomic charge by a travelling atom, or it may be, the convection of an atom by its travelling charge. Atoms thus charged and travelling are called “ ions ” : some of them are positive and some negative, and they travel of course in opposite directions along a potential gradient. All this is familiar, and the magnitude of the ionic charge has long been known. Known it is also that hydrogen atoms have one such charge, oxygen atoms two, gold atoms three, and so on. As many as six such unit charges, all of one sign, may, it is supposed, THE INTERNATIONAL MONTHLY. MODERN VIEWS OF MATTER. be possessed by some kinds of atoms,—or as few as none,—but never a fraction. An ionic charge is the irreducible minimum, as it would appear, and was styled by von Helmholtz 14 One molecule of electricity ” : every actual or possible charge being an exact multiple of this unit. Small of course it is, but not small compared with the mass of an atom ; its ratio to the atomic mass is accurately known ; this ratio, the ratio of the quantity of matter to the quantity of electricity, is called the electro- chemical equivalent of the substance ; and was measured first by Faraday,—afterward with greatest accuracy by Lord Rayleigh. Nowadays, through Dr. Johnstone Stoney, Professor Loschmidt, and Lord Kelvin, we know approximately the absolute mass of an atom ; hence we know, with equal approximation, the value of the atomic or ionic charge, in terms of what we call an electro-static unit; and it comes out about icr11 of such a unit per monad atom. All this is the a, b, c, of electro-chemistry. Why then introduce it here ? For the sake of completeness, and as a reminder to those whose physics may be a trifle rusty. Now comes the first question :—is the atomic charge fixed to the individual atom, or can it be passed on to other atoms ? Answer :—in the liquid state the charge is certainly fixed to the atom ; there is no trace of physical or metallic conductivity; true liquid conduction is wholly chemical or convective ; the atom travels with its charge, and at the same rate; the two are insepar- able in the body of the liquid always, whether the current pass from one liquid to another of different composition or not, provided always that no part of the liquid becomes solid, forming an insoluble precipitate. This answer is rendered possible by the careful quantitative experiments of Faraday. It was and has been several times doubted, for good reasons, but for reasons whose other meaning is now understood. But the case is quite otherwise when the matter comes out of solution, as it must when a solid electrode is reached. Then the charge and the atom separate ; the electricity goes one way, 507 508 into the electrode and on through a wire ; its quondam carrier or atom goes another way, into the liquid perhaps, or else stops behind on the electrode, and ultimately, it may be, escapes as gas or otherwise undergoes customary chemical accidents. It is not difficult to picture two or more such atoms, thus planted side by side or superposed in close contact, relieved from the similar charges which kept them asunder, combining, possibly by ordinary cohesion, either with each other or else with the electrodes to which they cling. It is more interesting to follow the freed charge in its progress through the metal. How does it travel now ? There is no convection or conveyance per ion here, it must either make its way between the atoms, or it must be handed on from one to another. The method of transmission is not that of a seed carried by a bird, but that of a fire-bucket passed from hand to hand. And yet not quite or not necessarily like that, for we have no certain means of individualizing the charge as we have the bucket, all we know is that the same amount is passed on ; but an atom may conceivably receive one charge and pass on another of equal quantity,—provided there is any meaning in this attempt at individualization of electricity. There is plainly a temptation to attempt such individualization when it is realized how like an “atom”, in some respects, this unit of charge is. It can be had in multiples but not in fractions, there is a sort of “ law of combining proportion,”—most of the arguments of Dalton for the atomic theory of matter now apply to electricity. Is electricity then atomic too ? Does it also consist of indivisible portions each of definite quantity and all exactly alike ? It is not wise to assert such things too hastily, but that is the appearance which facts present. Dr. Johnstone Stoney, among others, has definitely faced some of the con- sequences of this view of electricity and has supposed that these apparently indivisible units can separately exist as “ electrons ” ; and Dr. J. Larmor has attempted a comprehensive mathematical THE INTERNATIONAL MONTHLY. MODERN VIEWS OF MATTER. theory of the whole material universe on the basis of these electrons as strain centres in an otherwise homogeneous ether. Anyway we must admit that such electrons, whether they have a separate existence or not,—that is whether they can exist apart from matter or whether they only represent a charge existing on a material particle of some kind,—are themselves a great deal more like matter than we might have expected. Considered by them- selves they possess inertia, as we have seen, and are capable of acceleration under mechanical force in accordance with Newton’s Laws of Motions. At the same time an electron is certainly not an atom, for it is capable of being separated from an atom and conveyed one way while the rest of the atom goes the other way. It appears in fact, so far, as only another name for an ionic charge, plus the postulate of individuality and indentity. For when masked or neutralized, the electron is not destroyed but is merely brought face to face with an equal electron of opposite sign ; the distant effects of each are then neutralized until they are once more separated. Electrolytic conduction certainly consists in the travelling together of an atom and its charge, but metallic conduction may be either the travelling of an identical electron from atom to atom, or it may be the reception of one electron and the passing on of another; and this latter view is on the whole decidedly the more probable. Each atom receives a charge from an adjacent one, and passes an equal charge on to the one adjacent on the other side, and this process may readily be accompanied by a slight molecular motion exhibiting itself as a rise of tempera- ture. And if, having the process of interchange of constituents in view, we contemplate what must happen at a junction of two different metals across which a current is flowing, we shall witness a curious interchange or transfusion of substance, but without change of identity, without real transmutation and without combination or alloy. This is not the place to dwell on that 509 510 aspect further : suffice it to say that the modern doctrine of the nature of the atom must have an influence on a vast number of physical phenomena, whether they occur in wires or whether they occur in nerves. But a consideration of metallic conduction would never have given us the conception of an electron. Nor would a study of electrolytic conduction. The latter gives us the notion of an ionic charge, an indivisible electrical unit, but we find it there always associated with an atom of matter. How then have we gained the idea that it may be possibly associated with masses of matter less than the atom, or possibly with no mass of matter at all; how have we got the notion of an electron as a separate entity ? The idea has come to different men in different ways, and we are not now concerned with any historic order; I will take the facts in any order convenient for exposition. A few years ago Professor Zeeman of Amsterdam—one of that race with whose colonial descendants we are sadly and badly and madly at war, for these epithets apply to whomsoever the fault of origin belongs,—a few years ago Professor Zeeman discovered that the lines in the spectrum of incandescent sodium vapor were slightly broadened by the influence of a strong magnetic field applied to the flame, when examined in a spectroscope of adequate power. It was an effect that Faraday had looked for, and failed to find, because it is very minute, and the optical resources of his day were quite inadequate to show it. Nowadays the splendid diffraction-gratings of Professor Rowland of Baltimore make the demonstration (though not the discovery) comparatively easy : and the lines of the spectrum of all sorts of metals are found to be doubled or tripled or quadrupled, or even hextupled, according to the nature of the metal and the individual character of each line. Well, what of that ? The bare fact is not illuminating. No, but no fact is really bare, except in the subjective sense that we have not yet clothed it in theory. In this case the theory was ready, it was provided for it by Larmor THE INTERNATIONAL MONTHLY. and by Professor H. A. Lorentz of Leyden, a brilliant mathemat- ical physicist of the same strong race. By these men and by Fitz- gerald of Dublin the bearing of the new fact was quickly grasped, as well as by Zeeman also, as shown in his correspondence with Lorentz. At once the measured amount of the broadening, the distance apart of the components of the doubling, became the means of ascertaining the electro-chemical equivalent of the radiating matter. Electro-chemical equivalent is a term in elec- trolysis ; what has that to do with radiation ? It signifies the mass of matter associated with a unit charge of electricity. Precisely, but considered from the point of view of Clerk Maxwell’s theory of light it applies to a radiating body also. In order to emit waves into the ether an electric oscillation is necessary; a mechanical oscillation will not do. A radiating atom must contain some sort of vibrating electric charge. It may be that the whole atom, with its ionic charge, is vibrating ; and it may be that an electric charge is surging to and fro on an atom, as it surges on a Hertz-conductor ; or it may be that some fraction of the atom possesses the charge, and that this fraction only is set vibrating, while the remainder is inert. This electric view of radiation, which ever since the time of Maxwell and Hertz has been in everybody’s mind, is proved to be the true one by Zeeman’s phenomena, ;.