-*> IV REESE 'LIBRARY ERSITY "OF.JCALIFQRN IA < No, ^' f~ M\ y tf NEW THEORIES OF MATTER AND OF FORCE. NEW THEORIES OF MATTER AND OF FORCE BY WILLIAM BARLOW HonHon SAMPSON LOW, MARSTON, SEARLE, AND RIVINGTON 1 88, FLEET STREET 1885 \All rights reserved.'} Printed by Hazell. Watson, & Viney, Limited, London and Aylesbury. PEEFACE. A NY one opening this volume will not be likely to proceed far before the question comes into his mind What led the author first to entertain conceptions of the fundamental nature of things which are so unusual, which owe so little to generally accepted theories, and are, in- deed, in many cases antagonistic to these theories? To meet any such questioning, and to satisfy the reader that he is not being treated to some mere figment of the author's imagination, but to conclusions drawn, whether rightly or wrongly, from actual facts, the author would say that the general theory, or cluster of interdependent theories of matter and of force submitted in this volume, result from the careful consideration of the more salient phenomena of the different branches of physics, with the aid of a clue obtained by the author when endeavouring some time since to assign to the luminiferous ether known properties of matter which should be adequate to account for its propagation of light. He first reached a rude theory of the nature of the ether according to which the transmission of wave-motions VI PREFACE. depended on the mutual repulsions of similarly electrified particles, and from this, by degrees, he arrived at the con- ception contained in these pages, of two compressible, elastic, gas-like ethers, adequate, as it will be argued, for the transmission both of light and of electricity. The evolution of this conception was assisted and mate- rially influenced by the discovery that the existence of two ethers of some such description would account for much more than the author at first hoped, and that facts in all branches of physics could be made to yield evidence as to the precise nature of these two ethers. The strongest arguments for the acceptance of some such theories as are here submitted are that they account for all kinds of action at a distance, and also afford an explanation of most of the cases of correlation found sub- sisting among physical phenomena ; and further, which is perhaps the most important evidence of all, that they account for many of the definite quantitative laws and relations of physics and of chemistry. Thus these theories can be shown to account for the law of inverse squares as found in gravitation, the fact that the electrical capacities of similar conductors are as their linear dimensions, the law of refraction known as the " law of sines," the law of reflection, the fact of maximum polarization by reflection taking place when the angle of incidence is such as to give the direction of the reflected ray perpendicular to the direction of the refracted ray, PREFACE. Vll Joule's law for electric currents that the amount of heat generated in a given time varies directly as the product of the resistance of the wire into the square of the strength of the current, the fact that bodies combine chemically in simple proportions, the fact of the simple relations sub- sisting between the gaseous volumes of compounds and of their constituents, and finally for several cases of the association of particular crystal forms with particular chemical groupings. Some conclusions relating to crystallization derived from the following arguments appeared in December, 1883, in " Nature," Nos. 738 and 739, vol. 29, under the heading " Probable Nature of the Internal Symmetry of Crystals." The paper received some approval, but was necessarily too fragmentary for any extended criticism, and it did not contain the fundamental theories at the root of the author's system. The treatment of so wide a range of subjects is of necessity often cursory, and the author does not for a moment suppose that the particular theories reached are final ; all he contends is that the concurrence of the evidence in their favour drawn from such various sources establishes the probabilities that they are at least an advance towards the truth, and that the fundamental suppositions on which they are based are correct. Most readers will probably consider that in some few places the text is unnecessarily burdened with well-known Vlli PREFACE. rudimentary details ; the reason for the introduction of any apparently superfluous matter of this kind is that the author desires to make his book readable as a whole by those who know a little about one or two of the subjects treated, but nothing about others. The author intends at a future time to offer further evidence in favour of his theories, based upon the pheno- mena of crystallization, of meteorology, etc. MUSWELL HILL, March, 1885. CONTENTS PAGE INTRODUCTORY CHAPTER ., , ..... . 1 CHAPTER I. FUNDAMENTAL HYPOTHESES . 5 CHAPTER II. THE LAW OF SYMMETEICAL INTERMIXTURE CHAPTER III. THEORY OF MOLECULAR MATTER THE ELEMENTS ... 14 CHAPTER IV. THEORY OF THE DIFFERENT STATES OF MATTER ... 23 CHAPTER V. THEORIES Oi' GRAVITATION AND CAPILLARY ACTION 39 ELECTRICITY. CHAPTER VI. THEORY OF WHAT ELECTRICITY IS CONDUCTION ... 63 CHAPTER VIT. ELECTRICS AND NON-ELECTRICS. ELECTRICITY LIBERATED BY MOTIONS OF MOLECULAR MASSES. THE TWO ETHERS MOVE IN OPPOSITE DIRECTIONS 73 b X CONTENTS. CHAPTER VIII. ELECTROSTATICS. Attraction and Repulsion CHAPTER IX. ELECTROSTATICS. Continued, Inflation Electrical " Density" and Distribution, ... 86 CHAPTER X. ELECTROSTATICS. f'o/ifi Hired, Electrical Induction Electric Shadow ...... 92 CHAPTER XI. ELECTRO-DYNAMICS. Ether Current x of Short Duration Electric Condensers Effect* of the Presence of tin' 1'nmi.i-ed Ethi rx on Molecular Matter . 105 CHAPTER XII. ELECTRO-DYNAMICS. L 'out in tied. Electric Currents of Long Duration, or Continuing Current*. . 126 CHAPTER XIII. ELECTRO-DYNAMICS. Continued. Electrical lirsixtance Ohm'* Law ....... 150 CHAPTER XIV. ELECTRO-DYNAMICS. Con fi fined. Induction of Currents Attraction and Iteyulxion of Current* . lio CHAPTER XV. MAGNETISM DIAMAGNETISM ....... KJ9 CHAPTER XVI. ELECTRO-MAGNETIC PHENOMENA PHENOMENA OF ELECTRIC INDUCTION ........... 187 CHAPTER XVII. THE ELECTRIC LIGHT 195 CONTENTS. xi PAGE LIGHT. CHAPTER XVIII. THEORY OP THE NATURE OF ETHER WAVES 200 CHAPTER XIX. REFRACTION . . .. ... . . . . 209 CHAPTER XX. REFLECTION OF LIGHT AND FURTHER CONSIDERATION OF RE- FRACTION . . . . . - . * . . . . . 220 CHAPTER XXI. DISPERSION . . , 237 CHAPTER XXII. PRODUCTION OF IRIDESCENCE BY INTERFERENCE DIFFRACTION COLOUR PRODUCED BY THE PRESENCE OF DUST OR SMALL PARTICLES .''.. I .'-;.. . . . - . . 246 CHAPTER XXIII. COLOUR PHOSPHORESCENCE AND FLUORESCENCE TRANS- PARENCY . . . , . . ..... . . 257 CHAPTER XXIV. DOUBLE REFRACTION AND POLARIZATION 271 CHAPTER XXV. DEPOLARIZATION COLOURS OF POLARIZATION ROTATION OF PLANE OF POLARIZATION, ETC 286 H E A T. CHAPTER XXVI. DIFFERENT ASPECTS OF THE PHENOMENON OF HEAT HEAT AN AGENT WHICH PRODUCES CHANGE OF BULK OF MOLECULAR MATTER THERMOMETRY 300 Xll CONTENTS, - PAGE CHAPTER XXVII. '! "J it THEORY OF HEAT RADIATION . . ^ *. ^ s- . . . 308 CHAPTER XXVI1L CONDUCTION HEAT PRODUCED BY ELECTRICITY HEAT PRO- DUCED BY FRICTION. . . . ..... 316 CHAPTER XXIX. THE EFFECT OF HEAT IN PRODUCING CHANGE OF STATE . . 324 CHAPTER XXX. CALORIMETRY. Specific Heat. Latent Heat ........ :ii"J CHEMISTRY. CHAPTER XXXI. SYMMETRICAL INTERMIXTURE OF THE ELEMENTS . . . 337 CHAPTER XXXII. CHEMICAL SYMBOLS AND TECHNICAL TERMS 343 I'HAI'IEU XXXIII. ADEQUACY OF THE LAW OF SYMMETRICAL INTERMIXTURE TO PRODUCE VARIOUS KINDS OF ATOM COMBINATION SUCH AS OCCUR IN DIFFERENT CHEMICAL CHANGES . . . . olb CHAPTER XXXIV. THEORY OF THE PRODUCING CAUSES OF CHEMICAL CHANGES APPLICATION OF THE THEORY TO SOME CASES OF SYNTHESIS AND METATHESIS QUANTIVALENCE 370 CHAPTER XXXV. ELECTROLYSIS . . , :58'. NEW THEOEIES OP MATTEE AND OP FOECE. INTRODUCTORY CHAPTER. THE discovery made by the chemist that all the innu- merable forms of matter with their infinite variety of properties have been built up from a very limited number of substances, the elements, is of comparatively recent date in the long history of science. Although at present no further simplification has been attained, there are not wanting indications that these so- called " elements " are not in a strict sense elementary, but are derivatives one of another, or of some unrecognized simpler forms of matter. Further, some unsuspected and hitherto inexplicable properties of matter, and some obscure relations found subsisting between matter and force, suggest that the dis- covery of the nature of absolutely elemental matter, if it should ever be made, will be found to involve the discovery of the secret of transmutation of energy. In the following pages an endeavour is made to go behind the so-called " elements," and to show that these are really compounds of more elementary substances pos- sessed of certain essential properties. And also, which is still more important, to show that the many different pro- 1 2 NEW THEORIES OF MATTER AND OF FORCE. perties and manifestations of force which distinguish the various more or less complex substances around us, all spring from, and are the direct and inevitable outcome of, these few essential properties of elemental matter ; this latter involving explanations of the correlation subsisting between different physical phenomena, and of the facts which have led to the enunciation of the doctrine of the conservation of energy. Although, in the course of this treatise, the writer will be led to offer an explanation of the facts upon which the conceptions of the modern system of chemistry are based, and to speak of atoms and of molecules, he will found his arguments upon known properties of matter, and will not attempt to go behind these to follow the speculations of molecular-physicists. Thus, while the property of expand- ing in bulk after it has been compressed, so generally exhibited by matter in all its forms, and known as elas- ticity* will be regarded as a universal attribute of matter, no attempt will be made to account for it. And, in speaking of cohesion, no attractive force will be implied ; the supposition very commonly made, that cohesion is the result of attraction between ultimate particles, not being meddled with. To excuse his reticence on points so fundamental, the author would submit First, with regard to elasticity, that he finds all concep- tions of motion, at all capable of accounting for this attri- bute of matter, more difficult and less elementary than the bare conception of elasticity itself ; and further, that he has this difficulty that all material movement and all kinds of strain are in these pages traced to the elastic expansion of a supposed primary matter ; and to deduce another kind of force from elasticity, and at the same time to refer * It will be argued that elasticity of shape may be produced by the combined action of elasticity of bulk and cohesion. INTRODUCTORY CHAPTER. 3 elasticity to this force, would manifestly be to reason in a circle. Further, he might urge that as we really do not know what, in the abstract, space is, and have no means of realizing it except relatively, we have no sufficient reason for accepting the dictum of Lucretius that there could be no motion if atoms fill the universe, " for," says he, " the atoms which give way first must have some empty place to move to." It seems possible to demur to such an assertion, because it is based upon the assumption that a given piece of matter must deducting, of course, all interstices always occupy precisely the same amount of absolute space ; an assumption of which there is no possible proof. Some attributes or properties of matter must be regarded as fundamental ; and why not the attribute of elasticitv, which is perhaps as manifestly universal as any ? Secondly, The author would say with regard to cohe- sion, that the conception of this as merely a holding force, a force of attachment, and not as in any sense a drawing force, will in the sequel appear adequate, in conjunction with our other hypotheses, to account for all the pheno- mena of attraction, and indeed for all action which appears to be action at a sensible distance, however small. The reader's attention is called to the fact that there is an important line of argument in the second chapter of this work which has some application quite apart from the acceptance or rejection of the author's distinctive views as to the constitution of matter. The theory of symmetrical intermixture there offered will explain the spontaneous intermingling of fluids, whether gaseous or liquid, without recourse being had to any unusual hypothesis.* It should be said, in closing these introductory remarks, that while the arguments of this treatise extend to all matter, including that which is manipulated, by life forces, * See page 38. 4 NEW THEORIES OF MATTER AND OF FORCE. whatever these may be, there is no attempt to go beyond the inorganic. Thus no sympathy is here manifested with the tendency to confound forces which, so far as we know at present, are extrinsic to matter, with matter itself, and with forces intrinsic to it ; in other words, to confound life forces, which are not universally present and therefore not intrinsic, and without which the existence of the material universe is perfectly conceivable, with the apparently intrinsic forces, heat, light, electricity, chemical action, crystallization, which are everywhere producible, and seem necessary to the very existence of matter, as we know it. CHAPTER I. FUNDAMENTAL HYPOTHESES. A S a basis for the arguments which are to follow, it is * proposed to set forth (1) A description of what elemental matter is conceived to be. (2) A description of a force of compression conceived to have been applied to this elemental matter, as the result of the application of which it became moulded into the forms of inorganic matter with which we are acquainted. Both these are to be received hypo the tically; no further hypothesis in any sense fundamental will be found requisite in the course of this treatise. The following is the description of elemental matter, which, as will be seen, ascribes to it certain of the recog- nized properties of matter. All matter consists of two elementary substances, which when uncombined, and not subjected to extreme pressure, resemble gases in that they are compressible and elastic, and that as they are freed from pressure their tenuity becomes practically unlimited. They differ from each other in that when, being under the same initial pressure, the same increment of pressure is applied to both, the one has, in all cases, a greater increment of contraction than the other,* and we accordingly * Their behaviour is thus paralleled by that of gases at high density, which are not then obedient to the law of Boyle that the volume of a given mass varies inversely as the pressure. 6 NEW THEORIES OF MATTER AND OF FORCE. designate them this more readily compressible ether and the less readily compressible ether. At some low pressure the density* of the more readily compressible ether is less than that of the less readily compressible ether, and thus a certain pressure is conceiv- able, subjected to which the two ethers have the same densities, and which forms, therefore, a critical point of such a nature that for equal pressures upon the two ethers below it, the less readily compressible ether has the greater density, while for equal pressures above it the more readily compressible ether has the greater density. These elemental ethers are distinguishable from gases by the far greater fineness of their ultimate particles, if the fact of their elasticity requires us to suppose the existence of such, so that for all practical purposes they are to be regarded as homogeneous.f And they also differ from gases in requiring a far greater force of compression to cause them to approach the greatest possible condensation. Some cohesion or stickiness subsists among the ether particles at all densities, both between particles of the same kind and particles of diverse kinds of ether ; the law which regulates the degree of this cohesion being that the total amount of cohesion in any given mass of the same kind of ether is constant^ whatever the density. To put this hypothetic law in algebraic form : If a given mass of ether is in the form of a cube the force necessary to just overcome the cohesion subsisting, say in a plane section taken parallel to one of the faces of the cube, and simultaneously to break away particle from particle through- * For a definition of density, see Note , p. 7. t This will allow us to regard the uncombined ethers as possess- ing a readiness of movement, and facility of penetration of small interstices, far greater than those evinced by gases. t This would seem to involve the conception of ultimate particles of fluctuating magnitude, between which the cohesion to be estimated subsists. FUNDAMENTAL HYPOTHESES. 7 out this section, is constant whatever the magnitude of the cube, and therefore the force necessary to overcome the cohesion in a unit of such a surface, and which force we may take as the unit of the force of cohesion, varies as p, if I be the length of a side of the cube. In the case of cohesion between two different kinds of ether it is supposed that the density of the less dense of the two regulates the law just stated.* The cohesion, which thus increases with increase of density, modifies the expansive force of the ethers, so that as they are more and more highly condensed they manifest less and less force of elastic expansion on release from pressure, till at a sufficiently high condensation they manifest none. Further, in the case of extremest condensation the viscosity of the ethers, i.e., the degree of resistance they oppose to the relative motion of their parts, becomes indefinitely great, so that they reach a perfectly solid state. Finally, the ether particles, like all matter with which we are acquainted, have the property of inertia. It is supposed that the origin of the two ethers just de- scribed, preceded in time the application of any external force affecting them ; and in their primary condition they may be conceived as without motion, or regularity of dis- position in space, and uncompressed. We next come to a description of the hypothetic force conceived to have been applied to the elemental matter, and * Density is supposed to be determined by the quantity of matter present per unit of space. And to enable a comparison between the densities of the two kinds of ether, we may suppose that equal volumes of the different ethers which possess the same amount of internal cohesion contain the same quantity of matter and have the same density. This will suffice to define density with- out reference to gravitation or other properties of the more complex forms of matter. 8 NEW THEORIES OF MATTER AND OF FORCE. which we shall endeavour to show in the following pages would be competent, partly directly, but more largely in- directly, by a legacy of reaction which it left behind it, to mould an inert mass of the ethers we have described into the various forms of inorganic matter with which we are acquainted, and to develop their characteristic properties and forces. This force is conceived to have been simply a force from without, of limited duration, universally applied to compress the primeval ethers, and which gradually diminished their bulk until they had suffered nearly the greatest amount of condensation possible.* This completes the fundamental hypotheses of this treatise. As a preparatory step to building upon these hypotheses a theory of the structure of the " elements," and a number of other theories, we shall in the next chapter deduce a general law of great importance. * Nothing can be known or conceived of the spatial extent of the material universe. Of course if any limits be assigned, the con- densation of hitherto uncompressed matter jnst supposed would involve portions of space being left void of matter. CHAPTER II. THE LAW OF SYMMETRICAL INTERMIXTURE. fTHHE law we thus designate, and whose existence we shall -*- now endeavour to prove, may be stated as follows : If two elastic fluids capable of intermixture, both of which have some viscosity, i.e., oppose some resistance to the relative motion of their parts, and which differ from each other in the amount of compression they experience under the same increments of pressure* are placed in con- tact and subjected to a gradually increasing or gradually decreasing pressure, or to a series of such pressures, they will proceed to intermix wherever their boundaries touch, and a mutual uniform distribution of one fluid throughout the other will take place, of such a nature that both fluids, where intermixture occurs, will tendf to become arranged in small equal masses symmetrically situated in space with respect to one another. And, further, the quantity of matter in each of these small masses will be determined by their degree of condensation at the moment of their pro- duction. The proof of the existence of this law which we have to offer is as follows : For any particular particle of either fluid to continue to occupy the same situation relatively to surrounding particles while a change of pressure is taking place, it is evident that the pressures on opposite sides of it trans- * By hypothesis the two ethers thus differ, f See Note % page 10. 10 NEW THEORIES OF MATTER AND OF FORCE. mitted by these particles must simultaneously change in the same ratio, and thus continue in equilibrium about it. But, unless the two fluids are both symmetrically disposed around the particle, this condition of equilibrium will not subsist ; for, by hypothesis, any change of pressure which takes place produces different degrees of compression in the two fluids, and is therefore unequally transmitted by them. And every change of pressure will, therefore, con- tinually produce some change in the situation of the particle, relatively to other particles, so long as the disposi- tion of these Particles around it is not symmetrical. As this applies to all the particles of both fluids, especially to those in contact with dissimilar particles, we see, therefore, that change of pressure will tend to subdivide and disperse each fluid throughout the other, and to produce a uniform symmetrical mixture of some kind. Now, it is evident that the finer the subdivision of the two fluids caused in this way wherever they come in con- tact, the smaller, on the one hand, the motions of re- arrangement producing it, and the larger, on the other hand, the extent of surface at which the fluids come to touch each other, and throughout which there is friction of one upon the other during change of pressure. Therefore, however little viscosity the two fluids may possess, there will in every case be a certain definite fineness of sub- division producible, depending on the nature of the fluids and the changes of pressure to which they are subjected, beyond which the inequalities of internal pressure occurring are too feeble in their action to overcome the viscosity, and therefore unable to cause any rearrangement of particles. This critical degree of subdivision of the symmetrically intermixing fluids will evidently be that produced in each case ; in other words, as above stated, both fluids will tend* * As for every small mass to have all the other small masses of both fluids symmetrically arranged around it, we should have to THE LAW OF SYMMETRICAL INTERMIXTURE. 11 to become arranged in small equal masses symmetrically situated in space with respect to one another; all less symmetrical dispositions of the two fluids than this being always subjected to change by every change of pressure. It is evident that if different parts of the two fluids experience similar fluctuations of pressure at different times, instead of the pressure being always kept uniform throughout the mass, the above law will still hold. That the quantity of matter in each small mass of either fluid will depend on the degree of expansion subsisting at the time of its ultimate formation is evident. Also that any increase of pressure occurring after a quite symmetrical intermixture has been once produced will not cause any further rearrangement. It is to be observed that when the whole of one fluid has been reduced to small equal masses, and symmetrically distributed among corresponding small masses of the other fluid, there will, unless the two fluids are present in such proportions as to furnish an equal number of small masses of each, be a residuum of one fluid undistributed through- out the other in the symmetrical manner referred to. As to the nature of the symmetrical arrangement pro- duced, we notice that there are but two kinds of disposi- tion of equal infinite numbers of two sorts of similar small bodies in space which are completely symmetrical, and in which each sort is evenly distributed through space, as shown by the property that when the centres of the bodies nearest to any body of the system are joined the solid thus outlined has equal edges. They may be exhibited in the following manner : suppose the matter intermixed to extend infinitely in all directions, less and less symmetry being obtainable as we approach any boundary, it is evident the intermixture will only tend towards the great symmetry referred to, and never completely reach it in any finite case. 12 NEW THEORIES OF MATTER AND OF FORCE. Take a number of equal cubes of two different colours, say black and white, and proceed to build them into a con- tinuous mass in such a manner that no cube shall touch any other cube of the same colour except at its edges, or, in other words, so that a section of the mass parallel to either of the three directions of the faces will present the appearance of a chess board, no square being next to a square of the same colour ; then (1) If, disregarding the distinction of colour, we sup- pose a number of similar bodies of one sort placed with their centres at the centres of all the cubes, and a number of similar bodies of another sort .placed with their centres at all the cube angles, we have an example of one of these systems of symmetrical arrangement. (2) If we suppose a number of similar bodies of one sort placed with their centres at the centres of the black cubes, and a number of similar bodies of another sort placed with their centres at the centres of the white cubes? we have an example of the other system. We submit that the symmetrical arrangement to which the small masses above referred to tend in obedience to the law we have endeavoured to establish will always be that of one or the other of these two systems, in both of which the relative disposition of the bodies of one kind is pre- cisely similar to that of the bodies of the other kind, and the evenness of distribution in space perfect. We may remark in passing, that in adverting to the supposed nature of the symmetrical disposition of small masses of the two fluids, we appear to be treading upon the border land of a most deeply interesting and hitherto little known province of physical law, the formation of crystals ; and may say, as we break off the inquiry into the subject of symmetrical intermixture at this point, that when it is taken up again in the chapter on crystallization, proof will be submitted of the existence of symmetrical THE LAW OF SYMMETRICAL INTERMIXTURE. 13 arrangements of small masses of different kinds of matter of the nature just described. The very wide application of the law of symmetrical intermixture in accounting for a great number of the phenomena of physics, which is shown in the following pages, will afford experimental evidence of its existence. 14 CHAPTER III. THEORY OF MOLECULAR MATTER. THE ELEMENTS. THE task which lies before us in this and subsequent chapters, is to endeavour to show that the experimental facts respecting matter and force can be accounted for by the aid of the foregoing hypotheses, that (1) the various properties exhibited by inorganic matter, in all its forms, are such as certain different combinations of the two ethers, the results of symmetrical intermixture produced by the temporary incidence of the hypothetic force of compression, would display ; and that (2) the various processes, and exhibitions of force, which are taking place in nature, including even those which take place at the bidding of life-forces, whatever these may be, are capable of being regarded as so many different incidents of the gradual return, during countless ages, of these various different combinations of the ethers, to the normal tenuous condition after the removal of the hypothetic force of compression. In the present chapter we shall indicate how the production of a number of ether combinations, which we believe constitute the different simple forms of matter known as the " elements," is conceived to have been a primary result of the temporary subjection of the hypothetic ethers to the hypothetic force ; and, at the same time, we shall point out the probable salient peculiarities * of the different states of these ether combinations, caused by the inter- The identity of these peculiarities with some of the well-known properties of matter is argued in the next chapter. THEORY OF MOLECULAR MATTER. THE ELEMENTS. 15 action of the two kinds of ether composing them on one another. The application of the hypothetic force of compression, and the reaction which, owing to the elasticity of the ethers, would follow the cessation of this force, would, it is argued, through the operation of the law of symmetrical inter- mixture, produce some such different effects as the following, in different parts of the general mass of irregularly dis- tributed ethers, according to the proportions of the two ethers present anywhere, and the particular variations of pressure consequently induced. As the simplest effect we can conceive, if anywhere, as a symmetrical intermixture of the two ethers was completed by the change of pressure, the condensation of both ethers became so great as to give the extremest cohesion of both, there no expansion of either ether would occur on the cessation of the force of compression, and the intermixed mass would present complete stability at a very high density. Proceeding to other conceivable effects, not so simple. Where the high cohesion accompanying the high density did not thus entirely prevent expansion of either ether on the cessation of the force of compression, the expansion of both would take place simultaneously, though with com- parative slowness at first through the restraining influence by hypothesis exerted by the cohesion. But, presently, owing to the different cohesions in the two ethers causing the less dense, i.e., the less readily compressible ether, to expand more vigorously than the other, after some increase of bulk had taken place, the expansion of the small masses of less readily compressible ether of the intermixture would become more violent, while the expansion of the small masses of more readily compressible ether was still inconsiderable. And when this violent expansion of the small masses of 16 NEW THEORIES OF MATTER AND OF FORCE. less readily compressible ether interspersed throughout the mass occurred, if the cohesion of the more readily com- pressible ether were great enough to prevent its disruption,* an effect would evidently follow analogous to that caused by the liberation of minute quantities of gas within a viscous mass, and a cellular condition would be produced, roughly comparable to that of dough, or that of molten lava ; the more readily compressible ether being that flattened out into cell walls, the less readily compressible ether that forming the rounded masses of the cell interiors. Now, for the cells thus formed to enlarge in obedience to the expansion of the ether within them, the superficies of their walls must increase, and for this to occur without any considerable expansion of the highly-condensed ether composing these walls, a continual re-arrangement of the particles must take place, which re-arrangement would be checked by the viscosity of the highly-condensed ether, and we see that on the facility with which the cell walls extend and the cells enlarge depends which of two different results is reached at any particular point. For (1), if anywhere, the growth of expansive force within the cells, occurring as the restraining influence of cohesion diminished, was more rapid than the actual expan- sion allowed by tJie extension of the cell walls ; and so the pressure of the ether of the cell-interiors on the cell walls increased as the mass expanded ; there it is evident the ether of the walls ivould acquire increased density, and expansion would be more and more checked, until the cell walls became so condensed as to be incapable of further extension, and expansion ceased altogether. And wherever this was the case, after some, perhaps slight, general expansion, the mass of mixed ethers would assume a condition of * A glance at the system of cubes of two colours above described shows that each cube is completely enclosed by cubes of the other colour. THEORY OF MOLECULAR MATTER. THE ELEMENTS. 17 great stability, small masses of slightly expanded less readily compressible ether being locked within cell walls of more readily compressible ether so condensed as to resist any effort of the enclosed ether to further extend and thin them out. While, on the other hand (2), if anywhere, the extension of the cell walls was sufficiently rapid to prevent any increase of pressure within the cells from arising through the growing force of expansion of their contained ethers, there, it is evident, expansion would go on indefinitely, unless some external restraint prevented. In this case, however, nearly all the increase of bulk during the earlier part of the expansion would be due to the expansion of the small masses of the less readily compressible ether, the ether of the cell walls continuing in a very highly condensed state, on account of its greater cohesion. And thus, as in the other case, the mass of mixed ethers would present, for a time at least, a cellular structure, the difference being that in the latter case the expansion would be unlimited, unless checked by some external restraint, the cell walls, as the expansion pro- ceeded, becoming extended into very thin films. The magnitudes in masses of ether thus constituted would, of course, be quite infinitesimal, and we have said that the disposition of the ethers would be symmetrical ; but as a rough illustration we may liken the structure produced to a mass of soapsuds ; and this illustration has the advantage that it constitutes a practical proof of the possibility of the force of cohesion holding together a mass of matter arranged in the way last supposed. We may add that the expansion would be far less violent than that of unmixed ethers; in other words, that a far less force of compression would be requisite to continue a mass of ethers thus intermixed than a mass of unmixed etlier of either kind at a degree of condensation 2 18 NEW THEORIES OF MATTER AND OF FORCE. near the greatest possible.* For by hypothesis the con- tinuing high density of the ether of the cell walls would hinder the re-arrangement of their particles necessary for the enlargement of the cells. Indeed the very violence of the expansion would hinder cell enlargement, although it would not prevent it as in the former case. Before suggesting other possible effects it will be con- venient to give some name to the units in the sym- metrically-arranged mixtures above described, which we suppose constitute the simplest forms of molecular matter, and we will therefore call each of the small masses of ether individualized by the law of symmetrical inter- mixture primary atoms ; and this designation will apply to small masses of either ether. Further, we will call each of the minute cells, consisting of the small mass of less readily compressible ether of a single cell interior and so much of the more readily compressible ether of the enclosing cell wall as proportionately pertains to a single cell, a simple primary molecule. The reason for applying these well-known names in this manner is the belief that corresponding units of sym- metrical intermixtures of the different elements produced while they are in a gaseous state form the atoms and molecules of modern chemistry. The ground for this belief is stated in the sequel (see p. 342). To continue our investigation. As another conceivable effect: If anywhere a mass of simple primary molecules, built up, as above described, by a process of symmetrical intermixture, had one kind of primary atoms very greatly expanded, the other extremely condensed, and while in this state, during the continuance of the variation of pressure, came in contact with a mass of the less readily compressible ether, there it is evident a second symmetrical intermixture would commence, small masses of what we * See p. 8. THEORY OF MOLECULAR MATTER. THE ELEMENTS. 19 have supposed to be the simplest form of molecular matter taking the place occupied in the former intermixture by one kind of primary atoms.* The units of mass, or molecules, in such a combination, we will call complex primary molecules. The quantity of ether contained in each of the primary atoms, or small masses, into which the unmolecular ether was broken up by its intermixture with the tenuous molecular matter, would evidently depend on the conditions under which they were produced. Finally, a yet more complex effect may be conceived. If anywhere a mass of such molecules as last described had one kind of atoms only very greatly expanded, and while in this state and during the continuation of the variation of pressure, came in contact with a mass of the less readily compressible ether, or with some other mass of primary molecules of different composition but in a similar state, f there it is evident symmetrical intermixture would again commence, and a mass of still more complex molecules would be produced. The evidence that the elements are certain ether com- pounds, more or less related in constitution to one another, of the nature we have thus indicated, consists in the possibility, we shall in these pages attempt to establish, of framing plausible theories of the various principal pheno- mena of physics based on such a view of the constitution of these simple bodies. Perhaps the most striking parts of this evidence appears in connection with the phenomena of chemical combination and crystallization, the very * We suppose the films separating the highly expanded atoms in the mass of primary molecules to be successively penetrated by the newly separated atoms of less readily compressible ether without permanent rupture, much as the film of an ordinary soap-bubble is sometimes penetrated by other bodies without being destroyed. t A necessary condition is that the two masses of molecules change bulk at different rates under similar changes of pressure. 18 NEW THEORIES OF MATTER AND OF FORCE. near the greatest possible* For by hypothesis the con- tinuing high density of the ether of the cell walls would hinder the re-arrangement of their particles necessary for the enlargement of the cells. Indeed the very violence of the expansion would hinder cell enlargement, although it would not prevent it as in the former case. Before suggesting other possible effects it will be con- venient to give some name to the units in the sym- metrically-arranged mixtures above described, which we suppose constitute the simplest forms of molecular matter, and we will therefore call each of the small masses of ether individualized by the law of symmetrical inter- mixture primary atoms ; and this designation will apply to small masses of either ether. Further, we will call each of the minute cells, consisting of the small mass of less readily compressible ether of a single cell interior and so much of the more readily compressible ether of the enclosing cell wall as proportionately pertains to a single cell, a simple primary molecule. The reason for applying these well-known names in this manner is the belief that corresponding units of sym- metrical intermixtures of the different elements produced while they are in a gaseous state form the atoms and molecules of modern chemistry. The ground for this belief is stated in the sequel (see p. 342). To continue our investigation. As another conceivable effect: If anywhere a mass of simple primary molecules, built up, as above described, by a process of symmetrical intermixture, had one kind of primary atoms very greatly expanded, the other extremely condensed, and while in this state, during the continuance of the variation of pressure, came in contact with a mass of the less readily compressible ether, there it is evident a second symmetrical intermixture would commence, small masses of what we * See p. 8. THEORY OF MOLECULAR MATTER. THE ELEMENTS. 19 have supposed to be the simplest form of molecular matter taking the place occupied in the former intermixture by- one kind of primary atoms.* The units of mass, or molecules, in such a combination, we will call complex primary molecules. The quantity of ether contained in each of the primary atoms, or small masses, into which the unmolecular ether was broken up by its intermixture with the tenuous molecular matter, would evidently depend on the conditions under which they were produced. Finally, a yet more complex effect may be conceived. If anywhere a mass of such molecules as last described had one kind of atoms only very greatly expanded, and while in this state and during the continuation of the variation of pressure, came in contact with a mass of the less readily compressible ether, or with some other mass of primary molecules of different composition but in a similar state, f there it is evident symmetrical intermixture would again commence, and a mass of still more complex molecules would be produced. The evidence that the elements are certain ether com- pounds, more or less related in constitution to one another, of the nature we have thus indicated, consists in the possibility, we shall in these pages attempt to establish, of framing plausible theories of the various principal pheno- mena of physics based on such a view of the constitution of these simple bodies. Perhaps the most striking parts of this evidence appears in connection with the phenomena of chemical combination and crystallization, the very * We suppose the films separating the highly expanded atoms in the mass of primary molecules to be successively penetrated by the newly separated atoms of less readily compressible ether without permanent rupture, much as the film of an ordinary soap-bubble is sometimes penetrated by other bodies without being destroyed. t A necessary condition is that the two masses of molecules change bulk at different rates under similar changes of pressure. 20 NEW THEORIES OF MATTEE AKD OF FORCE. remarkable quantitative and other laws of simple proportion of quantity and of form found to rule these phenomena being hereafter argued to be immediately referrible to just such modes of combination of gaseous elements as those above conceived of the unmolecular ethers. The charac- teristic properties of each element are supposed to be traceable to the particular proportions of the two ethers entering into its composition, and to their structural dis- position. The different states of the ether compounds which have been suggested above we shall, in the next chapter, endeavour to identify with the different states of molecular matter. The magnitudes of primary atoms and molecules must be supposed altogether infinitesimal, for the thickness of the film of a soap bubble, when most attenuated, h;is been calculated to be less than ytinnnF f an inch, and the thinnest film would be composed of more than one, probably of very many layers of molecules. It will appear from subsequent arguments to be a physical im- possibility to make a primary molecule visible by any kind of optical arrangement. As already intimated, the gradual recovery of the two ethers from the effects of the hypothetic pressure is sup- posed to be still going on, and to be the source of all the various merely material phenomena around us ; but while we shall hereafter argue that chemical combination, and other kinds of molecular change, and changes of state are traceable to this source, we regard the manufacture of primary molecules from ethers, in some such manner as that just indicated, as having taken place, once for all, at the time of the imposition, or immediately after the cessation of the hypothetic force of compression. According to the views above propounded, molecular matter is destructible, i.e., convertible into unmolecular ethers. For the failure of its cell wall must, it is evident, THEORY OF MOLECULAR MATTER. THE ELEMENTS. 21 involve the escape of the ether confined in the cell interior of an expanded primary molecule and the consequent de- struction of the molecule, much as the failure of the film of india-rubber of a child's coloured ball involves the escape of the contained gas and the destruction of the ball. As we proceed we shall make the theories of this treatise continually dependent on the supposition that a wholesale destruction of primary molecules, and conse- quent liberation of unmolecular ethers, is taking place. In reply to the evident objection to this that no diminu- tion in quantity of molecular matter is discernible, it is submitted that this may be due to the very great extent to which the ethers are compressed when in the molecular state, and to the infinitesimal size of the atoms, so that an enormous amount of molecule destruction takes place without any perceptible diminution of bulk of the mole- cular matter which is undergoing waste. And as experimental evidence of the adequacy of such an explanation we may instance the case of odorous bodies. For these bodies are moment by moment giving off in- numerable particles, and yet in many cases the amount of waste thus occurring during the lapse of months, in- conceivably great as it must be if estimated by the number of particles, is so insignificant as to elude obser- vation, unless the most delicate instruments are used to ascertain it. Further, the expansion to gas of these in- numerable particles taking place at the surfaces of such bodies, though a change of so violent a nature that when occurring on a large scale it amounts to explosion, pro- duces no perceptible disturbance whatever. Surely if a wholesale waste of particles which have suffi- cient structure to produce a characteristic effect on the organ of smell thus almost eludes observation, it cannot be pronounced intrinsically absurd to suppose that a wholesale waste of primary molecules, in undergoing 22 NEW THEORIES OF MATTER AND OF FORCE. which they lose all structure capable of appealing to any of our senses, may take place without the waste being indicated by any of the tests we are able to employ. It is probable, moreover, that we are not absolutely without evidence of such a waste. For it is found that heating an exhausted tube continuously, or the repeated passage through it of electric currents, improves the vacuum ; and as evidence is brought forward in the sequel that, according to the theories of matter here offered, heat commonly produces atom explosion, i.e., molecule destruc- tion (p. 301), and that so also do electric currents, it is conceivable that the improvement of the vacuum arises from the actual resolution of the molecules of the highly- rarified gas into unmolecular ethers. It is proper to remark, however, that the effect has commonly been attributed to the occlusion of the residual gases by the electrodes. 23 CHAPTER IV. THEORY OF THE DIFFERENT STATES OF MATTER. TT is proposed in the present chapter to point out certain -*- conceivable states of such ether compounds as those whose production we have just traced, which may be supposed to be the various different states of molecular matter familiar to us, and also to indicate the probable nature of the different changes from one state to another. As a preliminary step, however, a short general refer- ence should be made to the means which, according to our 7 & hypotheses, subsist for the production of either change of bulk or change of state of ether compounds ; the detailed consideration of the causes of such changes will be found in the sections of this work devoted to the subjects of heat, of chemical change, and of crystallization. And first as to the contraction of portions of matter of any kind whatever, it should be stated that, avoiding any hypothesis of attraction, we shall in all cases suggest that contraction of matter is due to pressure supplied by the expansion of other matter, a suggestion which may remind us of the modern dictum, that no work can be done without a commensurate expenditure of energy. Next as to what means of expansion are conceivable of the ethers of primary atoms, when their condensation has, as in some of the cases above conceived, become so great as to give the extremest cohesion: It is noticeable in the first place that the conditions at the outer boundary of a mass of highly condensed ethers may not be productive of 24 NEW THE'ORIES OF MATTER AND OF FORCE. the same stability as prevails in the interior of the mass, and changes occurring at the outer boundary may gradually extend into the interior.* Thus if we suppose a mass, which is composed of molecules so highly condensed that the force of cohesion has entirely overcome the tendency to expand, to be surrounded by highly tenuous unmolecular ether, the condition of a particle at a point situated upon its sur- face will be this : If the particle, as a result of its own elasticity, or the elasticity of surrounding particles, makes any movement normal to and away from the surface, there is, according to our theories, no adequate recuperative force to bring it back again, for there are no highly- condensed molecules present outside it, which by their expansion can create for it a force of contraction. It follows that the outermost particles of the mass will expand, and although, by the molecular expansion and destruction thus arising, expansive force will be liberated, by which particles that lie beneath may for the moment continue condensed, the expansion of the outer particles will presently be followed by the expansion of the particles next beneath them ; the expansion of these by the expansion of the particles of the next stratum, and so on continuously ; so that, if time enough be granted, we must anticipate the complete expansion of all the particles composing the given mass. And in the next place, as another means of expansion of such highly-condensed ethers, the bursting of mole- cules, allowing the explosion of their contained atoms, to which allusion has been made, and other changes occurring in molecular matter, must be supposed to produce displace- ments of the ethers and local differences of pressure, and these, through the great elasticity of the ethers and the inertia of their particles, to result in wave motions running * On this see as to Conduction of Heat, p. 316. THEORY OF THE DIFFERENT STAT hither and thither in all directions through both unmole- cular and molecular ethers. Now the vibrations to and fro of the ether particles in waves thus produced would every- where cause local fluctuations of density in the elastic ethers, whether molecular or unmolecular, diminution of density occurring wherever ether expansion takes place, increase of density wherever there is ether condensation.* Therefore we have deduced from our fundamental hypo- theses the existence throughout all matter of an agency productive of the occasional lowering of ether density, and consequently of cohesion. And if anywhere the diminution of cohesion caused by this means is too considerable for the ether condensation which follows ether expansion to neu- tralize, we shall there have a permanent expansion of a portion of the mass.j Let us now see how far we can recognize what are known as the different states of matter in certain different conceivable states of our ether compounds. * Upon the principles of this treatise we have therefore to dis- criminate between the mean general pressure within a gas or a liquid and the fluctuating local pressures which are determined by the passage of wave-vibrations. To take a simple example : suppose we have an open vessel containing atmospheric air at the normal atmo- spheric density. We are accustomed to regard the whole of such a bulk of air as subject to a constant pressure, the weight of the atmosphere, but if we accept the conclusions of this treatise it is evident that, since we must regard it as traversed by such waves of sound as may happen from time to time to be passing, if we fix our attention upon some particular particle of the air it is not strictly correct to say that this particle is subject to a constant pressure, and is therefore at a constant density ; for the sound- vibrations in which it participates will produce fluctuations of pressure, the values of which must be distinguished from the value of the mean general pressure which is unaffected by them. + Very symmetrical waves of ether, some of which are manifested by the light, others by the heat they produce, it will be contended in the sequel are active agents in causing atom-expansion andatoiu- explosion in the interior of masses of matter. 26 NEW THEORIES OF MATTER AND OF FORCE. It is commonly stated that there are three distinct states of matter, namely, the solid state, the liquid state, and the state of gas or vapour ; and these broad distinctions gene- rally suffice for all practical purposes. If, however, our fundamental hypotheses are to be admitted, we must add a fourth to these three states, namely, the ethereal state. In addition to this, the course of subsequent argument will, on many grounds, be found to justify the splitting up of one of the three recognized states into two, distinguishing a cellular solid state from a non-cellular solid state. We then have five states of matter broadly distinguish- able from each other, viz. : 1. The non-cellular solid state. 2. The cellular solid state, 3. The liquid state. 4. The gaseous state. 5. The ethereal state. Of these five states, the first four we suppose are mole- cular, in the sense attached to this word in this treatise, and the fifth unmolecular ; the broad difference between a molecular and an unmolecular state of matter being, accord- ing to the views which have been submitted, that molecular matter is a symmetrical intermixture of the two ethers in which either there is no expansive force because of the great density of all the ethers present, or the force of expan- sion of one ether compresses the other into highly-condensed septa or films whose cohesion restrains this force. Un- molecular matter, on the other hand, is either unmixed ether or an intermixture in which no portions of matter are continuing permanently condensed. Taking the different states of matter in the order just given, we suppose : 1. That the non-cellular solid state is the state presented by any mass of intermixed ethers composed of any number of different sorts of primary atoms which have reached the THEORY OF THE DIFFERENT STATES OF MATTER. 27 condition of great stability referred to in the last chapter, in which the atoms of both kinds of ether are so condensed that they manifest no expansive force, except in the fitful way next stated. Throughout every mass of matter in this state, and in- deed throughout all ma.sses of molecular matter, in whatever state, local temporary fallings off in density and cohesion, occasioned as above explained, or otherwise, are, we sup- pose, continually here and there producing the expansion of small portions of molecular matter to the unmolecular or ethereal state. If, as we have said, the expansion of molecular matter is always either prevented or restrained by the cohesion of its denser portions, it is evident the expansive force of ethers let loose in this way within a molecular mass will, as the particles of the mass become rearranged by passing waves, cause these ethers to percolate through the molecular matter to find a vent ; the facility with which they accomplish this being greater as their degree of continuity is greater, and as the breaks made in this continuity caused by any dis- turbing motions in the mass are less. Every mass of molecular matter will in this way have complete porosity for the passage through it of unmolecular ethers. Again, the degree of tenuity attained by unmolecular ethers which are thus percolating through molecular masses will evidently be limited by the facility with which they pass away ; and we suppose that owing to their passage being hindered by the action of one unmolecular ether on the other (see p. 17), their density, although much less than when they were in the molecular condition, is to some extent proportionate to the density of the atoms from which they are evolved. By hypothesis any keeping up of density involves a keeping down of expansive force. For the non-cellular solid state to continue unchanged the quantity of unmolecular ethers produced by molecule 28 NEW THEORIES OF MATTER AND OF FORCE. destruction within a mass in this state as just supposed must, it is evident, bear a quite infinitesimal proportion to the quantity of condensed ethers composing the molecular matter. Unlike the cellular states of molecular matter that have bsen described, in which the cohesion of the ether of some atoms prevents or restrains the expansion of other atoms, this highly condensed state is evidently one in which no great internal strain exists. It will appear probable from subsequent considerations that it is perfectly exemplified only by some few of the metals. 2. We suppose that the cellular solid state is the state presented by a mass composed of any number of different sorts of primary atoms in which one or more kinds of atoms are not so condensed as to prevent their expansion, and the expansive force of these atoms has compressed some or all the other kinds of atoms into septa or cell walls of such a density that their cohesion altogether prevents their expansion and makes them able to bear without spreading or breaking the pressure of the partly expanded atoms which they enclose. We referred to this state in the last chapter (see the first of the two cellular states described, p. 16). The application to all matter in this state of our general supposition that unmolecular ethers are being liberated throughout all molecular matter, and percolating through it, in this way bringing about its complete porosity for un- molecular ethers, must not be overlooked. As in the case of the other solid state it is evident that, for the state to con- tinue unchanged, the quantity of these ethers evolved must be very limited indeed. We shall argue as we proceed that most solid bodies indicate by their properties that they furnish examples of this state. THEORY OF THE DIFFERENT STATES OF MATTER. 29 3. As to the liquid state. It is well known that this state, in the case of some substances, and, indeed, in the case of all more or less, passes so insensibly into the solid state that no line of demarcation can be fixed. Thus before it reaches fluidity iron loses its hardness, and becomes soft, so that pieces may be welded together or moulded into various forms, and some substances, which behave entirely as fluids if sufficient time be given them, have the appearance and properties of solids, on account of their great viscosity, e.g., cold tar and asphalte. And in this way properties which appear at first sight to pertain exclusively to liquids are found, to a limited extent, to belong also to solids ; while some properties of solids are found to characterize all liquids. We suppose the liquid state to be the state of a mass of different kinds of primary atoms, whose general expan- sion is prevented by cohesion in one or the other of the two ways we have just described, when suggesting the nature of the two solid states, but in which the quantity of unmole- cular ethers liberated, as above supposed, is too great to allow of different parts of the mass rigidly retaining the same relative situation as they do in the solid state a state, there- fore, in which the mass may be regarded as consisting of a number of small masses of molecular matter in one of the solid states already described, whose continuous contact with one another is prevented by the frequent liberation from their surfaces and passage between them of unmolecular ethers which as they are liberated pass away. We suppose 4. That the gaseous state is the state presented by a mass of intermixed primary atoms of different kinds in which the considerable expansion of some of the atoms while the rest remain very condensed has produced a cellular condition of the mass in the manner described in 30 NEW THEORIES OF MATTER AND OF FORCE. the last chapter (p. 17), the pressure exerted l>y the ether of the cell interiors, and consequently the density of the cell walls and their viscosity diminishing as the expansion pro- ceeds, so that the cells continually enlarge, and the mass as a whole expands, unless prevented by some external pressure. The fluidity of the gaseous, like the fluidity of the liquid state, we attribute to the continual liberation of unmolecular ethers throughout the mass, these ethers percolating through the molecular matter as above sug- gested. All gases, we know, are found to have some viscosity, i.e., they oppose a resistance to the relative motion of their parts. 5. The ethereal or unmolecular state was defined above. We suppose that matter in this state is never met with by us in any considerable quantity separate from molecular matter, and that what there is of it around us is distributed among small masses of molecular matter. Some of the phenomena of light, of heat, of electricity, of magnetism, and of chemical change will be argued to be due to its presence and its movements. Next, as to the probable nature of the different changes from one to another of the above states. Transition from the non-cellular solid to the liquid state we suppose to be due to an increase in the quantity of un- molecular ethers being liberated in small quantities within bodies in the former state the viscosity, or adhesion of the small masses of the bodies to one another becoming less and less as this increase takes place : Heat will, in the sequel, be argued to be a principal cause of increase in quantity of the unmolecular ether being liberated within a body. The liquefaction of bodies which are in the cellular- solid state we suppose to be a very similar change, but that some complication arises from the effect of the increased THEORY OF THE DIFFERENT STATES OF MATTER. 31 liberation of unmolecular ethers on the conditions of in- ternal strain and cellular structure which we have supposed are present in this solid state. The fact that many solids, which we shall hereafter see reason to believe are in the cellular-solid state, particularly crystals, diminish in bulk on liquefaction, leads us to suppose that the effect referred to is the production by local temporary accessions of pres- sure, resulting from the increased ether liberation, of sufficient condensation of the slightly-expanded ether of some, at least, of the cells to make this ether lose its expansive force, so that it continues condensed, and does not press upon the other ether enclosing it. For if, as suggested, the liberated ethers rapidly escape from the interstices of the molecular matter of the mass, such a state of things would evidently cause a diminution of bulk. Before we refer to the converse of this last change, and the other changes of state which remain to be treated, an important conclusion as to local fluctuations of pressure, and consequently of density and cohesion, should be stated. We have argued the existence of waves which traverse all kinds of matter, and produce local fluctuations of den- sity, and consequently of cohesion. And we have concluded that, if anywhere the diminution of cohesion caused by this means is too considerable for the ether condensation which follows ether expansion to neutralize, we shall there have a permanent expansion of a portion of the mass.* If, therefore, here and there throughout a mass which is in one of the highly-condensed states, small portions are permanently expanding through the action of passing waves, it will be at points where the local cohesion, when at the ebb of a wave it approaches a minimum, falls below a critical value, at which it ceases to be high enough to prevent the existence of expansive force in the ethers of *See page 25. 32 NEW THEORIES OF MATTER AND OF FORCE. the mass, no permanent expansion taking place where the minimum cohesion continues above this critical value.* In harmony with this, we suppose, in reference to the transition from the liquid to the cellular-solid state, that the very extreme condensation of some atoms arising from the expansion of others, which we have supposed to be the characteristic feature of the latter state ; in other words, the cellular condition of this state, is produced with more or less suddenness as the conditions of the crystallizing liquid change in such a way as to lower the minima values of the cohesion of the atoms whose expansion produces the cellu- lar condition past a certain critical value, depending on the substance employed. f The facts that the change is sudden in many instances, and that it is commonly accompanied by a sudden increase of bulk, are, it is suggested, to be accounted for in this way. This theory explains the fact that some liquids, when nearly at the point of sudden transition to the solid state e.g., water near the freezing point are caused to solidify by lowering the external pressure upon them while other conditions remain unchanged. J For it is evident that a diminution of the external pressure upon a liquid will lower all the local pressures within it which are fluctuating be- tween maxima and minima at the bidding of passing waves, and will thus make the minima values of pressure and of cohesion lower than before ; and if, therefore, the minima values of cohesion of the atoms whose expansion produces the cellular-solid state are at the outset just above the critical value above referred to, the diminution of external * The amount of change produced will thus, it is evident, largely depend on the amplitude of the waves. t An explanation of the probable cause of the lowering of these minima is given in the sequel, p. 302. I As a converse phenomenon. Moresson succeeded in lowering the freezing point of water to - 18 C., by the application of a pressure of 13,000 atmospheres. THEORY OF THE DIFFERENT STATES OF MATTER. 33 pressure will, if considerable enough, carry them past this critical value and produce a change of state. In cases where the passage from the liquid to the cellular- solid state is marked by diminution "of bulk, e.g., in those of paraffin and spermaceti (which we suppose furnish examples of the latter state), we may suppose that slight expansion of some atoms is overbalanced by a shrinkage of bulk, due partly to the drawing closer together of the atoms generally, as the quantity of unmolecular ethers liberated within the mass diminishes, partly to the compression of the atoms not expanding. And such a theory would explain the fact that bodies which display this property of con- tracting on congelation, have their melting points raised by pressure, e.g., spermaceti melts at between 50 and 60, under a pressure of 156 atmospheres, being 3 higher than its normal point of solution. For we should expect increase of the pressure upon a body to diminish the quantity of unmolecular ethers being liberated within it, and since, according to our theories, it is increase of the quantity liberated which causes liquefaction, increase of pressure would in diminishing the quantity of ethers liber- ated, defer change of state, or, in other words, raise the melting point in the scale of temperature. As to the transition from the liquid to the gaseous state, we suppose that the cohesion at all points of a mass in the former state being, as above explained, kept fluctuating in value by passing waves, the change referred to is brought about by the lowering of the minima values* of the fluctu- ating cohesion of those atoms whose expansion produces * We may call attention here to what it is suggested is a familiar example of the existence of points of minimum cohesion in a liquid . If a glass of soda water or other aerated water is observed as the effervescence is subsiding, it is seen that the minute bubbles of gas passing out from the liquid are moving in regular files at equal distances with almost soldier-like precision. The explanation suggested is that where a bubble is formed, the 3 36 NEW THEORIES OF MATTER AND OF FORCE. of the effects of change of state, may be adequately ex- plained according to the theories which have been offered. Take a glass globe of given capacity, provided with a stop-cock, a pressure-gauge, and a thermometer. Intro- duce into this globe a small quantity of water, and then, closing the stop-cock, expose it to the temperature of boiling water. If sufficient water have been provided, it is seen that the given temperature is adequate to vaporize a certain quantity of water, and no more ; so that any excess beyond this continues as a liquid at the bottom of the globe.* Next, without allowing any of the contents of the globe to escape, and still preserving the same given temperature, introduce through the stop-cock a small quantity of liquid alcohol ; it immediately begins to vaporize, and continues to do so until, as in the case of the water, a point is reached at which all the remaining alcohol continues liquid. Further, on investigation, the remarkable fact is revealed that the globe holds almost as much vapour of alcohol as though no vapour of water were present. Finally, retaining, as before, all the previous con ton ts and preserving the same temperature, in a similar manner, introduce a third liquid ether. Again an expansion takes place, a certain quantity of the ether gradually evaporates, till with this also a limit is reached beyond which all the residue continues liquid ; and, as was the case with the alcohol-vapour so now with the ether-vapour, the capacity of the globe for ether-vapour is found to have been almost as great as though no other vapour had been present. The general mean pressure exerted by the combination * This fact is an instance of the law first formulated by Dalton, that, in a space destitute of air, the vaporization of a liquid goes on only until the vapour has attained a determinate pressure de- pendent on the temperature, so that, in every space void of air, which is saturated with vapour, determinate vapour-pressure corre- sponds to determinate temperature (see p. 305). THEORY OF THE DIFFERENT STATES OF MATTER. 37 of vapours upon the sides of the vessel is found to ap- proximate to the sum of the pressures which the three vapours would severally exercise, under the given con- ditions, if present alone. The explanation of these phenomena appears to be as follows: The fact already explained that the boiling point of a liquid is lowered in the scale of temperature by a fall of external pressure, raised by a rise of external pressure, will evidently account for the successive forcing up of the boiling points of the three liquids past the given constant temperature by the pressure afforded by their confined vapours. The remarkable facts that the presence of the aqueous vapour does not appreciably diminish the capacity of the vessel for the alcohol-vapour, and that the presence of both the steam and the alcohol- vapour does not appreciably diminish its capacity for the ether-vapour, we should interpret as showing that a general or mean pressure, exerted by a less volatile gas or vapour, does not appre- ciably affect the position of the minima of the local density and cohesion of the atoms of a more volatile gas with which the less volatile gas is mixed. The reason of this, we surmise, is that the existence of different rates of expansion and contraction of different kinds of atoms produces dissonance of pulsation, so to speak, when these atoms participate in wave motions, and prevents continuous communication of pressure from one kind of atom to another; and that this allows an occa- sional lapse of the density and cohesion of the atoms of one kind to minima values little or no higher than would be presented if the pressure caused by the presence of atoms of other kinds were removed altogether. The con- ception is, however, somewhat difficult. It has been stated as a fundamental hypothesis respect- 38 NEW THEORIES OF MATTER AND OF FORCE. ing the two ethers that, under a change of external pressure, the one will expand or contract, as the case may be, more than the other. It is, however, a matter of experience that gases, which we have argued are various intermixtures of the two ethers, have a sensibly constant, and therefore similar, rate of expansion through a wide range of changing pressure. This fact is expressed by what is known as the law of Boyle or Marriotte : That, provided the temperature remains the same, the volume which a gas occupies is inversely proportional to the pressure subsisting upon it ; or, in other words, its density is proportional to its pressure. It is evident that, if our conclusions be correct, such a law as this can be but approximately true, and this only between certain limits of density. It would not prove true for a state of very high condensation. And on the other hand, its application to a state of unlimited tenuity would imply the possibility of absolutely unlimited expan- sion. It is found experimentally to be but an approximate law, Regnault having shown that air and all gases, except nydrogen, have co-efficients of dilatation which increase to some extent with their density. The accuracy of Boyle's law increases, however, under conditions of increasing tenuity, a fact which is embodied in a second law of Regnault, that the co-efficients of dilatation of the different gases approach more nearly to equality as their pressures become feeble. The important phenomena of the spontaneous mixing of gases and the diffusion of liquids may evidently be attri- buted to the action of the law of symmetrical intermixture, the changes of pressure requisite to bring the law into operation being those caused by passing waves, as above explained.* * The intermixture of gases is referred to again, p. 339. 39 CHAPTER Y. THEORIES OF GRAVITATION AND CAPILLARY ACTION. A MONGr the fundamental hypotheses of this treatise, 4^? no hypothesis of action at a distance is laid down. The reason is, that in all those cases where a body acts on another body without contact with it, and without the intervention of any apparent material connection, we shall find that we are able to argue that the effect is due to certain motions and dispositions of the hypothetic ethers incidental to their gradual recovery from the condensation produced by the hypothetic force. In the present chapter we shall offer theories, reached by this line of reasoning, of the forces of attraction always found present in connection with all kinds of molecular matter, and known as gravitation* and * It is interesting to notice that, if we succeed in accounting for the force of attraction known as gravitation on first principles, with- out having recourse to the notion of action at a distance, we shall be realizing an expectation of the great Newton, the hold of which on his mind is indicated by the following passage, taken from a letter written by him to Bentley : " It is inconceivable that inanimate brute matter should, without the mediation of something else which is not material, operate upon and affect other matter without mutual contact, as it must do if gravitation in the sense of Epicurus be essential and inherent in it. . . . That gravity should be innate, inherent, and essential to matter, so that one body can act upon another at a distance, through a vacuum, without the mediation of anything else, by and through which their action and force may be conveyed from one to another, is to me so great an absurdity, that I believe no man, who has in philosophical matters a com- petent faculty of thinking, can ever fall into it." 40 -NEW TmiOZtfES OF MATTEK AND OF FORCE. capillary action: Magnetic and electrical attraction and repulsion, which, as far as their manifestation in any appreciable degree is concerned, are forces peculiar to par- ticular bodies, or to particular conditions of bodies, will be dealt with subsequently. The following general proposition, based upon our funda- mental hypotheses, and upon the conclusions from them which we have arrived at above, contains, it is submitted, the principle lying at the root both of gravitation and of capillary attraction. If, in a molecular body, the conditions are such that the un- molecular ethers which are present within it, as above supposed (see p. 27), have their density continuously greater in any given direction, the body will, as the result of the wave motions everywhere traversing matter (see p. 24), tend to move in this direction ; i.e., in the direction in which the most rapid increase of density of the unmolecular ethers is found. The proof of this proposition which we have to offer is as follows : According to the above theories, all molecular matter, even that in the gaseous state, is restrained by the cohesion of its denser portions from the freedom of movement we have attributed to the unmolecular ethers, and, therefore, the molecular framework of any given body will not par- ticipate fully in wave movements or other motions under- taken by the unmolecular ethers occupying its interstices ; just as in a sponge, filled with water, small motions of the water are not fully participated in by the matter of the sponge. Consequently the molecular surfaces within the body, at which the molecular matter is in contact with the contained unmolecular ethers, will continually experience the passage past them, in various directions, of the un- molecular ethers, as the latter make small local wave movements* or other motions. * See p. 24. THEORIES OF GRAVITATION AND n ATfrg^&ff V m*Eyifr 41 But, by hypothesis, some degree of cohesion or adhesion subsists between the molecular surfaces within the body and the unmolecular ethers which thus pass and repass them continually, and therefore, each time a small motion takes place of the unmolecular ether in contact with any portion of molecular surface, the molecular matter will ex- perience a force tending to move it in the direction taken by the ether. Where the ether movements are of the nature of waves of some kind, the force experienced at any point tending to move the molecular matter in a particular direction, will generally, it is evident, be succeeded by a force acting in the opposite direction ; but it is not necessary, or indeed possible, to suppose such opposite forces in every case equal, and we conclude that, as the result of the numberless small forces thus applied by the fluctuating ethers at all points of the molecular surfaces within the body, a slight degree of displacement of the body as a whole, in some direction or other relatively to the general mass of un- molecular ethers permeating it, will continually be taking place. Now, and this is the keystone of our argument, the amount of displacement thus from time to time taking place, depends, not only on the nature and extent of the ether motions which produce it, but also on the amount of cohesion or adhesion subsisting between the molecular surfaces and the unmolecular ethers which pass them; for this de- termines how far an ether motion of given extent shall be communicated to the molecular matter. In other words, the amount of displacement depends on the density of the unmolecular ethers, since, by one of our hypotheses, cohesion is regulated by density. Therefore, a small displacement due to a certain series of ether movements will be a maximum when it occurs in the direction of greatest density of the unmolecular ethers. 42 NEW THEORIES OF MATTER AND OF FORCE. And, finally, it follows from this that as ether m tions must be supposed to take place equally, on the average, in all directions, their effect on a molecular mass will be greatest in the direction in which the ether density is greatest, and the resultant displacement, with respect to the general mass of unmolecular ethers, will have this direction. Our proposition is therefore established. To establish the probability that both gravitation and capillary attraction are examples of the displacement of molecular masses with respect to the unmolecular ethers they contain, thus brought about that they are the off- spring of the drag of the minute ether surges on the mole- cular matter past which they play we shall argue the existence of conditions of graduated ether density in the case of each of these forces, such as, according to the above proposition, would account for the precise phenomena observed. First, as to the existence of gradation of density of the unmolecular ethers adequate to produce gravitation. We have supposed that every detached molecular mass is liberating unmolecular ethers which pass away on all sides, and if, as we have concluded from the supposed constitution of molecular matter (p. 27), all molecular masses have complete porosity for the passage through them of unmole- cular ethers, the radiations of unmolecular ethers, thus taking place, will communicate their motions both through space destitute of molecular matter, and through the inter- stices of the molecular masses they encounter* Now, whether the moving ethers are passing through space void of molecular matter, or traversing the interstices of the mass from which the radiation is taking place, or those of some other molecular mass, it is evident that, * We have supposed that the unmolecular ethers within mole- cular masses maintain a high density as compared with ether in space destitute of molecular matter (see p. 27). THEORIES OF GRAVITATION AND CAPILLARY ACTION. 43 owing to their elasticity of bulk, their density will con- tinually diminish as their distance from the centre of radiation increases. And, therefore, as an effect of the supposed ether liberation, we have a falling gradient of density of the unmolecular ethers, outward from the molecular mass from which radiation is taking place, i.e., in the direction in which, according to the above proposition, the gradient should fall, to account for a force of attraction towards this molecular mass. In answer to the evident objection that the continual motion of translation of the unmolecular ethers which are thus furnishing a gradient of ether density will produce a force of repulsion so far as the molecular surfaces in contact with the unmolecular ethers partake of this motion of translation, it is urged that the amount of the ether motions occurring in passing waves may be far greater than the amount of the ether motions of translation ; so much greater, indeed, that the force of repulsion due to the latter may be altogether inappreciable compared with the force of attraction which results from the former.* With reference to the remarkable law discovered by Newton, that the force of attraction exerted by a body on another body varies inversely as the square of the distance : If our theory is sound that the attraction of gravitation is the result of the cohesion or adhesion subsisting between the molecular surfaces in the interior of bodies and the unmolecular ethers in contact with these surfaces, and we suppose that in cases where the law of Newton holds the repulsive force due to the motion of translation of these ethers is inappreciable and accordingly neglect it, it would evidently appear from the existence of Newton's law that * There is some evidence of repulsion by the sun of bodies coming into near proximity to it. 44 NEW THEORIES OF MATTER AND OF FORCE. where various detached bodies are exerting mutual attrac- tions of gravitation, the degree of cohesion or adhesion subsisting at different points between the internal molecu- lar surfaces of one of them and the unmolecular ethers in contact with these surfaces follows the law of Newton, i.e., is in the ratio of the resultants of the various forces of gravitation, emanating from all the detached bodies exerted at these different points respectively.* Now, according to one of our fundamental hypotheses, for the cohesion of the unmolecular ethers throughout a unit of surface to vary as w the density of these ethers must vary as 73, and therefore we conclude that the sub- sistence of the relation between the values of the cohesion at different points, just argued, indicates that the density conditions of the unmolecular ethers prevalent at any place are the result of concurrent ether radiations from the various centres of attraction such as would, if each were taking place alone, respectively give the ether density! in the inverse ratio of the cube of the distance from the centre of radiation. :{ To speak more explicitly, it indicates that the gradation of density of the unmolecular ethers present in each mass, and which, according to our theory, is the source of the movement of this mass which actually occurs, is, both as to direction and gradient, the resultant obtained by the composition of gradations of ether density * In stating this we, of course, leave out of account any change in the relative positions of the detached bodies occurring from time to time, and treat them as fixed bodies. f We have concluded that at all points the ether density is fluctuating in value owing to the passage of waves of alternating compression and expansion, and therefore what is meant here is that the average ether density varies according to the law stated. J This relation would evidently involve the velocity at which the ethers travel varying directly as the distance from the centre of radiation. THEORIES OF GRAVITATION AND CAPILLARY ACTION. 45 which would respectively be produced in this mass if ether radiation from each of the various attracting centres, follow- ing the law just referred to, took place by itself. * Towards accounting for the kind of radiation of the unmolecular ethers which we have thus argued must obtain for the law discovered by Newton to exist, we have to offer the following : It is reasonable to conclude that any radiating ethers will, on account of their viscosity, move unitedly in such a manner as to produce the least possible amount of re- arrangement of their particles. When they are traversing space destitute of molecular matter, and supposing radiation to take place from one centre only, this requirement will manifestly be met, indeed the ether expansion will take place without any re-arrange- ment of particles whatever, if all the linear dimensions of every small mass of ether radiated varies as its distance from the centre of radiation, i.e., if, in other words, the density of the ethers varies as the inverse cube of the distance from this centre. When radiating ethers are traversing the interstices of molecular matter, frequent re-arrangement of some of their particles will, it is evident, take place, and, when radiation takes place from more than one centre, ether accumulation must occur at some places and produce some degree of modi- fication ; but the argument that the ethers will move unitedly in such a manner as to produce the least possible amount of re-arrangement of their particles will nevertheless still apply, and we shall therefore be justified in expecting that whatever ether motions take place they will very approxi- mately be in conformity with the law just referred to. * It is easy to see that if this is so the paths of the moving ether particles will, if produced, meet in a point, and that the resultant gradation of density, just referred to, will follow the law of inverse cubes with reference to this point as centre. 46 NEW THEORIES OF MATTER AND OF FORCE. Such is the theory we offer of the origin of such gradients of ether density as would account for the force of gravitation varying inversely as the square of the distance. Some significant facts may be mentioned in connection with the theory of gravitation which has been submitted above. Messrs. G. H. Darwin and H. Darwin have made some refined experiments, showing that a freely-hung pendulum, however carefully protected from disturbing causes, is in a state of continual oscillation, and this although the instrument used was found practically insensible to the effect of local tremors. They have also found that such a pendulum is subject to a diurnal oscillation, and to a gradual change of the mean diurnal position. Again, M. Plantamour has called attention to what appears to be a periodic rise and fall of the ground in Switzerland, which he regards as associated with changes of temperature of the earth's surface. And, finally, Prof. Naudin has recently observed a lowering of the level of the Mediterranean at Antibes (Alpes Mari times) which amounts to 30 centimetres. He believes its cause to be volcanic, but Dr. Faye, of Paris, connects it with high atmospheric pressure. It is suggested that a probable explanation of these and of other similar facts is, that slight changes in the force of gravitation are produced by the occurrence from time to time of slight departures from uniformity in the ether liberation to which we have attributed the production of a gradation of ether density. To account for the diurnal changes referred to, we suppose that the ether liberation of the earth is affected by the position of the sun, whose power of causing ether liberation will be referred to hereafter. Next we may mention the important fact that, in different localities, the direction of gravitation manifests various different aberrations from the strictly vertical. THEOKIES OF GRAVITATION AND CAPILLARY ACTION. 47 The received theory that the force of gravitation resides in each particle of the substance of the earth, and that the amount of attractive force emanating from different points is proportional to the density at such points, has naturally led to an endeavour to explain these local aberrations of the direction of gravitation by the outline of the earth, or by the distribution of the different substances of various densities which compose it. Thus, it has been customary to refer any local aberration from the vertical, that is, from the line through the earth's centre, found in the direction of gravitation to the force of attraction of some neighbouring mountain or elevation of the earth's surface ; and if no mountain was present, and the nature of the ground surface gave no encouragement to such an expla- nation or appeared to contradict it, then refuge has been taken in the supposition that the arrangement of masses of greater or less density beneath the earths surface is such as to produce the observed variation. The theory of gravitation which has been propounded points to an entirely different explanation. We are not concerned with the general outline of the earth's surface in the locality under consideration, or the disposition of rocks of different densities, but with the nature of the ether liberation in this locality ; for on this, we suppose, depends the direction of the steepest gradient of ether density, and consequently the direction of gravitation. Probably the direction of the steepest gradient of ether density at any point will be affected by the relative proportions of the two ethers evolved around this point; an aberration from the vertical being produced if the proportions of the two ethers being evolved on one side are very different from the proportions evolved on the opposite side. And if this is so, it seems probable that the proportions of the two ethers evolved from water on the one hand, and from rocks and soils on the other, differ 48 NEW THEORIES OF MATTER AND OF FORCE. considerably, for we find that the most marked aberrations of the direction of gravitation are commonly found at localities near the sea. To mention an example: At a very exceptional station on the north coast of Banffshire, near the village of Portsoy, the deflection amounts to as much as 10", and there are no adequate surface conditions of the undulating country near to account for any such aberration, upon the basis of the common assumption above alluded to. Some pendulum observations made in India are in harmony with these views. Thus the mass of rocks constituting the Himalaya mountains is not found to produce the deflection which their bulk would, according to the customary theory above referred to, lead us to expect ; so that it has actually been stated as proved that the density of the strata of the earth's crust under and in the vicinity of these mountains is less than that under the plains to the south. Interesting facts have been by the same observations brought to light with regard to the relative variations of gravity at continental, coast, and island stations, it being found that, without a single exception, gravity at the coast stations is greater than at the corresponding conti- nental stations, and greater at island stations than at coast stations.* It is not, however, intended to convey that the configu- ration of the land has no effect on local attraction ; it is simply suggested that its only effect consists in any modi- fication it produces of the direction of the steepest gradient of ether density. The fact that the amount of movement of a body caused by gravitation is, as our theory would lead us to expect, independent of the density of the body, is well shown by the familiar experiment of simultaneously letting fall a * " Encyclopedia Britannica," Art., " Fig. of the Earth." THEORIES OF GRAVITATION AND CAPILLARY ACTION. 49 sovereign and a feather in vacuo, when it is found that the two different bodies fall in the same time. Finally, we may refer to the fact of very different densities having been deduced for the various heavenly bodies upon the received theory that the attractive force they exercise resides in their particles, and depends on their respective masses ; e.g., the density of Jupiter is calculated to be about one-fourth that of the earth. As the above theory, instead of making the attraction depend on the mass of the attracting body, makes it depend on the amount of radiation of unmolecular ethers, pro- ceeding from this body, no such differences of density of the heavenly bodies need be supposed, according to this theory r , and we thus escape the difficulty of reconciling the existence of such differences with the modern discovery of the similarity of constitution of so many of the heavenly As to the connection between weight and gravitation. According to the above theory the weight of a body will, it is manifest, be expressed by the number of units of molecular surface there are within it, a unit of molecular surface being the extent of surface which has unit cohesion with the unmolecular ethers. The number of such units in any particular body will, it is evident, vary according to the density of the unmolecular ethers within it. In accordance with this the weight of a body depends on its distance from the earth or other attracting body. Capillary Action. Capillary action takes its name from the behaviour of water or other mobile fluid in a very small tube, so small as to be comparable in internal calibre to the size of a hair. It is found that when such a tube open at both ends is lowered endways into water, the water rises within the tube to a higher level than the water outside. 4 50 NEW THEORIES OF MATTER AND OF FORCE. The existence at the surfaces of bodies of a gradation of density of the unmolecular ethers adequate, according to the general proposition submitted at the commencement of this chapter, to account for the phenomenon of capillary attraction, follows at once from our supposition (p. 27) that the density of the unmolecular ethers present within molecular masses is to some extent proportionate to the density of the atoms composing these masses. For, if such is the case, then, wherever a dense body is surrounded by a vacuum, or by a medium whose density is not so great as its own, there will be a sudden fall of density of the unmolecular ethers from the interior of the body, across its bounding surfaces, into the medium outside it, and we shall have along all such surfaces a steep gradient of falling density of these ethers extending from some, probably very short, distance within the body to some, probably very short, distance outside it.* And, as supporting this, we may cite the discovery made by Quincke, that for several series of substances the capillary force at the surface is nearly proportional to the density. The following, based on the theory of capillary attrac- tion thus completed, is our explanation of the rounding off of what would otherwise be the angles and edges of the free surfaces of liquids, and the softening of their outlines ; phenomena which, since the middle of the last century, have been attributed to a surface-tension, because the contours presented are such as can be produced by a uniform stretched membrane. We have argued that forces of displacement of molecular matter caused by gradations of density of the unmolecular ethers always follow the directions in which the most * It may be mentioned that Poisson maintained that there is a rapid variation of the density near the surface of a liquid, and that this conclusion has since received confirmation. THEORIES OF GRAVITATION AND CAPILLARY ACTION. 51 rapid increases of density of these ethers are found, and it follows from this that such forces everywhere act per- pendicular to surfaces throughout which equal density of the unraolecular ethers prevails ; consequently, every small portion of the free surfaces of any liquid mass will be found coinciding as nearly as the subsisting conditions of the matter of the mass generally will allow, with some such surface of uniform ether density. But since the density of the unmolecular ethers at any point on the boundary of a molecular mass will depend on the conditions of ether density prevalent for some distance around this point, it is evident that the value of this density at such a boundary will, where the structure of each of the molecular masses meeting at this boundary is uniform, vary according to the contour of the surface around the place of observation. Thus, on a projecting portion of the mass, this value will be relatively lower if the ether density within the mass is higher than the ether density outside it, relatively higher if the contrary is the case ; and, on the other hand, in a depression of the general surface, this value will be relatively higher if the ether density within the mass is higher than that outside it, relatively lower if the contrary is the case, and therefore in the case of a mass of liquid, bounded by a free surface, this surface will not be in equilibrium, and will consequently experience change so long as it has not a certain definite form which gives the density of the unmolecular ethers as uniform as possible throughout every small portion of it. The nature of the surface in which equilibrium is thus reached will evidently depend on the ether conditions pre- valent in the liquid, and in the medium outside it, and also on any modifying effects produced by gravitation, the presence of solid boundaries, or other causes. In the case of a mass of liquid, surrounded on all sides by some uniform fluid, and free from any external modify- 52 NEW THEORIES OF MATTER AND OF FORCE. ing conditions, equilibrium will be reached only when the bounding surface becomes spherical. In harmony with this conclusion we have the following familiar fact : When any falling mass of liquid has broken up into fragments, owing to its particles not being capable of re- arrangement with sufficient rapidity to allow the continual elongation of the mass by the action of gravitation to proceed without rupture, the fragments, after a series of oscillations of form, settle down to a spherical shape. We may also refer to an experiment of M. Plateau with two liquids of the same specific gravity. After forming a mixture of alcohol and water of the same specific gravity as olive oil, he introduces a quantity of the oil into the mixture, when, if no modifying conditions are present, the mass of oil suspended within the mixture assumes a spherical form. Here we argue from the fact of the two liquids, the oil and the mixture of alcohol and water, not diffusing into each other that their respective particles at any place where they touch do not interlock as the result of the motions which, according to the previous arguments, they are continually making, so that there is wJiere they meet a narrow space but little intruded upon by the dense matter of the liquids. For, if the particles of different kinds did to any considerable extent come into close contact, we con- clude that diffusion would take place through the operation of the law of symmetrical intermixture (p. 38). Now, if there is at the boundary between the two liquids this narrow space comparatively clear of molecular matter, a double gradation of density of the unmolecular ethers will, according to the above theory of capillary attraction, subsist, i.e., a falling gradient of density from each liquid into this intervening space, and the explanation given above will apply, and the spherical form taken by the mass THEORIES OF GRAVITATION AND CAPILLARY ACTION. 53 of oil be attributable to the surface of each liquid finding equilibrium in this form. * Next we will call attention to one or two examples of the application of the above explanation to cases where a mass of liquid has its general form modified by gravitation, and contact with more than one kind of substance. Thus the following is the explanation submitted of the familiar fact that a drop of one liquid placed upon the surface of another liquid in many cases e.g., in the case of a drop of melted fat placed upon water assumes the form of a lens, and does not spread itself over the surface in a film of growing tenuity as its attraction to this surface seeks to make it do, and as is seen in some other cases. The force of capillary attraction present near the surface of the one liquid, which tends to spread out the drop of the other liquid placed upon it, is on the one hand rein- forced by the gravitation of the drop, and on the other hand opposed by the endeavour of the drop to take a spherical form, caused, as above explained, by the capillary force at its surface. The resultant force thus subsisting, which acts primarily on the particles of the drop lying within range of the capillary action of the liquid surface on which it rests, * An experiment made by M. Duprez brings out the resistance to change of form subsisting at a surface between two liquids which do not diffuse into one another. He places a vessel containing olive oil with its mouth downwards in a vessel containing a mixture of alcohol and water, the mixture being denser than the oil. The surface of separation is in this case horizontal and stable, so that the equilibrium is established of itself. Alcohol is then added very gradually to the mixture till it becomes lighter than the oil. The equilibrium of the fluids would now be unstable if it were not for the resistance referred to, and which, when the orifice of the vessel is not too large, continues to preserve the stability of the equilibrium. When the equilibrium at last becomes unstable, the destruction of equilibrium takes place by the lighter fluid ascending in one part of the orifice and the heavier descending in the other. 54 NEW THEORIES OF MATTER AND OF FORCE. and tends to spread the drop, willj it is evident, begin to fall in value as the drop spreads slightly when first placed upon the surface ; for the effect of gravitation, which aids in spreading the drop, will diminish as the vertical height diminishes, and at the same time the capillary force acting on the surface of the drop, which opposes its spread, will increase as its form departs more and more from the spherical. Now this diminishing resultant force is resisted by the viscosity of the liquid composing the drop, and it is suggested that in the cases under consideration, when the drop has spread to a certain limited extent, this resultant is thereby brought down to a critical value at which it is just too small to overcome the viscosity, i.e., the resistance of the liquid to the relative motion of its parts, and so no further spread of the drop takes place. When this state of equilibrium is reached, and we have taken into account the displacement by the drop of a portion of the liquid upon which it floats, the extent of which will depend on the comparative specific gravities of the two liquids, we may evidently conclude that at every point in some surface intersecting the lower portion of the drop, throughout which the resultant force of displacement is a maximum, this force has the critical value just referred to, the general distribution of tJie matter forming the drop being in this way determined. Finally, the precise curvature of surface presented in such cases is evidently referrible to the capillary force at this surface ; this force, according to the above argument, producing such a form as will give the density of the uninolecular ethers as uniform as possible, consistently with the above, throughout every small portion of surface. In harmony with the above conclusion, that the general distribution of the matter forming the drop, that indeed its continuance as a drop, is determined in any given case by THEORIES OF GRAVITATION AND CAPILLARY ACTION. 55 the viscosity, we have the fact observed by Andrews that the capillary action becomes weaker as the temperature rises, and vanishes at the critical point at which the distinction between the liquid and its vapour ceases. In proof that the capillary force seeking to spread the drop depends on the kind of molecular matter present within a very thin stratum at the surface on which it floats, we have the interesting fact that when a drop of train oil placed upon a large body of water has spread out into a film of infinitesimal thickness, i.e., when so thin that it ceases to produce interference colours, its presence causes a second drop placed on the surface to remain gathered up in a lens shape with a distinct circular edge. The same line of argument as we have just offered will apply to the familiar phenomenon of a liquid remaining in equilibrium though its surface stands slightly above the edge of the vessel containing it. Also to the case of a o O drop placed upon a solid surface. It should be observed, in connection with the latter case, however, that where the density of the un molecular ethers within the drop is very great, the value of this density at and just below its surface will be almost as great where the liquid adjoins the air as where it adjoins the solid, and the capillary attraction exercised by the solid will consequently be small. It is suggested that this is why small drops of mercury placed on most solids take a nearly spherical form, the capillary action at the surface of the mercury having almost nothing but the gravitation of the liquid metal to oppose it. The familiar fact that with most liquids the free surface where the liquid meets the side of a vessel which rises above it, curves upward, so that at its edge the liquid stands rather higher than elsewhere, is explained as follows : We suppose that where this is the case the density of the unmolecular ethers present within the substance of the 56 NEW THEORIES OF MATTER AND OF FORCE. vessel is greater than the density of those within the liquid. The consequence of this will be that at, and just below, the general surface of the liquid which lies against the side of the vessel, the ether density will be higher than it is at the free surface ; and, therefore, that surfaces of uniform ether density lying at and just below the general free surface of the liquid will not extend in the same plane up to the sur- face of the vessel, but will turn upwards near to it. And, consequently, if it were not for the falling off in ether den- sity, which we have concluded exists in any projections of a mass (p. 51), thin films of liquid projecting upwards from the general surface next the sides of the vessel would have the ether density within them as great as that subsist- ing at and immediately beneath the general free surface of the liquid, and would therefore be in equilibrium. That in the cases under consideration the liquid merely curves upward slightly at its edge, and does not form these thin films, we attribute then to the form of the surface, where the liquid projects upward at its edge, causing the density of the unmolecular ethers to be lower in the project- ing portion ; the combined result of the capillary action of the surface of the vessel, and that of the surface of the liquid, being that the surface of uniform density of the un- molecular ethers, which coincides with the general free surface of the liquid, after passing upwards a little near the edge, turns and passes down again to join the surface of the same density lying parallel to the side of the vessel a short distance within the liquid. The curvature of the liquid surface will, as before, be such as gives the density of the unmolecular ethers as uni- form as possible throughout any small portion of this surface. The rise of a liquid in a capillary tube, of which the accompanying diagram represents an exaggerated section, we refer to the effect of a high density of the un- molecular ethers within the liquid near the surfaces of the THEORIES OF GRAVITATION AND CAPILLARY ACTION. 57 1. tube, produced as above, in giving a relatively higher ether density within the tube at the level of the general surface. For the consequence of this will be that for the surface of the liquid to follow a surface of uniform ether density, it will have within the tube to stand at a height above the general level such that the height- ening of the ether density just re- ferred to shall be just counterbalanced by the weakening of this density due to the projection beyond the general surface (see p. 51). The explanations given of the previous case will apply to account for the precise forms taken by the surface. That when a glass tube is dipped into a vessel of mercury, the mercury within the tube stands at a lower level than outside, would be similarly explained, if we suppose the density of the unmolecular ethers within the substance of the glass to be less than that of those within the mer- cury. For if this is so, the intrusion of the glass will lower the ether density within the mercury close to the glass, and, for a surface of uniform ether density to be followed by the liquid surface as before, a depression of the portion of the latter within the tube must occur such as to give a strengthening of the ether density at this part of the surface (see p. 51) just sufficient to counter- balance the weakening due to the intrusion of the glass. As an instance of the mutual effect of the capillary forces at the surfaces of two different liquids in contact in effecting change of form, we may refer to the fact that if a drop of alcohol be made to touch one side of a drop of oil on a glass plate, before equilibrium is reached under the capillary conditions thus produced, a considerable motion of the boundary between the two liquids in the direction from the alcohol to the oil takes place. 58 NEW THEORIES OF MATTER AND OF FOECE. A similar effect is observed if a drop of water and a drop of bisulphide of carbon are placed in contact in a horizontal capillary tube, motion taking place in the direction from the bisulphide of carbon to the water. To refer next to cases of changes of form of liquid masses where the capillary action emanating from solids with which they are in contact preponderates over the capillary action emanating from the liquids themselves : When a drop of water is introduced between two glass plates nearl}' in contact, slightly inclined to each other, it thins itself out as much as possible by running towards that part where the glass plates are nearest together, although, as we know, a drop of water in contact with a single glass surface does not become thinned out in this way. By way of explanation of this we observe that the fact of all the small portion of free surface present in this case having its ether density modified by the near proximity of the glass would cause the capillary force at this surface, which tends to prevent extension of the drop, to be very small, and thus would account for the pre- ponderance of the spreading force exercised by the capillary attraction of the glass surfaces. The enormous force pro- duced by the introduction of a drop of water in this way, which presses the plates together so powerfully as often to bruise certain parts of them, or to break them, is probably due to the close proximity of the surfaces of the two plates bringing all the water present between them to within an infinitesimal distance of the solid surfaces, and thus con- fining it to the place of steepest ether gradation and greatest capillary attraction ; and to small continuous por- tions of the molecular matter of the liquid* consequently experiencing at different parts of them at the same time powerful capillary attractions to both the opposing surfaces. The instance of capillary action furnished by the familiar * See p. 29 as to the supposed constitution of a liquid. THEORIES OF GRAVITATION AND CAPILLARY ACTION. 59 occurrence of a towel drawing the water out of a basin into which it dips will have a similar explanation to the above experiment with two glass plates. * The phenomenon called the " tears of strong wine " may be mentioned in this connection. When a glass is partly filled with strong wine the liquid creeps up the side, and collecting into drops runs down again, and these drops are found to be more watery than the rest of the liquid. The explanation suggested is that the capillary force at the surface of the strong wine is inadequate to prevent the spreading effect of the capillary action emanating from the glass, so that a thin film of the liquid rises up the sides ; that, as the alcohol in this thin film evaporates more rapidly than the water, the capillary force emanating from the liquid of the film increases, so that presently it is sufficient to overcome the capillary force emanating from the solid on which it rests, and begins to collect the liquid of the film in distinct patches of greater thick- ness ; and, finally, that this clears the greater part of the glass surface and allows further quantities of the strong wine to be drawn up ; the quantity of watery liquid growing from time to time, as the process goes on, into drops of sufficient magnitude to run down by gravitation. The attraction of a floating body towards the edge of a liquid in cases where the edge curves upward, and the converse repulsion from the edge in cases where it rounds downwards, will both, it is evident, be referred to the pro- duction of different gradations of density of the unmolecular ethers, on opposite sides of the floating body, caused by the influence above explained of the form of the molecular surface of the liquid on surfaces of uniform ether density * It is needless to say that for the towel to form a syphon, and let the water drop from the outer end, this end must be lower than the surface of the water, so that the weight of water in the portion of the towel outside may be sufficient to overcome the weight of that in the portion inside. 60 NEW THEORIES OF MATTER AND OF FORCE. drawn at the boundaries of the floating body and the liquid on which it rests. As different liquids will have different gradations of density of the unmolecular ethers at their surfaces, we should expect that when masses of two kinds of liquid contained in the same vessel have their free surfaces adjoining, a surface of uniform density, drawn at the surface of the general mass, will have irregularities, trending slightly up- wards or downwards where it passes from one material to the other. And this appears to be the explanation of the fact that when a drop of alcohol is placed on the surface of water the equilibrium of the surface is changed in such a way that if the depth of the water is only two or three millimetres the surface current produced sweeps away the whole of the water, leaving a dry spot where the alcohol was dropped in. It will similarly explain the fact that if a drop of ether is held near the surface of water, the vapour of ether condensing on this surface produces surface currents flow- ing in every direction away from under the drop of ether. It would appear to be owing to the effect just alluded to that if a small body floating in a shallow vessel of water has one side wetted with alcohol or ether, it moves off with great velocity, and skims about on the surface of the water with the alcohol at the stern. Before we leave the subject of capillary action, a fact generally regarded as furnishing evidence of the existence of a surface-tension of liquids demands explanation at our hands: Liquid films whose surfaces are free, i.e., in contact with gases, are found to have a tendency to contract. M. Dupre has described an arrangement by which this is illustrated.* A rectangular frame formed of sheet metal, three sides * Leidenfrost showed in 1756 that such a contraction occurs in the case of a soap bubble, the bubble diminishing in size if the tube with which it is blown be left open. THEORIES OF GRAVITATION AND CAPILLARY ACTION. 61 of which are continuous, and the fourth, a very fine strip, movable, is dipped into a solution of soap, or of M. Plateau's glycerine mixture, so that the space within the rectangle may become covered by a liquid film. It is then found that contraction of the film is occurring tending to slide the movable side of the rectangle upon the two sides adjacent to it. The explanation we have to offer is as follows : First, as to the formation of the film. As the frame is being lifted from the liquid the liquid runs off from it by the law of gravitation, aided at last by the capillary attrac- tion found at the surfaces of the liquid ; but since the effect of these forces on the mass varies as its bulk, while the cohesion varies as its section, a point is presently reached when a continuous mass of liquid remains within the rect- angle, the forces acting on which are insufficient to over- come the cohesion which links particle to particle, and the outside particles to the frame, and thus we have a thin film adhering to the sides of the rectangle. The time this film will last depends largely on its rate of evaporation ; if the evaporation is very rapid the film will be immediately destroyed. Next, as to the contraction of the film. The very perfect regularity of the surfaces of the film is evidently accounted for by its not finding equilibrium under the capillary action at these surfaces, until the form they take gives the density of the unmolecular ethers as uniform as possible throughout every small portion of surface (see p. 51). As, however, a number of local impulses are continually being imparted to the film by the wave motions and other small motions occurring in the gases in contact with it, and also in the unmolecular ethers found among its molecules, we must suppose that local temporary distortions of the film which elude observation are continually taking place. 62 NEW THEORIES OF MATTER AND OF FORCE. Now, the capillary force just alluded to must, it is evident, as it acts on small temporary elevations or depres- sions of either surface, produce slight local fluctuations in the substance of the film, temporarily thickening and tem- porarily thinning it here and there. If it were not for the evaporation of the film which, to a greater or less extent, is proceeding, it does not appear that local fluctuations of thickness thus produced would have any but a local and temporary effect, but since, as above suggested, the thickness of the film at the time of its formation is the result of a limit being reached, at which the cohesion of the particles suffices to resist the forces seeking to re-arrange them, we see that motions which thin the film will experience more resistance than motions which thicken it, and that the net result of the local changes of sub- stance, just referred to above, will be to thicken, and conse- quently to contract it. The process of thinning the film by evaporation will consequently be somewhat retarded. The very small distance from a surface to which any appreciable gradation of ether density, capable of producing capillary attraction, extends, is indicated by the observa- tions of Quincke and others, who find that the extreme distance at which an effect is produced is from a thousandth to a twenty-thousandth part of a millimetre. A reference to change of form of capillary surfaces produced by the presence of electricity, confirmatory of the above theories, will be found in the sequel (p. 123). ELECTRICITY. CHAPTER VI. THEORY OF WHAT ELECTRICITY IS CONDUCTION. THAMILIAR as the phenomena of electricity have be- *- come to us all, the question, " What is electricity?" has hitherto remained unanswered. To some extent the same ignorance may be said to prevail of the two yet more familiar handmaids of matter, light and heat, but not altogether, for while no fundamental theory of electricity which has obtained at all general acceptance, has yet been offered, the latter are partially accounted for by accepted theories, more or less satisfactory. As to all the three exhibitions of force, light, heat, and electricity, that they have an intimate relation to matter in all its forms, is evident, for they all may, by appropriate means, be evolved from all known kinds of matter ; but they are generally rather regarded as in their origin external to it, or as imparted to it, and not as necessarily inhering in all matter. We shall endeavour to show in this treatise that light, heat, and electricity are all, considered apart from the impression which they make on our senses (which im- pression is a function of our organization), strictly inherent in matter, the outcome of the fundamental properties we have ascribed to it ; that they are, in fact, motions, or changes of relative position made by the different masses ,... 64 NEW THEORY OF ELECTRICITY. of ether, of which, according to our hypotheses, matter consists, as they seek equilibrium. The vehicle of communication of all three from place to place, we shall consequently argue, is found in the unmolecular ethers, and all their manifestations will be referred to the effects of the presence and movements of the un- molecular ethers on the above described molecular matter.* Electricity is, it is suggested, the condition of molecular matter which is brought about by contact with a body of one kind of ether present alone ; positive or vitreous electri- fication resulting from the presence of one of the two ethers (which we shall therefore call positive ether), nega- tive or resinous electrification resulting from the presence of the other ether (which we shall therefore call negative ether).} We shall now proceed to test the plausibility of this supposition, by showing how far it is consistent with and explanatory of many of the very various phenomena of electricity. CONDUCTION AND NON-CONDUCTION. The almost instantaneous communication of electrical effects from one point in space to another, e.g., the passage * An important part has been already assigned to the unmolecular ethers, in producing changes of bulk and changes of state ; and these changes can, we know, in most cases, be referred to the action of light, heat, or electricity generally to the action of heat. t Dufay, more than a century ago, first discovered the existence of two kinds of electricity ; and Symmer, in the last century, maintained the theory of two distinct fluids, not independent of each other, but coexistent, and, by counteracting each other, produc- ing all the phenomena of electricity. For a familiar means of distinguishing positive electricity from negative electricity, see p. 79. Some reasons will be subsequently given for believing that positive electrification is due to the presence of an excess of the more readily compressible ether; negative electri- fication to that of an excess of the less readily compressible ether. CONDUCTION AND NON-CONDUCTION. of an electric current through thousands of miles of metal wire in a few minutes, is perhaps, to the casual observer, the most astounding of all the electrical properties, and is so contrary in its aspects to our usual ideas of the motions of matter, that although an electric "fluid" is commonly spoken of, it is not usual to regard it as a substance. The difficulty of supposing it to be a substance is however, to some extent, obviated, if we regard the con- ductor as a reservoir already filled with electric fluid. For in this case we need not consider the almost instant- aneous transmission of the effect from one extremity to the other to be evidence that matter which was present at the one end has all, or any part of it, actually passed to the other end, since it is no more necessary to suppose that the same electric fluid which flows in at the one end flows out at the other, than to suppose that, when more water is added to that within a receptacle already full, the overflowing drops are those, and those only, which are added. We have already supposed that molecular matter in all the states in which it is presented to us is permeated by un- molecular ethers (see p. 27), that it is in fact, to some extent, a reservoir of unmolecular ethers,* these ethers preserving a density in some degree proportionate to the density of the atoms among which they are evolved. And, in harmony with this supposition, the explanation of conduction which we have to offer is, That ether of each sort, contained in and around the molecular matter of a conductor, is found capable of displacement by a stream of similar^ ether, just as water in a pipe is displaceable by water poured in at one extremity * Upon this supposition the foregoing theories of gravitation and, capillary action are based. t The reason for supposing that only the similar ether is thus, displaced is given immediately. 5 66 NEW THEORY OF ELECTRICITY. of the pipe, and that, taking into account the incomparably greater mobility of unmolecular ether than of molecular liquid, a continuous stream of water trickling down the underside of some solid body may be regarded as the analogue of an electric current in a conducting wire ; the motions of the fluid being in both cases due to the transmitted pressures being out of equilibrium.* In thus explaining electrical conduction, there is one difficulty to be met, which has no doubt already occurred to the reader. If both ethers are present among the molecules of the conductor, why should not the entrance of a body of one ether at one extremity of the conductor displace both ethers equally, and produce a current at the further extremity, not of the same ether only, but of both ethers mixed as they occur in the conductor ? The reply to this important objection is based upon the hypothesis that the two ethers expand at different rates, and is as follows : If conduction is of the nature just suggested there must in a conducting body be a continuous chain of ether particles simultaneously displaceable in the direction of the current. Now, the local fluctuations of density due to passing waves, which we have argued that all matter, xin whatever state, is continually undergoing (p. 25), will, since by hypothesis one ether is more readily compressible than the other, continually alter the arrangement of the particles of one ether relatively to the particles of the * The capillary action of a piece of string, when it empties the water from a vessel into which it dips, will furnish a still better illustration. It may be mentioned that the passage of an electric current, caused by disturbance of electrical equilibrium, has often been compared to the flowing of water from a higher to a lower level, e.g., in the case when, on an electrified ball being placed in con- tact with a precisely equal and similar unelectrified ball, the charge becomes equally divided between the balls. CONDUCTION AND NON-CONDUCTION. 67 other, but they will not materially alter the relative ar- rangement of the particles in any given mass composed of one kind of ether only except at its boundaries, where it is in contact with the other ether. And therefore the trans- mission of pressure through a mass of ethers will en- counter a perpetual succession of checks in seeking to pass from one ether to the other, and be indefinitely retarded, but will take place instantaneously through con- siderable distances where one ether only is present. Consequently, where ether pressure applied at one end of a conductor finds a continuous mass of one ether un- mixed with the other, it will be transmitted almost entirely through this mass, and not to any perceptible extent through any mixed ethers which are also present.* To account for the presence of continuous chains of particles of each ether unmixed with particles of the other ether in conducting bodies, such as this explanation pre- supposes, notwithstanding the existence of the law of symmetrical intermixture, we suggest that in all bodies small masses of intermixed unmolecular ethers are con- tinually here and there temporarily separated into their constituents by the disturbances to which we suppose all matter to be continually subjected, and that the com- position of conducting bodies is such that re-intermixture does not take place so readily in these bodies as in non- conductors ; and, further, that minute imperceptible ether currents are everywhere continuously traversing all con- ducting bodies, whether they are apparently electrified or not. Of the latter supposition some evidence will be submitted subsequently. * We shall argue presently that, so far from the entrance of one kind of ether at one extremity of a conductor producing a flow of the other kind of ether out from the other end, the flow of one ether in one direction in a conductor invariably produces a flow of the other ether in the opposite direction as a consequence of the law of symmetrical intermixture (see p. 75). NEW THEORY OF ELECTRICITY. The above suggestion, that unbroken continuity of one ether upon the surface or within the interstices of the conducting body is indispensable to good conduction, receives some experimental confirmation. Thus we have the fact that more force is requisite to start a current than to maintain it, Varley having found, in passing an electric current through a Geissler's tube, that it required 323 cells to start the current, but that to maintain it 308 cells were adequate. And this, in terms of the above theory, indicates that the flow of a stream of ether between two points is facilitated by a favourable disposition of the ethers between these points.* We have, too, a fact pointing in the same direction, which is analogous to the fact that different portions of a stream of water, owing to their experiencing different retardation by friction, move at different rates. In a very long conductor, a long submarine wire for instance, a short, sharp signal sent in at one end comes out at the other as a signal gradually increasing from nothing to a maximum, and then gradually dying away. And this evidently indicates that the electrical condition of the wire is gradually produced, and also that this condition con- tinues with a gradually diminishing intensity for a short time after the producing cause has ceased to act. Further, we may cite the elementary fact that positive and negative electricity tend to neutralize each other, so that if a conductor receives two charges of electricity of equalf quantity but opposite sign it exhibits no trace of electricity whatever. For we may suppose that sym- metrical intermixture of the two ethers occurring, as already argued, when they come together (see p. 9), each * A striking confirmation of this is found in the necessity of a condition of preparedness of the voltaic arc, referred to in the sequel (see p. 196). t We ought, perhaps, rather to say " commensurate." CONDUCTION AND NON-CONDUCTION. 69 ether, when the intermixture has taken place, continually breaks the continuity of the other as passing ether waves cause them to expand or contract at di/erent rates, and that each ether in this way prevents the motion of the other, except so far as the insensible ether motions above referred to are concerned. From this it would follow that it is the difference and not the sum of the two ethers present at one spot which ordinarily determines the amount of electric force ex- hibited.* Finally, as furnishing corroborative evidence of the above suggestion, we may refer to the facts as to the various degrees of conductivity found in matter in different states and of different kinds. Thus, if unbroken continuity of one ether is essential to good conduction, we should expect those bodies in which there is least molecular vibration or disturbance to be the best conductors, those in which there is most the worst. Now, in the case of most of the elements, the solid state is characterized by the highest conductivity, the liquid state by the next highest, and the gaseous state by the lowest ;f and according to our theories as to the nature of these states, which theories are supported by the respective characteristics of the states, the amount of intermolecular motion they severally have follows just the inverse order, i.e., there is least motion in the non-cellular solid state, considerably more in the liquid state, most of all in the gaseous state. * We shall endeavour to show hereafter that the effect of the intermixed unmolecular ethers on molecular matter with which they come in contact belongs to another branch of physics ; that it is a phenomenon of heat and not of electricity (see p. 302). f The relative conductivity of metals is generally considered to be determined by the relative amount of resistance which they exhibit to an electric current (see p. 151). 70 NEW THEORY OF ELECTRICITY. And again, Bodies which from their optical* and other properties we shall see reason hereafter to conclude are in the cellular solid state, are bad conductors. And this is explained, if we suppose that the ready transmission of ether waves, which we shall argue characterizes substances in this state (p. 269), is attributable to the readiness with which the cellular mass moves in obedience to wave motions which traverse it, and that the vigorous wave vibrations transmitted through matter in this state produce rupture of continuity in each ether permeating it. It seems likely, however, that when, as in most cases, such bodies are chemical compounds, it is to want of unison in the pulsations of small masses of different elements which lie next one another, f arising through their different com- pressibility, that rupture of continuity of the unmolecular ethers is chiefly due. Of the substances we suppose to be in the cellular solid state which are bad conductors, we may mention shellac, jet, glass, diamond, silk, wool, feathers, marble, chalk and lime. Most chemical compounds, when fused or in solution, show rather rapidly increasing conductivity with increase of temperature. On the other hand, the conductivity of metallic conductors would appear to diminish, but more slowly as the temperature rises (see p. 303). The explanations given above apply to differences in surface conductivity. Thus, we suggest that the reason why electricity will not pass along the surface of polished glass as readily as along the surface of polished metal, is that the surface of the glass, as well as its entire substance, is in such a state of continual minute vibration that ether- * See p. 272. t Chemical compounds are hereafter argued to be symmetrical intermixtures of infinitesimal equal masses, or secondary atoms of different elements. CONDUCTION AND NON-CONDUCTION. 71 continuity of each ether in the body of dense unmolecular ethers coating the surface* is perpetually broken. As we should expect if the cause of non-conduction is that suggested, the efficacy of a non-conducting body or insulator is increased by diminishing its perimeter and increasing its length ; for example, a long fibre of glass or raw silk is an excellent insulator. Since our arguments trace the insulating power of a body to broken continuity of each of the ethers within it, produced by molecular motions, it does not surprise us to find that although ordinary air is a good insulator, highly rarefied air is a conductor, that in fact while increased pressure increases dielectric strength, diminished pressure decreases it. For it is reasonable to expect that as the molecules of the gas become more expanded and less numerous, they will have less power by their vibrations to break the continuity of currents of unmixed ether seeking to traverse the gas. As to the important fact that a limit to the operation of this law is presently reached, so that when special means are employed to render the vacuum as nearly perfect as possible, the resistance increases so much as to prevent any observable discharge, we may hazard the suggestion that discharge is not prevented, as at first appears, but that the current which passes is almost infini- tesimal in quantity because the ether which it displaces has extreme tenuity. The reason that the track of the discharge becomes at last invisible or non-luminous, we suppose to be that the amount of molecule destruction is inconsiderable when the quantity of molecular matter present has become infinitesi- mal, molecule destruction, i.e., atom explosion, being in the sequel supposed to be the producing cause of the waves which propagate light. The fact that very hot air is a conductor will appear * See p. 50. 72 NEW THEORY OF ELECTRICITY. explicable when in the sequel we trace the presence of heat to the exhibition of a large quantity of the unmole- cular ethers (see p. 302). That negative charges are generally dissipated, without a parent conduction, more readily than positive charges, is perhaps due to the same waves producing less motion in one ether than the other, so that under the same condi- tions ether continuity is more broken in one ether than in the other. 73 CHAPTER VII. ELECTRICS AND NON-ELECTRICS. ELECTRICITY LIBERATED BY MOTIONS OF MOLECULAR MASSES. THE TWO ETHERS MOVE IN OPPOSITE DIRECTIONS. TT is a matter of experience that patches of electricity *- may lie upon a surface of glass, or of some other non- conductor, without travelling away by conduction, and this produces the distinction between electrics and non- electrics, for while it is well established that electricity can be developed by the friction of any substance, it is ordinarily obtainable from non-conducting substances only because it passes away insensibly, as it is generated, when it is developed by, friction of a conducting body.* A very suggestive experiment first devised by Lichten- berg seems to show that different substances are, in their normal condition, undergoing molecular disintegration, and emitting some an excess of one, others an excess of the other kind of ether, and at the same time throws light on the nature of deposits of positive and negative ethers upon a non-conducting surface. If the knob of a charged Leyden jar is drawn over the surface of a plate of shellac or vulcanite, the outside coating * In a communication to the Royal Society of Edinburgh, in Jan., 1879, James Blyth, M.A., F.R.S.E., showed that electric currents were produced by the mere friction between conducting substances. The passing away of electricity from a conducting body, when the body is not insulated, is simply an instance of the property displayed by electricity of distributing itself at the. external boundary of a conductor, or system of connected conductors, to which reference is made presently (see p. 88). 74 NEW THEORY OF ELECTRICITY. being connected with the earth, patches of positive electri- city are deposited upon the surface. If on the other hand the outside coating is drawn over such a surface, while the inner coating is connected with the earth,* patches of negative electricity are similarly deposited. And when a mixed powder, consisting of flowers of sulphur and red lead, is afterwards shaken upon the plate, the sulphur adheres to those parts of the surface upon which positive electricity is deposited, and the red lead to those upon which negative is deposited, the result being very striking, the branching lines of the positive deposits and the circular spots of the negative deposits revealing very marked difference in the behaviour of the two electricities. The suggested explanation is that the sulphur is emitting an excess of negative ether, the red lead an excess of posi- tive, and that a selective action of the two different ethers upon these two substances arises in consequence, according to the well-known laws of attraction, between diverse electricities.! Our supposition, that atoms are composed of the two ethers, which is thus countenanced, is also supported by the facts that electrification is caused by pressure, by cleavage, and by rupture ; for if we suppose these agencies to pro- duce atom explosion, we shall, according to the composition of the atoms exploded, look for the presence of an excess of one ether or the other among the undestroyed atoms. J We will next offer an explanation of the fact that elec- tricity is producible in very considerable quantities by friction. The first step towards this is the establishment of the * When the operator changes his hold upon the jar from the out- side coating to the knob, he must, of course, place it upon an insulating stand. t These laws will be investigated presently. Further evidence in the same direction is furnished by the facts of voltaic electricity. THE "LAW OF OPPOSITE CURRENTS." 75 following important theorem, which will be subsequently referred to as the law of opposite currents. If masses of the two ethers are present, unmixed, in con- tact with each other, the passage of one ether in a particular direction directly operates to produce the movement of the other ether in the opposite direction. The proof, which immediately depends on our conclusion that the motion of one ether has no appreciable effect in producing motion of the other ether in the same direction, coupled with the law of symmetrical intermixture, is as follows : As the result of the law of symmetrical intermixture, if masses of the two different ethers are side by side, each will pass towards and inter-penetrate the other ; in other words, they will pass in opposite directions. But the ethers which do not directly intermix, are, by cohesion, attached to, and therefore carried along with, those which do, and since, as we have argued, the fluctuations everywhere occurring which produce intermixture, do not materially alter the relative arrangement of the particles within any small mass composed of one ether only, but do continually alter the arrangement of the particles of one ether relatively to the particles of the other, each ether engaged in the act of intermixing will carry with it ether of the same kind, which, for the moment, remains un- intermixed, in preference to ether of the other kind. And therefore, in all cases where masses of the two ethers are present, unmixed, in contact with each other, the two ethers will move in opposite directions, both those which are in the act of intermixing, and those which are not, and the law just stated is established.* To apply this law to the subject under consideration the production of electricity by friction. * The fact of the flow of the two electricities in opposite directions 76 NEW THEORY OF ELECTRICITY. The same argument which has just been used to show tnat when one of the ethers is in motion it will carry with it ether of the same kind, rather than ether of the other kind, can be applied to show that a molecular mass, in which the atom explosion occurring is liberating an excess of one ether, will, when in motion, carry with it ether of this kind rather than ether of the other kind. Con- sequently, if two substances are chosen, in one of which an excess of one, in the other an excess of the other ether is being liberated, and they are moved upon one another, some of the two ethers found, from time to time, disen- tangled from one another (see p. 67) at the surfaces in contact, will be drawn in opposite directions, and will not immediately re-intermix, as under ordinary circumstances they would do. And we conclude that as the ethers, thus from time to time disentangled, flow in opposite directions across the surface separating the moving bodies, in obedience to the law of opposite currents above established, the direction which each ether takes, i.e., which of the two exciting substances it passes towards, will ultimately depend on the relative proportions of the two ethers which the two substances are respectively emitting. Since, as we saw just now, any excess of one ether present at any time around the molecules of a body ordinarily, i.e., unless the body is very perfectly insulated, passes more or less readily away by conduction, and the proportion of the two unmolecular ethers ordinarily present anywhere, is, consequently, that in which they would symmetrically intermix, we conclude that, so far comes out conspicuously hereafter, when we deal with continuous currents of electricity (p. 126). The velocity of the two ethers in opposite directions will evidently depend on the velocity with which the intermixing ethers pass into each other ; it appears to vary according to circumstances. ELECTRICITY LIBERATED BY FRICTION. 77 as the liberation of electricity by friction depends on the disentanglement from each other of the intermixed unmolecular ethers adherent to the molecules of the elec- tric, and not directly on atom destruction occurring at the time, the quantity of positive ether separated in one direction will bear a constant ratio to the quantity of negative ether separated in the opposite direction, i.e., the ratio of the quantities necessary to produce a symmetrical intermixture, and the fact that all experimenters are agreed that equal quantities of positive and negative electricity are developed in cases of the frictional generation of electricity, as well as in other cases to which reference will be made subsequently, goes therefore to show that it is not to the destruction by the friction of the atoms of the electric that the presence of unmixed ethers, or electricity, is chiefly due, but to the separation of the mixed unmolecular ethers present, in the manner described. Bearing on this, we have the experimental conclusions of Peclet, that the quantity of electricity generated is independent of the pressure, and of the breadth of the rubber, measured perpendicular to the axis of rotation, and that it varies as the angular velocity of the cylinder, and even that it is the same for rolling friction as for sliding friction, if the material of the rubber remains unchanged. It is instructive, in this connection, to notice that the same body may, under different conditions of friction or temperature, furnish now one, now the other, kind of electricity. Thus, Canton, in the last century, discovered that, having roughened a glass tube by grinding its surface with emery and sheet lead, it possessed vitreous or positive electricity when rubbed with oiled silk, but resinous or negative electricity when rubbed with new flannel. He found, in short, that positive or negative electricity might, in certain cases, be developed at will 78 >'^WTHEORY OF ELECTRICITY. in the same tube, by altering the surfaces of the tube and the exciting rubber. Further, removing the polish from one half of the tube only, he excited the different electricities with the same rubber at a single stroke, and, curiously enough, the rubber was found to move much more easily over the rough than over the polished half.* Canton likewise discovered that glass, amber, sealing wax, and calcareous spar were all electrified positively when taken out of mercury ; and hence he was led to the important practical discovery that an amalgam of mercury and tin applied to the surface of the rubber was most efficacious in producing electricity in conjunction with glass.f Professor Guthrie has recently called attention to the interesting fact, that while, when flannel is rubbed with ebonite it is positively electrified, and when ebonite is rubbed with glass it is positively electrified, when flannel is rubbed with glass the flannel becomes feebly negative. Glass discs in electrical machines appear to be generally improved by age and use. The consideration of the principle of the electrical ma- chines which act by induction is deferred (see p. 97). Leaving the further consideration of electrical conduction till we deal with the subject of electric currents, we will pass on to consider in the next chapter the subject of statical electrification. * This appears to be an interesting exhibition of our funda- mental property, cohesion. t "Ency. Brit.," Art. "Electricity," p. 7. 79 CHAPTER VIII. ELECTROSTATICS. Attraction and Repulsion. AMONG- the phenomena by which the presence of electricity is ordinarily manifested, attraction and repulsion hold the most prominent place. We all know that when a body is electrified statically by friction, or by other means, it has an attraction for other unelectrified, or oppositely electrified bodies, and that it also has a repulsion for bodies which are similarly electri- fied ; this being shown in the simplest manner by the electric pendulum, which consists of a pith ball suspended by a silk fibre from an insulated support. Thus, when an electrified glass tube is brought near the pith ball, the latter is attracted ; but as soon as it touches the glass tube, the attraction is changed to repulsion, which lasts as long as the ball retains the electricity which it has acquired by the contact. A similar experiment can be shown, employing, instead of the glass tube, any other body which has been electrified by friction ; for example, a piece of resin, which has been rubbed with flannel. And if, while the pendulum exhibits repulsion for the glass, the electrified resin is brought near it, it is attracted ; and conversely, when it is repelled by the resin, it is attracted by the glass, making it clear that the electricity developed on the resin is not of the same kind as that developed on the glass, since the electrified resin and the electrified glass 80 NEW THEORY OF ELECTRICITY. exhibit opposite forces towards any third electrified body, each attracting what the other repels. The electricity which glass acquires when rubbed with silk is what is called positive, or sometimes vitreous, electri- city ; and that which resin acquires by friction with flannel is what is called negative, or sometimes resinous, electricity.* Further, the force of attraction exercised by electrified bodies on bodies which are unelectrified, or oppositely electrified, has been found, like the force of gravitation, to obey the law of inverse squares as to the relation between the intensity of the force and the distance between the bodies. f Thus, if I be the distance between the centres of two spheres, not in contact, one of which is electrified and the other unelectrified, and F the force of attraction sub- sisting between them, then F varies as p, and, if we allow that the attraction exercised by the quantity of electricity present in a conductor varies as this quantity, we have the force between two points, distant /, acting in the straight line which joins them and = f, where q,q' are respectively the quantities of electricity collected at the two points, and the units being properly chosen. Like the force of gravitation, the force of electrical attraction has never hitherto been satisfactorily explained. A theory of gravitation has already been propounded in this treatise (see p. 39), and theories will now be submitted to account for electrical attraction and repulsion. The theory of electrical attraction we have to offer is as follows : According to the theory above given of what constitutes electrification, an electrified conductor contains an appre- * See Note t, foot of p. 64. f This has been approximately determined by Coulomb's torsion balance, to which reference will be made presently. ATTRACTION AND REPULSION. 81 ciable excess of one ether present alone, unmixed with the other ether, in the mass of unmolecular ethers found among its molecules. Further, we conclude that this unmixed ether, which forms the electric charge, in obedience to the law of sym- metrical intermixture, at its confines intermixes with, and consequently moves towards, any small masses of the other ether found unmixed in contact with it (see p. 9), and that in the process portions of the ether which do not im- mediately intermix are drawn along by portions which do, as above explained (see p. 75). If a charged conductor is surrounded on all sides by non-conducting bodies, since the continuity of any unmixed ethers found in bodies of this nature is, as we have sup- posed, continually broken by motions of the non-conduci>- ing matter, the passing outwards of the ether of the charge occurring as just stated, will take place but slowly, portions of this ether from time to time gradually filtering into and through the surrounding medium, and in this way achiev- ing a slow, sometimes imperceptible, but practically con- tinuous radiation in every direction. And the slow motion outwards of portions of the ether of the charge will be accompanied by a slow motion in the opposite direction of the other ether, as the result of the action of the law of sym- metrical intermixture just now referred to (see p. 75). Now, when an electrified body and an unelectrified, or oppositely electrified, body are placed in proximity, we suppose that the radiation of the ether in excess from the former, which we have thus concluded is slowly taking place, encounters less resistance, and is, consequently, greater on that side of it which is nearest to the latter, ether move- ment being facilitated by the presence of the conducting body ; and, if this is so, we have also at the same place a stronger movement of the other ether in the opposite direction. 82 NEW THEORY OF ELECTRICITY. That this will account for the attraction observed we argue as follows : The adhesion or cohesion between the molecular surfaces in the interior of bodies, and the unmolecular ethers in contact with these surfaces will, it is evident, cause a molecular body whose contained ethers are moving more in some directions than in others, to suffer displacement in the direction of the resultant of the various motions of both kinds of ethers (any difference in the amount of adhesion of the two ethers to the molecular surfaces being taken into account). And, therefore, if, as just supposed, the ether radiation from an electrified body placed in proximity to an un- electrified or oppositely electrified body is greater in the direction of such body than in other directions, the electrified body will be drawn in this direction ; and if, further, the movement of the other ether from the un- electrified, or oppositely electrified body towards the electrified body is also stronger at the same place, this body will similarly be drawn in the direction of the electrified body ; in other words, the two bodies will be drawn or attracted towards one another. That the attraction is greater in the case of an oppositely electrified body than in that of an unelectrified body, may, it is evident, be attributed to the radiation produced from the latter being feebler than that produced from the former, and also to the radiation of one kind of ether from the unelectrified body towards the electrified body being necessarily accompanied by a radiation of a corresponding amount of the other ether from the unelectrified body in other directions, the effect of the latter in imparting motion to the unelectrified body in other directions, to a great extent neutralizing the effect of the radiation towards the electrified body. We have some elucidation of the fact of the force of ATTRACTION AND REPULSION. 83 electrical attraction approximately obeying the law of inverse squares, in the familiar property that the amount of radiation from a body which is intercepted by another given body some distance from it, practically varies as the inverse square of the distance, if we suppose that the radiation occurs uniformly in straight lines, which, if produced, would intersect at the centre of the radiating body, and that the second body is always so placed with respect to the first that a straight line joining the centres of the two bodies always passes through the same point on the second body. For this to explain the existence of the law under con- sideration, it appears, however, to be necessary to suppose that the ether radiation occurs with practically the same degree of facility, irrespective of the distance between the bodies, and that the radiation occurring in other directions than that of the second body, is so much weaker than the radiation towards this body as to be negligable. The theory which we have to offer of the repulsion observed when two similarly electrified bodies are placed in proximity, is as follows : Since, when bodies are similarly electrified they contain, the same kind of ether in excess of the other ether, two similarly electrified bodies radiate the same kind of ether, and, as the radiation depends, according to the above, on, the presence in the surrounding non-conducting medium of the other kind of ether to intermix with the unmixed ether of the charge, it is evident that when the two bodies are in proximity, there will, in the case of each, be less, radiation on the side turned towards the other body. Now, since in both conducting bodies the ether in excess, preserves far more continuity than the other ether does, we conclude that the molecular matter of both will partake more fully of the various motions of the. ether in excess, than of those of the other ether. 84 NEW THEORY OF ELECTRICITY. Consequently, we attribute the moving apart of the two bodies to the drag, in opposite directions, on their inter- molecular surfaces (p. 40) of the moving ether of the charge, as this ether radiates into space from their remoter sides more freely than from the sides which are turned towards one another.* Examples of electric repulsion are very numerous, and need not be given here. There is, however, a simple experiment which appears to afford an instance of ether radiation extending the conducting body from which it is taking place. A trough of mercury is divided longitudinally by a non- conducting partition. A varnished wire is bent into such a form that the two extremities of it can respectively float upon the two surfaces into which the mercury is divided, the central portion of the wire forming an arch over the partition. The only portions without varnish are the ends. When the terminals of an electric battery are inserted in the mercury, both at the same end of the trough, one in each division, the circuit is completed through the arched wire, and we evidently have a circuit of variable length, according to the position of the connecting arch of wire which spans the partition. It is found that when the current passes, the wire retreats from the terminals, making the circuit as long as possible, f It may be objected to the above theories, both to that of * Instances of motion imparted to a body through the radiation of some fluid material from it, are, we may remark, familiar to us. We have plenty of examples of motion obtained in this way, in the propulsion of fireworks, through the sudden liberation of rarefied and exploding gases. And we may also mention the movement produced by the emission of steam from an orifice. An example of movement, which we should refer to ether emission, is presented by what are called electric whirls, to which reference is made presently (Note *, p. 109). f Deschanel's " Electricity," translated by Prof. Everett, p. 681. ATTRACTION AND EEPULSION. 85 electrical attraction, and to that of electrical repulsion, that the action of a charged conductor is ascribed to a radiation of the ether, that if this occurs it must gradually draw away the excess of one ether, to which the electrical condition has been ascribed, and that we should have a continually falling potential, and sooner or later find the charge entirely dissipated, and that this appears incon- sistent with fact. For, although under ordinary conditions, electrical charges in insulated conductors are speedily dissipated, this would seem to be due to moisture in the air or on the surface of the insulating support, and more and more stable electrification is displayed as insulation in vacuo is perfected, two sheets of gold leaf, electrically repelling each other, having been known to remain at sensibly the same angle of separation for montLs together.* Perhaps this objection is adequately met by the supposition that the very small waste of the unmixed ether of the charge, which our theory requires us to suppose is occurring in such a case, is completely made good by an excess of this kind of ether set free by mole- cule destruction continually proceeding in the gold, as in all other bodies (see p. 21). The foregoing theory, that it is the radiation of the ethers which produces attraction, receives important corroboration in the sequel, in a reference to some recent experiments by Prof. W. Holtz (see p. 100). Other manifestations of the presence of electricity, such as combustion, incandescence, phosphorescence, explosion, etc., will be found referred to in the sequel. * In ultra gas, a pair of electrified gold leaves have remained repelled, at absolutely the same angle, for thirteen months. Proc. R. S., No. 193, 1879, p. 347. 86 CHAPTER IX. ELECTROSTATICS. Continued. Insulation Electrical "Density" and Distribution. A CCORDING to the above, as well as according to *- experience, the presence of an electric force does not necessarily involve an electric current ; the existence of the bodies known as non-conductors, to which reference has already been made, permitting us to conceive of a space, or electric field, in which an excess of one ether* is present unmixed with the other, but from which, owing to its being completely enclosed by non-conductors, no continuous current is passing. It is evident that equilibrium in such a field is attained when the ether present in excess is so distributed that no ether current exists within the field ; the case being then parallel to the case of water which has found its level in some receptacle. We express in the language ordinarily employed the fact that an electric field tends to this condition of equilibrium when we say that all points within the field are found to be at the same electric potential. As to the nature of the distribution of the unmixed ether, within such a field, when there is equilibrium : * Excess of one ether means, in all cases, the amount of one ether over and above the relative quantities of the two which neutralize each other, apart from the question whether such neutralization is effected by equal quantities of the two ethers, or otherwise. ELECTRICAL " DENSITY " AND DISTRIBUTION. 87 To take the simplest form for such a field. Suppose we have a sphere of metal, or of other conducting material, as the body throughout which the ether shall be free to circulate ; or, in other words, as marking the shape of the electric field ; and that it is supported on a stem of glass, or other non-conductor, so as to be completely enclosed by two non-conductors, air and glass. Now, according to our theories, a large part (subsequent considerations will lead us to believe, by far the chief part) of the unmolecular ethers present among the molecules composing the molecular mass, consists of the two ethers satisfying each other, i.e., in a state of mutual symmetrical intermixture, and only the small excess of unmixed ether present is concerned in producing electrical phenomena. A clue to the distribution of this excess will, we should expect, be given by the electrical phenomena it produces* and, as a matter of fact, we have the following very remarkable, well-known phenomenon. If the insulated sphere we employ is hollow, with an orifice in the top, when a proof-plane, as it is called, consisting of a small disc of gilt paper insulated by a thin handle of shellac, is applied first to the interior surface of the sphere, and, tested by an electric pendulum, or an electroscope,* it is found to exhibit no trace of electricity. But, when next it is applied to the external surface of the sphere, it is found to be electrified, and capable of attracting light bodies, f * The ordinary gold leaf electroscope, for detecting the presence of electricity, and determining its kind, depends merely upon the principle of electrical repulsion of bodies similarly electrified. The instrument known as Coulomb's torsion balance was invented by the investigator of that name to measure quantity of electricity. It is not necessary to particularly describe its construction here, as a description will be found in most electrical treatises ; but it may be stated that it depends on the principle that the torsion of a wire is simply proportional to the twisting couple. f Deschanel's " Electricity," translated by Prof. Everett, p. 524 88 NEW THEORY OF ELECTRICITY. We naturally conclude that the unmixed ether carried off by a proof-plane is simply that which was residing on the part of the surface covered by the proof-plane before its application, the latter being virtually part of the surface of the conductor during the time of its contact. The most striking experiment ever made, demonstrating the above-mentioned fact, is that described by Faraday, in his " Experimental Researches." He constructed a hollow cube (12 feet in the edge) of conducting matter, and insulated it in the lecture room of the Royal Institution, and he tells us, " I put a delicate gold leaf electrometer within the cube, and then charged the whole, by an outside communication, very strongly for some time together ; but, neither during the charge or after the discharge did the electrometer, or the air within, show the least sign of electricity. ... I went into the cube and lived in it, and using all other tests of electrical states, I could not find the least influence upon them, though all the time the outside of the cube was powerfully charged, and large sparks and brushes were darting off from every point of its outer surface." We conclude, therefore, that, in the case referred to, the ether which is in excess, and which, according as it is the more readily compressible or the less readily compressible ether determines whether the electrification shall be posi- tive or negative, is found entirely, or almost entirely, at the outer surface, and not within the body of the conductor. And, generally, it would appear that in all cases where one of the two ethers constituting the unmolecular ethers present among the molecular matter of a body is in excess of the other, the unmixed portion thus in excess passes to the outer boundary of the body, leaving the intermixed ethers, which neutralize each other electrically, in possession of all the interior space allotted to unmolecular ethers.* * An apparent exception to the above-stated law occurs when an ELECTRICAL "DENSITY" AND DISTRIBUTION. 89 The explanation of this, which suggests itself, is that the particles of unmixed ether, which are continually radiating from the surface of the body on all sides, by their motions produce currents of the remaining particles of the same unmixed ether which, setting from the centre to the cir- cumference of the conductor, draw this unmixed ether to the circumference. Next, as to the nature of the distribution of the unmixed ether of the charge at the surfaces of bodies : Coulomb has made several experimental investigations as to electrical distribution, the course pursued being as follows : He touched the electrified body at a known point with the proof-plane, and then ascertained with the torsion balance the amount of torsion requisite to resist the repulsion exercised by the proof-plane thus electrified upon a brass ball charged with the same kind of electricity. He then repeated the process with electricity taken from a different point of the body under examination, and the ratio of the electrical " density " at the two points was given by the ratio of the torsions. It is found that when the proof-plane is applied to different parts of the surface of a conductor the quantities of electricity which it carries off are not usually equal, from which we conclude that equal areas on different parts of the surface of a conductor do not contain equal quanti- ties of the unmixed ether. It is also found that if the charge of the conductor be varied, the quantity of electricity resident upon any speci- fied portion of the surface is changed in the same ratio. electrified body is enclosed within, but insulated from, a hollow conductor, the laws of induction, to which reference will here- after be made, in this case disturbing the conditions under which electrification is ordinarily confined to the surface of a conductor. And in the case of continuous electric currents, we commonly find evidence that the current traverses the interior as well as the surface of the conductor which carries it. 90 NEW THEORY OF ELECTRICITY. The ratio of the quantities of electricity at two specified portions of the surface is in fact independent of the charge, and depends only on the form of the conductor. These facts are usually expressed by saying that distri- bution is independent of charge, and that the distribution of electricity on the surface of a conductor depends on its form. The following are some of the results obtained by Cou- lomb : 1. In the case of a sphere, the electrical "density" per unit of area is the same for all points on the surface. 2. Ellipsoid. The electrical " density " per unit of area is greatest at the ends of the longest, and least at the ends of the shortest, axis ; and the " densities " per unit of area at these points are simply proportional to the axes themselves. 3. Flat disc. The electrical "density" is almost in- appreciable over the whole of both faces, except close to the edges, where it increases almost per saltum. 4. Cylinder with hemispherical ends. The electrical "density" per unit of area is a minimum and nearly uniform, at parts remote from the ends, and attains a maximum at the ends. The ratio of the electrical " den- sity " at the ends to that at the sides increases as the radius of the cylinder diminishes, the length of the cylinder remaining the same. 5. Spheres in contact. In the case of equal spheres, the charge which is nothing at the point of contact, and very feeble up to 30 from that point, increases very rapidly from 30 to 60, less rapidly from 60 to 90, and almost insensibly from 90 to 180. When the spheres are of unequal size, the charge at any point on the smaller sphere is greater than at the corresponding point on the longer one, and as the smaller sphere is continually diminished, the other remaining the same, the ratio of the "densities " ELECTRICAL "DENSITY" AND DISTRIBUTION. 91 per unit of area at the extremities of the line of centres appeared to tend to the ratio 2:1.* According to our theories it is relative quantity of the excess of unmixed ether present at different parts of the surfaces of bodies of different form which is determined in these experiments, and our explanation of the remarkable distribution of this ether which is revealed is as follows : We have concluded that the gentle radiation of the un- mixed ether of the charge which proceeds from the surface of the electrified body draws all this unmixed ether away from the centre to the circumference of the body. When the radiation is uniform it is evident this ether will be drawn towards every part of the circumference equally, but when the radiation is greater at some places than others, the ether movement will be greater towards the places where there is greater radiation. Now the ether radiation will evidently proceed with greater facility where the surface is more convex and least sheltered by any neighbouring prominences, which are themselves radiating the same ether ; and at sharp pro- jections, such as the points or edges of a body, its relative facility will be very great indeed. Therefore the more convex a portion of surface relatively to other portions of the same surface, and the less sheltered by any of these other portions, the more the unmixed ether will be drawn to it, and consequently the greater the pro- portion of this ether which will be found there. * Deschanel's " Electricity," translated by Prof. Everett, p. 529. 92 CHAPTER X. ELECTROSTATICS. Continued. Electrical Induction Electric Shadows. THE next phenomenon which claims our attention is that of Electrical Induction. It is commonly shown by means of the apparatus repre- sented in Fig. 2,* which consists of a sphere c, and a Fig. 2. conducting insulated cylinder AB, from which are sus- pended at equal distances a few pairs of pith balls. The sphere is charged with electricity, but not the cylinder ; and it is then found that if the electrified sphere is brought near to one end (A) of the cylinder, electrifi- cation of the latter, due to the proximity of the former, is evidenced by the divergence of the pairs of balls. The divergence of the different pairs is not however the same, but is less in successive cases from the pair nearest the * This is taken from Deschanel's " Electricity," edited by Prof. Everett, p. 513. ELECTRICAL INDUCTION. 93 sphere until a point M is reached, where there is no divergence. Beyond this successive pairs of balls exhibit increased divergence. The neutral point M does not exactly bisect the length of the cylinder, but is nearer the end A than the end B, and the former end is found to be more strongly electrified than the latter. The two ends of the cylinder are found to be charged with opposite kinds of electricity ; the end A being charged with the different electricity from that in the sphere c, and the end B with the same electricity as that in the sphere c. If the cylinder be brought closer to the sphere the divergence of the balls increases ; if it be removed farther from it, the divergence diminishes. All signs of electricity disappear if the sphere be taken away, or connected with the earth. If, while the cylinder is under the influence of the elec- tricity of c, the end B is connected with the earth, the pith balls at this end immediately collapse, while the divergence of those at A increases, and we find that the whole of the cylinder is now electrified with the opposite electricity to that in c, the neutral line being pushed back to the earth. If the earth connection be now broken, and the sphere c be then removed, the cylinder will remain electrified just as though it had been touched by an electrified body. This mode of giving a charge to a conductor is called charging by induction, and the sign of the charge thus given is always opposite to that of the inducing charge in c. If a series of conductors similar to A B be placed in line, without contact, and the electrified body c be placed opposite to one end of the series, all the conductors will be affected in the same manner as the single conductor ; they will each be charged with the opposite electricity to that in c at the end nearest c, and with the same electricity as that in c at the remote end, the effect, however, becoming feebler as we advance along the series. 94 NEW THEORY OF ELECTRICITY. The explanation of these phenomena which is here offered is as follows : Suppose that the unmixed ether in excess present in the sphere c is positive ether, i.e., of the kind which produces positive electrification. Particles of this ether are, according to the conclusions we have reached, radiating from the electrified sphere to- wards the end A of the cylinder, and producing a radiation from the cylinder of negative ether in the opposite direc- tion. The radiation of negative ether from the cylinder thus set up, we may suppose, from the arguments of the preced- ing chapter, creates a flow which draws out negative ether from the intermixed mass of unmolecular ethers present in the cylinder, and accumulates it so as to form a sort of cap of this ether at the surface at the end nearest to c, the maximum depth or " density " being found at A. Since the unmolecular ethers of the conductor A B are at first all intermixed, the separation of negative ether arising in this way involves the separation of an equal quantity of positive ether ; and as the latter will evidently find the most unimpeded radiation at the end of the cylinder furthest from c, it will similarly accumulate so as to form a sort of cap of positive ether at this end, with a maximum depth or " density " at B. This explanation is consistent with the fact that the larger the conductor A B, the greater the accumulation of negative electricity at A, the greatest accumulation taking place when by connection with earth this conductor is ren- dered " infinite." For it is reasonable to expect that the radiation of the negative ether from the cylinder will be greater the greater the quantity of intermixed unmolecular ethers contained in one continuous conductor from which it is drawn, and the greater the radiation the greater the quantity of ethers separated. ELECTRICAL INDUCTION. 95 We shall presently find experimental reasons for con- cluding that when the conductor A B is very large the quantity of negative ether separated and accumulated at the end A is just that which would suffice to intermix with so much of the positive ether in c as is radiating particles towards A B. It is evident that the two conductors employed in the above experiment, or indeed any number of conductors similarly related, behave, so far as the electrical functions of the extremes of the system are concerned, just like a single, con- tinuous, electrified conductor. How completely a system of bodies, one of which contains an electric charge while the remainder are uncharged until acted upon by induction, thus behave like one single electrified conductor, is well shown by Faraday's experiment with the ice-pails.* Let A (Fig. 3) represent, in sec- tion, an insulated pewter ice-pail, ten and a half inches high, and seven inches in diameter, connected by a wire with a delicate gold leaf electroscope E, and let c be a round brass ball, insulated by a dry thread of white silk, three or four feet in length, so as to remove the influence of the hand holding it from the pail below. Let A be perfectly discharged, and let c, after being charged at a distance, be introduced into A, as in the figure. If c be positive, E also will diverge positively ; if c be taken away, E will collapse perfectly, the apparatus being in good order. As c enters * The description of this experiment is taken from Deschanel's '* Electricity," translated by Professor Everett, p. 526. Fig. 3. 96 ' NEW THEORY OF ELECTRICITY. the vessel A, th"e' divergence of E will increase until c is about three inches below the edge of the vessel, and will remain quite steady and unchanged for any greater depression. If c be made to touch the bottom A, all (that is, practically all) its charge is communicated to A, and c, upon being withdrawn and examined, is found perfectly discharged. Faraday found that at the moment of contact of c with the bottom A, not the slightest change took place in the divergence of the gold leaves. Hence, the charge previously de- veloped by induction on the outside of A must have been precisely equal to that acquired by the contact. And we, therefore, conclude that the quantity of negative ether accumu- lated on the inside of the pail, in the way explained, is, practically, just what would suffice to intermix symmetrically with the positive ether constituting the charge on c. Extending the experiment. Fara- day employed four ice-pails (Fi 6 * cast no shadows. The insulation or non-insulation of the conducting bodies makes no difference in their shadow- giving power. A cross cut out of cardboard casts a well- defined shadow at the centre of the field, but the exterior portions are somewhat hazy." (To give an idea of the curious modification in shape which a plain cross undergoes in its shadow see Fig. 5.) " An ebonite cross casts no shadow. A cross made of two strips, one of cardboard, the other of ebonite, fastened with shellac, casts only a single bar of shadow. Rings of tinfoil, cardboard, or wire also cast shadows. Such small objects are conveniently held by attaching them to the end of glass rods. The size of the shadows increases if the objects are displaced from their central position to right or left. A 102 NEW THEORY OF ELECTRICITY. strip of card or thin metal casts the same shadow whether it be held broadside or edgeways in the field. A wire grating having five millimetres width between the bars obscures the field like an opaque body. Breathing on a strip of ebonite or glass renders its surface a feeble con- ductor, and it casts a transient shadow. A glass rod heated at one point casts a shadow at the heated point, the shadow dying out as the rod cools. No shadow is cast by a conductor whose surface is completely covered by insu- lating material, such as a shellac-covered wire, or a glass tube containing water, but dry externally. The smoke ascending from a cigar casts moving shadows upon the silken screen. If a small ball be fixed upon the left dis- charging-rod in place of the point, the shadow on the silk is poor, but a second shadow is observed upon the surface of the ball ; and this is excessively small, reminding one of the diminished, erect, virtual, optical image in a small polished ball. This one experiment succeeds best if the ball be made the positive conductor. For the other ex- periments it makes little difference whether the electrifica- tion of the point be positive or negative, except that when the point is positively electrified the illuminated surface is a little larger than when negatively electrified. A larger disc of light can also be obtained by working the machine at a greater velocity, but at the same time the shadows are rather smaller The same kind of phenomena have been investigated in America by Messrs. Fine and Magie. They added the interesting observation that the lines of electrical action were deflected by the presence of a conducting body at the side of the field, and the form of the shadow correspondingly altered." Further, Prof. Augusto Righi, of Padua, in a recent memoir on the subject of electric shadows, observes that if the object giving an electric shadow is itself electrified simi- larly to the discharging point the shadow is extended, ELECTKIC SHADOWS. 103 while if it is oppositely electrified or connected with earth the shadow is attenuated. Let us endeavour to explain these interesting pheno- mena : As to the luminosity of the silk-covered surface, a theory is submitted hereafter that light-producing ether waves originate in the concerted explosions of primary atoms (see p. 202), and accordingly we suppose that the luminosity observed is due to atom-explosion produced by the action of the moving ethers of the discharge on the molecular matter of the non-conducting silk interposed in its path. Next with reference to the characteristic peculiarities of electric shadows, the existence of which evidently indicates the withdrawal or diversion of certain portions of the stream of particles of unmixed ether passing from the pointed conductor through the air-space. According to the theories which have been submitted, the motion of positive ether in one direction, and of nega- tive ether in the other through the air-space between tha two conductors is to be attributed to the occurrence of symmetrical intermixture between the two differently com- pressible ethers, and therefore depends on each ether from time to time encountering the other. But we have sup- posed that continuous chains of particles of each ether unmixed with particles of the other are present in con- ducting bodies (p. 66), therefore it is natural further to suppose that in such bodies the radiation of particles of ether is here and there checked, as these particles en- counter continuous patches of the similar ether. Thus we account for the fact presented to us that con- ducting bodies form a barrier to ether radiation though not to ether conduction. The fact observed, that an excess, in the object giving the shadow, of the same kind of ether as that radiating from the point extends the shadow, we shall, consistently 104 NEW THEORY OF ELECTRICITY. with this, attribute to the presence immediately around the object of the ether thus in excess. And, on the other hand, the fact that an excess in the object of the other ether attenuates the shadow, we shall attribute to the similar presence of this other ether inviting intermixture with the ether passing from the point, and thus facilitat- ing radiation. The paths of the radiated ether particles will evidently, according to our theory of ether radiation, depend on the form and extent of the conducting surface behind the silk screen. We suppose further that they are influenced by the occurrence of ether radiation from the object inter- posed, or from neighbouring objects, if such are present ; the power the object interposed has of drawing towards it ether particles which have come from the conductor, depending, accordingly, on its bulk rather than on the pro- file of it which is turned towards the radiating point. 105 CHAPTER XL ELECTRO-DYNAMICS. Ether Currents of Short Duration Electric Condensers Effects of the Presence of the Unmixed Ethers on Molecular Matter. WE have supposed electric conduction to be the result of a flow of unmixed ether, very analogous to the flow of a liquid (p. 65). According to this view, time must be an important element with regard to a flow of electricity in a conductor ; for it is evident that, if the ether does not traverse a closed curve, the flow must be treated as of finite duration, and its effects must be looked for during a finite, and commonly a very limited period. We have, therefore, the important distinction between the electrostatical phenomena we have been considering, and the electro-dynamical phenomena we are now to consider ; that while the former, which we have supposed to be due to motions of inconsiderable quantities of unmixed ether occurring from the surfaces of electrified bodies the ethers percolating through the non-conducting media surround- ing these bodies may be regarded as practically constant during the subsistence of given constant external conditions ; the latter, consisting of electric flows or currents in con- ductors including in this definition all instances which can be attributed to the overflow or displacement of a body of dense unmixed ether of either kind caused by the pressure directly applied of another body of the same ether last only during the period the difference of ether pressure which 106 NEW THEORY OF ELECTRICITY. causes them continues, which unless the ether traverses a closed curve, or the supply of unmixed ethers is very large indeed, must evidently be a very limited period.* As appearing to be instances of ether flows or currents of short duration and unequal quantity during their con tinuance, we may mention the different forms of what is known as the disruptive discharge. This occurs when the electric potential of an insulated conductor is sufficiently raised. We have its most familiar form in the electric sparks which pass from an excited electric, or from the conductor of an electrical machine, or between its various insulated parts. It is generally ac- companied by sound, heat, light, or mechanical effects ; commonly by all these at once. The various forms it takes will be referred to presently. The following explanation of its origin is suggested : When offering a theory of the phenomena of statical electrification (p. 81), we concluded that an electrified in- sulated conductor has an excess of one ether upon it, and that this unmixed ether gradually filters through the surrounding medium, encountering least resistance on the side nearest to any other conductor which will supply the other kind of ether for intermixture with the ether thus given off; the unmixed ether of the change not passing away by conduction, because of the continual rupture of continuity of the portion of it which is penetrating the non-conducting medium, caused by the motions taking place in this medium. Now, if this be so, we may conclude that increase in quantity of the electricity on the electrified conductor is just increase in quantity of the one ether which constitutes the charge, and that this produces increase in the quantity of ether filtering through the non-conducting medium, as * Cases in which we conclude that the ethers traverse closed curves are considered subsequently. ETHER CURRENTS OF SHORT DURATION. 107 shown by the increased electrostatic action, and which increase will, it is evident, be accompanied by a growing independence of the moving ethers of the nature of the non-conducting medium they are traversing, and a con- sequent lessening of the discontinuity which characterizes them in passing through this medium. And thus, if the charge is sufficiently increased, we shall at last between the two conductors, in the line of strongest inductive action, have a continuous thread of particles of the same ether stretching from one conductor to the other, which thread of one ether will, according to the theory of conduction which has been propounded, itself constitute an electrical conductor. We suppose disruptive electrical discharge to be a rush of unmixed ether along the channel thus opened, occurring, much as a rush of pent-up water will do, soon after a small vent has been opened through a dam composed of dis- placeable material. A fact which accords with the state of things we have thus supposed to be immediately antecedent to the occur- rence of the discharge, and which reveals a preparedness of the ether condition of the path along which the discharge is about to occur, is that sparks show a tendency to persist in a path once opened ; indeed it has been recently shown that if electric discharges between the same points occur- ring at successive instants of time be compared, irregulari- ties and peculiarities present in one of the series are found accurately repeated in other discharges in the same series.* The fact that the nature of the discharge is regulated by the shape of the terminals between which it occurs, and by the nature of the non-conductor through which it passes, is also in harmony with our theory. A reference to the various kinds of disruptive discharge will illustrate this : The sparks furnished by powerful electrical machines, which are sometimes a foot in length, have usually a * Lecture by Dr. W. Spottiswoode, at Royal Institution. 108 NEW THEORY OF ELECTRICITY. zig-zag form like flashes of forked lightning, and very frequently finer ramifications branch out from the main track. The luminous appearances, called brush discharges, are produced when a powerful machine is working in a very dry atmosphere, and are the result of discharge radiated into the air ; they may be rendered very conspicuous by presenting a large conducting surface at a distance a little too great for a spark to pass. The shape of this kind of discharge may be roughly compared to that of a Turk's- head broom ; positive electricity gives larger and finer brushes than negative. The explanation of this form of discharge which natur- ally suggests itself is that many continuous threads of particles of the ether of the charge, such as we have above referred to, are simultaneously produced between the discharger of the machine and the large conducting surface. When discharge takes place from the rounded end of a wire projecting freely into the air, the brush is often re- placed by a quiet phosphorescent glow, which covers a greater or lesser extent of the end of the wire. The noise which accompanies the brush discharge is entirely absent in this case. A discharge of this kind is invariably asso- ciated with a current of air to or from (generally both) the glowing conductor,* and Faraday has concluded that it proceeds gradually by convection. It seems pretty clear that it is a variety of the kind of discharge mentioned next. Another form of electric discharge is that occurring from a point. If a metallic rod terminating in a point be attached to the conductor of the electrical machine, elec- tricity escapes in large quantity from the point, which, when viewed in the dark, is seen to be crowned with a tuft * "Enc. Brit.," Art. "Electricity." ETHER CUKRENTS OF SHORT DURATION. 109 of light. A continuous current of air is found to be pro- ceeding from a point thus discharging.* The great accumulation of electricity which occurs at the points or edges of an electrified body, we have referred to the greater facility of ether radiation which is afforded on prominences ; we have only to suppose that the ether radiation is powerful enough to set up .a current of the air particles among which it passes, and we appear to have an adequate source of electric convection. .The smallness of the quantity of ether simultaneously given off accounts for the comparative insignificance of the luminous and other effects of this kind of discharge. The remaining form of disruptive discharge, which it is proposed to refer to here, is the discharge in rarefied gases ; it owes its distinctive character, not so much to the shape or nature of the terminals between which it occurs, although not uninfluenced by them, as to the nature of the non-conductor through which it passes. f In this kind of discharge there is, ordinarily, a dissimilarity between the luminous appearances of the positive and negative terminals ; and in all instances, whatever the density of the gas, there is a tendency on the part of the luminosity to break up into disconnected blocks and, as gas of a less density is employed, to separate from the negative and cling to the positive terminal. Further, when the pressure is considerably reduced, these blocks are replaced by a beautiful system of flakes, or " striae " of light, systematically arranged in concentric curves, or in * This production of an air current is taken advantage of to pro- duce rotation in the electric whirl. t Reference has been already made to the degrees of resistance, or variations of conductivity, exhibited as we obtain different degrees of rarefaction of atmospheric air. It has been stated that the resistance is diminished by rarefaction up to a certain point, at which a reaction sets in, so that a very complete vacuum is a very excellent insulating medium. 110 NEW THEORY OF ELECTRICITY. regular layers, about the axis uniting the two terminals. As exhaustion proceeds the striae become more and more separated, as well as individually thicker. At first mere flakes of light, they gradually increase in thickness until they assume the proportions of blocks of light, sometimes of larger dimensions in the direction of the axis of the tube than in that of the diameter. At the same time the main dark space between the head of the column and a solitary luminosity about the negative terminal, as well as the dimensions of that luminosity itself, increase in length. A dark space immediately surrounding the negative terminal, and limited by the solitary stria, also begins to show itself, and to increase with the exhaustion. This space has been named after Mr. Crookes, who first made a study of it " the Crookes's space." As we proceed yet further, the column retreats towards the posi- tive terminal ; and, at the last stage, the solitary luminosity shares the same fate, the Crookes' space occu- pies the whole tube, and no gaseous illumination whatever remains.* The effect of using a small negative terminal is to greatly increase the resistance! to the passage of the discharge. If this terminal be large the discharge passes with comparative ease. With a small * Taken from a lecture delivered before the British Association, at York in 1881, by William Spottiswoode, D.C.L., LL.D., Presi- dent of the Royal Society. f On Resistance, see p. 150. ETHER CURRENTS OF SHORT DURATION. Ill negative terminal striae are formed only with difficulty, if at all ; with this terminal large they are readily formed. Figure 6 gives an idea of the arrangement of the striae, in the case of high rarefaction. According to the theories that have been submitted, these very striking phenomena must be regarded as indicating some remarkable interaction between molecular matter and unmolecular ethers. It is suggested that they are probably due to symmetrical intermixture occurring between the tenuous molecular matter and the unmolecular ethers, and to the compounds thus formed being distributed in distinct patches between the terminals. And some explanation of how this may occur as a consequence of the supposed nature of molecular matter and of the un- molecular ethers will appear subsequently, when we come to deal with chemical combination (see p. 359). That the appearances presented do indicate the dis- tribution of the rarefied molecular matter in patches, is supported by some observations made by Yvon Zoch upon a new kind of electric dust-figures Tubes of 1 to 3 centimetres diameter, and from 10 to 30 centimetres in length, were closed at both ends by corks, pierced to receive copper wires. In the tubes were placed various powders, bronze powder being chiefly used in preference to others, which, being lighter, adhered to the sides of the tube. One wire was then connected with the positive conductor of an electric machine, from the other the repelled electricity dissipated itself into the air. The experiments were all conducted at atmospheric pressure. When thus treated the bronze powder arranged itself in beautifully-marked ridges, or strata, varying in regularity, according to the original distribution of the powder. A space free from all traces of powder was observed to surround the positive pole. Usually there was a corresponding accumulation 112 NEW THEOHY OF ELECTRICITY. about the negative pole. These ridges or striations were comparable to the stratifications observable in Geissler tubes ; and Herr Zoch shows that variations in the strength of the electric discharges, in the width of the tubes, etc., produce upon the figures similar effects to those they produce on the luminous striae of vacuous tubes.* The production of light of one colour by one rarefied gas, and of light of another colour by another,f and the falling off in splendour of the lights, both at the positive and negative poles, when the rarefaction is very extreme, are facts evidently in harmony with the theory we shall presently offer, that the waves which propagate light are produced by the concerted explosion of primary atoms (see p. 202). Some reference is made, subsequently, to the electric discharges of thunderstorms. Sir Wm. Thompson has found that the electromotive force, { or, as we should say, difference of ether pressure, required to produce a spark in air between two conductors, is disproportionately smaller for large distances than for small ; in other words, that the dielectric strength of a thin stratum of air is much greater than that of a thick one. Taken in connection with our conclusion, that the un- molecular ethers and the air molecules lying close to the free surface of a dense body are at a high density (see p. 50), the question asked by Prof. Clerk Maxwell, in reference to this fact, is interesting. He says, " Is it possible that the air very near to the surface of dense bodies is condensed so as to become a better insulator ?" * Taken from Nature, No. 583, p. 208. f The reason why the colour of discharges in air at common density and temperature is practically white (it is slightly bluish), as compared with the light in vacuum discharges, is suggested here- after, where also reference is made to the colours of discharges in gases. See chap, on Spectrum Analysis. J For definition of this term, see p. 128. ETHER CURRENTS OF SHORT DURATION. 113 With regard to limiting tension, Faraday came to the conclusion " that, when two equal small conducting surfaces, equally placed in air, are electrified, the one positively and the other negatively, that which is negative can discharge to the air at a tension a little lower than that required for the positive surface, and that, when discharge does take place, much more passes at each time from the positive than from the negative surface." This we should be disposed to attribute to the particular proportion of the two ethers being continually liberated in the insulating medium. As we should expect from our conclusions, stated above that the way is paved for disruptive charge by an increase of ether radiation through the insulating medium, and that radiation occurs with greater facility from more convex surfaces disruptive discharge occurs more readily from some parts of a non-spherical conductor than from others ; and thus, if it is desired to halve the charge between two equal conductors of similar form, it is found necessary that they shall be symmetrically presented to each other ; suppose, for instance, they be ellipsoids of revolution, it will not do to make the pole of one touch the equator of the other. With reference to the relative capacity for electricity of similar conductors of different sizes. Suppose that we have two similar insulated conductors of different size electrified so that the same electrical force is exerted by corresponding parts of their surfaces, in other words, so that the same electrical "density " prevails at correspond- ing points,* then, if corresponding points of the two conductors be simultaneously connected with earth, we may conclude from the equality of electric pressure that the initial velocity of the escaping unmixed ether will be * This implies that the ethers are similarly distributed in the two similar conductors. 8 114 NEW THEORY OF ELECTRICITY. the same in the two cases, and, consequently, since corre- sponding lengths on the two conductors are as their linear dimensions, we may conclude that the times occupied in discharge, and the quantities of unmixed ether discharged, will both have the ratio of corresponding linear dimensions of the two conductors. Defining the electrical capacity of a conductor as the quantity of electricity required to charge it to unit potential, we obtain, therefore, the well-known general proposition that the capacities of similar con- ductors are as their linear dimensions. This proposition is usually deduced from the law of inverse squares, but as we have up to this only traced the existence of this law for electrostatic action through in- sulating media, its use in such a way in these pages is evidently inadmissible. Electrical Condensers. As connected with the subject of disruptive discharges we will now offer a few remarks on what are known as electrical condensers. Electrical condensers may be described in general terms as consisting of two conductors, having adjacent surfaces of considerable extent, separated by a thin stratum, or plate, of non-conducting material, generally called a dielectric, extending beyond the conductors. Thus, one of the first instruments of this kind was "Franklin's pane," which consisted of two sheets of tinfoil pasted opposite each other on the two sides of a pane of glass, the tinfoil not extending to the edges of the pane. It is found that conductors thus arranged are capable of receiving a charge of electricity enormously greater than the charge which could ordinarily be imparted to them. One conductor only receives the charge, and the conductor which does not receive it is ordinarily connected ELECTRICAL CONDENSERS. 115 with the earth, and is found, in accordance with the principle of induction already referred to, to have an opposite electrification to that of the conductor to which the charge is imparted. The most usual form of condenser, that known as the Leyden jar, is simply a modification of Franklin's pane, the glass jar taking the place of the pane of glass ; the inner coating of tinfoil, which is carried uniformly to the same height as the outer coating, furnishing the one sheet of tinfoil, and the outer coating furnishing the opposite sheet ; the cork, or stopper, which closes the mouth of the jar merely serves to keep out dust, and to carry a metal conductor connected with the inner coating. Another simple instrument, which combines the functions of an electrical machine and an electrical condenser, is called the electrophones. It consists of a disc of vulcanite, or of some other electric, and of a smooth metal plate fitted with an insulated handle. The vulcanite is electrified by flapping it with a catskin or flannel, and the metal plate then placed upon it ; the latter does not receive a charge directly from the vulcanite, but if momentarily connected with the earth (say by touching it with the finger), and then lifted, it is found to contain an induced charge to a high potential of an opposite sign to that of the vulcanite, the charge being positive in the case supposed. It is usual to fasten a base or sole of metal to the vulcanite, the advantage being that this has good earth contact, and being electrified by induction, strengthens the effect. It is easy to see that the electrophorus is an electrical con- denser of the nature above described, the air-space between the plate and the disc furnishing the dielectric through which the effect of induction is produced. The thinness of this dielectric is the cause of the amount of positive ether collected upon the face of the metal plate being almost 116 NEW THEORY OF ELECTRICITY. equal to the amount of negative ether upon the vul- canite.* The large quantity of electricity which can be stored in a condenser, is evidenced when it is discharged by connecting, or nearly connecting its two conductors by means of some conducting body. The brilliant spark which can be produced in this way from a Leyden jar is familiar to everyone. The theory of electrical condensers, which we have to offer, is as follows : When two conductors are separated by a dielectric, and one of them contains electricity, there is, according to the arguments submitted above, a radiation of particles of the unmixed ether which forms the charge across the dielectric towards the other conductor, and also a return radiation of the other kind of ether, so that positive ether is drawn into the dielectric on one side, negative ether on the other, both ethers moving but slowly through the dielectric, owing to * A curious instance of electricity held in a body in the manner observed in electric condensers, was noticed by Symmer, about the year 1759. In pulling off his stockings in the evening, he had often remarked that they not only gave a crackling noise, but even emitted sparks in the dark. The electricity was most powerful when a silk and a worsted stocking had been worn on the same leg, and it was best exhibited by putting the hand between the leg and the stockings, and pulling them off together. The one stocking being then drawn out of the other, they appeared more or less in- flated, and exhibited the attractions and repulsions of electrified bodies. Two white silk stockings, or two black ones, when put on the same leg and taken off, gave no electrical indications. When a black and a white stocking were put on the same leg, and after ten minutes taken off, they were so much inflated when pulled asunder, that each showed the entire shape of the leg, and at the distance of a foot and a half they rushed to meet each other. Further, if they were separated, and removed to a certain distance from each other, their electricity did not appear to have been impaired by the shock they had had in meeting ; indeed, the experiment could be again and again repeated, till their electricity, gradually wasting, stood in need of being recruited. (Taken from "Enc. Brit.," Art. "Electri- city," p. 7.) ELECTRICAL CONDENSERS. 117 the breaking of their continuity by the motions of the matter composing it, in the way already explained when we treated of non-conduction. Now, it is evident that the shorter the distance the streams of ether have to traverse to pass from one conductor to the other, i.e., the thinner the dielectric, the less will their continuity be broken by the molecular motions of the dielectric, and the more rapid will be their motion, and consequently the greater will be the quantities of unmixed ether drawn into the dielectric. Again, where the density of the unmolecular ethers is less within the dielectric than within the conductors, we have concluded there will be a gradient of falling ether density from within the conductors across the surfaces separating them from the dielectric (see p. 50), and the thinner the dielectric the gentler this gradient will be, if, as just argued, the ether motions are more rapid. Therefore, we conclude that in the case of a very thin dielectric, such as is employed in electric condensers, when an excess of one ether is imparted to one conductor there is a rapid passage into the dielectric of ethers at a high density, one ether from the one conductor, the other from the other, and that the moving ethers maintain a high density for some distance into the dielectric. And finally, although the state of things just described evidently involves the passage between the conductors of much larger quantities of the unmixed ethers than when the conductors are more widely separated, we conclude that a considerable quantity of each ether is drawn into the dielectric, which does not filter much below the surface, and that, while the quantity of ethers passing, in either direction, the centre of the dielectric, at which the ether density is lowest,* is still comparatively small, a relatively * That is, if, as supposed, the density of the unmolecular ethers is less within the dielectric than within the conductors. 118 NEW THEORY OF ELECTRICITY. considerable accumulation of the unmixed ethers takes place just within the dielectric, one ether penetrating a little below one surface, the other a little below the other. Some important facts may be referred to in support of this theory of the condition of the dielectric of a charged electrical condenser. Thus, that it is possible to charge a non-conducting substance with electricity has been well known for a long time, Canton having observed, in the last century, that the air in a room can be electrified positively or negatively, and that it will remain thus electrified for a considerable time. Again, Franklin's experiment of the Leyden jar with movable coatings entirely confirms the conclusion that nearly all the charge, both of positive and of negative ether ? is stored in the dielectric immediately beneath and upon its surface. The experiment is as follows: A jar, with movable coatings, is placed upon an insulating stand and charged in the ordinary way, and then the inner coating is lifted out by a glass hook, so that it may remain insulated until after its removal. Next, the glass is lifted out from the outer coating, so that we have the dielectric detached from both coatings. Finally, both coatings are discharged while distinct from the dielectric , and the condenser is then put together again. When thus restored to its former disposition it is found to contain almost as strong a charge as it contained originally before the charges resident upon its two coatings were removed, an evident proof that nearly the whole of the charge is contained in the dielectric, and not in the metallic coatings. Again, a gradual dragging of the particles of unmixed ether further and further into the dielectric as the ether radiation is continued, and a consequent increased difficulty experienced by the ethers in extricating themselves when ELECTRICAL CONDENSERS. 119 discharge occu)s, are incidents which we should naturally look for if the state of things is as we have argued, and we have the following proofs that these are incidents of the charging of a condenser. When an electric condenser, whose dielectric is glass or shellac, say a Ley den jar, has been discharged by con- necting its two coatings, if we wait a short time we can obtain another, but much smaller spark by again connect- ing them, and other sparks may sometimes be obtained after further intervals. These are called secondary dis- charges, and the electricity which thus remains after the first discharge is called the residual charge. The amount of this residual charge depends, not only on the actual amount of the charge imparted to the condenser, but also has refer- ence to the time elapsed since the condenser was charged ; it is, in fact, not of instantaneous production when a Leyden jar is charged, but grows in quantity for some time after the introduction of the charge ; thus, it is found that after a Leyden jar is charged up to a moderately high potential, the outer coating being in contact with earth, a gradual fall of the potential occurs. This fall, which is rather rapid at first, gets slower and slower until it reaches a certain limit, after which a sensibly constant loss still continues, which is, however, under favourable conditions, but small. If the condenser be charged again to bring it up to the potential reached when the sinking of potential began, the rate of fall or loss is found to be much less than before, and to be not far from the constant limit just referred to. The process may be repeated, and when the rate of loss is thus made sensibly constant the jar is said to be saturated. That the residual charge is quite withdrawn from active participation in the motions of the free portion of the charge has been shown by Kohlrausch's investigations, in which he has proved by measurements taken with an electrometer and a galvanometer that the ratio of the free, or disposable, 120 NEW THEORY OF ELECTRICITY. r ^'v ' charge to the potential is constant, and thus independent of the residual charge. The same investigator has also con- cluded from his experiments that the amount of charge which becomes latent is proportional to the initial potential, that is, operating with the same jar. He has also arrived at the important conclusion that the time which a residual charge of given amount takes to reappear fully may be different according to the way that charge is produced ; the charge reappears more quickly when it is produced in a short time by an initial charge of high potential, than when produced by a charge of lower potential acting longer.* Again, the entirely material nature of the entanglement of the ethers in the dielectric, so that we seem to have pic- tured to us the material particles of unmolecular ether mixed in with the molecular matter, is forcibly suggested by the experiments of Hopkinson, which go to show that two residual charges of opposite sign may be superposed, so that ivhen the discharge occurs they shall appear in succession. In the same direction we have Hopkinson's observation that tapping upon the dielectric facilitates the liberation of the residual discharge. Kohlrausch states that his results have led him to suspect that the " latent " charge is greater for a greater thickness of the dielectric. Faraday made a variety of experiments on the subject, and found the proportions of positive and negative electri- city entangled in the dielectric were equal. He concluded that the cause of the phenomenon was an actual penetration of the two electricities into the dielectric, which he referred to conduction, and appealed to his experiments as showing that the difference between conductors and non-conductors is only one of degree. * "Enc. Brit.," Art. " Electricity," p. 39. EFFECTS OF ELECTRICITY ON MC%ECPXAR MATTEK 121 UFORNIA. The amount of increase of containing power ill c'ondensers is shown to depend on the material of the intervening non- conductor or dielectric. Without going into figures, it may be stated that, other things being equal, the capacity of a condenser is found to be greater when the insulating medium or "dielectric" is shellac than when it is air. The ratio of the capacity in the former case to that in the latter is called the specific inductive capacity of the shellac. The corresponding ratio has been found to be less for glass, and greater for sulphur. Boltzrnann has also recently dis- covered that there is a decrease of the specific inductive capacity of gases when rarefied. This fact is evidently in harmony with the suggestion that the density of unmole- cular ethers present within molecular masses is to some extent proportionate to the density of the atoms composing these masses (see p. 27). Boltzmann obtained the important result with respect to a certain crystalline sphere of sulphur that the specific in- ductive capacity was different in the directions of three different axes, and this also appears to admit of an explana- tion in harmony with our theories ; for the capacity of condensers for storage of the ethers will evidently partly depend on the permeability of the dielectric to these ethers, and we may suppose that in crystals not of the regular system this permeability is different in the directions of different axes.* Effects of the Application of Electricity to Molecular Matter. A number of phenomena produced by electrical dis- charges may be explained in accordance with our theories by supposing that accumulations of the unmolecular ethers are produced by the motions of the unmixed ethers of the * The similar fact as to propagation of light through crystals not of the regular system is referred to subsequently (see p. 272). 122 NEW THEORY OF ELECTRICITY. discharge,* and that these unmolecular ethers, being much more tenuous than the ethers composing the molecular matter with which they come in contact, cause atom ex- pansion and atom explosion to occur in this molecular matter. Phenomena capable of such an explanation may, it is clear, be cited as supporting the suggestion made when we entered on the present branch of our subject, that electricity is the condition of molecular matter which is brought about by contact with a body of one kind of ether present alone (p. 64). To mention some examples : The discharge of a battery through a fine metallic thread produces the molecular disturbance known as incandes- cence, an effect which in a subsequent chapter is attributed to concerted atom explosion (see p. 202). Of cases in which molecular matter is displaced or volatilized by electricity, we may refer to the familiar experiments of puncturing a card or a pane of glass with the charge. The interesting observation has been made that in perforating a card, if the points between which the discharge occurs be not opposite to each other, the perfora- tion takes place close to the negative point, but if arrange- ments are made for exhausting the air, it is found that as the density of the air is diminished the perforation takes place nearer to the centre. Then we have those very palpable cases in which general explosion of the mass occurs through the passage of elec- tricity. Gun-cotton, even when saturated with water, is readily exploded in this way,f and other very familiar illustrations are presented by the explosion of certain * Accumulations of intermixed unmolecular ethers are subse- quently argued to be productive of heat, and most of the phenomena we are alluding to may be regarded as results of heat as a secondary cause. f A further reference to the subject of explosives is made sub- sequently. EFFECTS OF ELECTRICITY ON MOLECULAR MATTER. 123 gaseous mixtures in the instrument known as Volta's pistol. Some milder effects produced in the same way may be mentioned. When a strong electric discharge passes through a fluid, pressure is suddenly transmitted through the fluid in all directions, and, if it be enclosed in a tube, the tube is generally broken, even when the spark is by no means long. When the surface of the liquid is free, a consider- able portion is projected into the air. The researches of Dr. Warren de la Rue and Dr. Hugo Miiller with a very large chloride of silver battery, have of late given the most unquestionable evidence of sudden and considerable molecular expansion produced by electrifica- tion, and that quite apart from the increase of volume due to heat. The experiments were made in a bell jar, con- taining the terminals, and the jar could be gradually ex- hausted after having been filled with air, or other gas. The remarkable phenomenon was observed, on making connection between the terminals and the battery, that, within certain limits of pressure in the bell jar, a sudden expansion of the gas took place, and that as soon as the connection was broken the gas then as suddenly returned nearly to its original volume, though not quite, in con- sequence of a slight increase of temperature. The effect was exactly like that which would have been produced if an empty bladder had been suspended between the ter- minals and suddenly inflated, and as suddenly emptied.* The following phenomena are additionally interesting, on account of the support they afford to our theories of capillary action : If two small balls, connected with the electrodes of a Holtz's machine in action, be dipped in paraffin oil at a * Taken from Nature, No. 556, p. 174, where details will be found. 124 NEW THEORY OF ELECTRICITY. small distance apart, the whole liquid is thrown into violent motion and runs up the wires which lead to the balls, spouting off in little jets ; further, a heaping up of the liquid is observed between the balls, and if one of them be gradually withdrawn from the liquid for a centimetre or so, it raises a column after it, which adheres until the machine is stopped.* The explanation we have to submit is this : We have argued that forces of capillary attraction, and of gravita- tion everywhere act perpendicular to surfaces throughout which equal density of the unmolecular ethers prevails p. 51), and we suppose that the presence of the unmixed ethers which are passing from the electrodes, changes the direction of these surfaces of equal ether density in such a way as to make the surface of the liquid, in seeking equi- librium under the surface attraction to which it is subjected, exhibit the changes observed. Again, Faraday observed that a large drop of mercury, resting on the flat bottom of a vessel containing dilute acid, changes its form in a remarkable way when connected with one of the electrodes of a battery, the other electrode being placed in the acid. When the mercury is made positive, it becomes dull, and spreads itself out ; when it is made negative, it gathers itself together, and becomes bright again. f In this case changes of ether distribution and density within the molecular masses of mercury and acid, adequate to produce the effects observed, should perhaps be partly, or entirely attributed to changes in the quantity and pro- portions of the ethers liberated within these masses, caused by the electric action. J * "Enc. Brit,," Art. " Electricity," p. 66. t Taken from "Enc. Brit.," Art. " Capillary Action," p. 65. | That electric action does sometimes produce this effect is argued, p. 195. EFFECTS OF ELECTRICITY ON MOLECULAR MATTER. 125 As a final example of capillary change produced by electricity, we may mention the familiar experiment of the electric bucket. When a vessel containing a liquid, and furnished with very fine discharge tubes, is suspended from the conductor of the machine, so long as the vessel is not electrified the liquid comes out drop by drop ; but when the machine is turned it issues in continuous fine streams, the quantity discharged in a given time being sensibly the same in both cases.* The lowering of the cohesion of the liquid which this effect indicates would, according to our theory of the nature of the liquid state, be naturally accounted for by supposing molecule destruction within the liquid, and consequent internal ether liberation, to be increased by the presence of the unmixed ether of the charge. In connection with this explanation we may mention the fact first ascertained by the Abbe Nollet 1746 to 1753 that electricity increases the natural evaporation of fluids, and that the evaporation is hastened by placing them in non-electric vessels, f ' Some further important references to the influence of the unmixed ethers on molecular matter will be made in the sequel, when we deal with the subject of Chemistry. * " Deschanel's Electricity," edited by Prof. Everett, p. 558. t The same observer also ascertained that the vegetation of seeds is hastened by electrifying them. 126 CHAPTER XII. ELECTRO-DYNAMICS. Continued. Electric Currents of Long Duration, or Continuing Current. THE well-known phenomena of electricity, which we have touched upon, lead us to conclude that ethers moving by conduction have very great velocity, and also that the presence of any large store of unmixed ether will ordinarily be accompanied by violent action of molecular matter. It is, in consequence, somewhat difficult at first sight to conceive of the existence under ordinary con- ditions of a current of ether which shall have unbroken continuance, and yet not be immediately, or almost imme- diately, exhaustive of its source, and therefore of very short duration ; a reference to the continuous motions of some grosser forms of matter will, however, it is thought, lessen the difficulty. In the case of the apparatus arranged to supply the upper floors of our houses with hot water, the pipes are, as we know, arranged to produce what is called a hot water circulation, and, as this name implies, a continual flow of water traverses the pipes of the circulation in one direction, heated water continually rising from the boiler through one of its connections, and the same water, some- what cooled, returning to the boiler through another of its connections, and one small cistern contains water enough to keep up the continual flow, because the same water is used over and over again. ELECTRIC CURRENTS OF LONG DURATION. 127 Again : "We have another instance of continued flow in the case of a steam boiler, a current of steam being con- tinually emitted whose total bulk is enormously greater than that of the boiler. We suppose that a continuing electric current is an ether current in which conditions are present akin to those of both these cases of continuous flow, and that we have generally (1), A complete circuit of conduction ; (2) A continuous liberation of unmixed ether somewhere in this circuit. Further, that such a current resembles an ether current of short duration, such as we have already treated of in three points, namely, 1. In the motion of one kind of ether generating a motion in the opposite direction of the other kind of ether, so that two opposite currents of the two ethers are always present in an electric circuit* (see p. 75). 2. In equal currents of the two different ethers when they intermingle, neutralizing each other electrically. 3. In the possibility of drawing off electricity from a current, by conduction, just as we should from a charged conductor. And that, on the other hand, it differs from an ether current of short duration in the following points : a. That while two short currents, one of positive, the other of negative ether, travelling simultaneously along a uniform conductor in opposite directions, if they ever meet, cannot without ceasing to be currents continue together ; two continuous currents of opposite kinds, thus travelling along a conductor which forms a continuous circuit, may be regarded as loth simultaneously present at every point in the circuit. * This harmonizes well with experiment and with the statement made in treatises on electricity, that every electric current may be regarded as a flow of positive electricity in one direction, and of negative in the opposite direction. 128 NEW THEORY OF ELECTRICITY. b. That while the electrical energy of a short current depends on the difference of electrical potential at the two points between which it is set up, such a current ceasing so soon as this difference comes to an end, the electrical energy of a continuous current, at any point of its course, depends not only on differences of potential, but also on the quantities of ethers which for the time being are kept unmixed, and which, but for the existence of the current, would be intermixed and neutralizing each other electric- ally." It should be added to the above, however, that in cases when the earth forms part of the circuit, notably in cases of long currents, we may suppose that the unmixed ether of one kind which passes into the earth at one extreme of a conductor does not find its way through the earth to re-enter the conductor at its other extreme, but merely that the same quantity is drawn from the unmolecular ethers within the earth at one end as passes out from the conductor at the other end. Consistently with the above theory of the nature of electric currents, we suggest that the following is the difference between electromotive force, and strength of current, or supply of electricity. Electromotive force between any two points, or dif- ference of electric potential between them, depends, according to our theories, on the quantity of one unmixed ether in excess of the other at each of the two points, and is therefore independent of all unmixed ethers, present anywhere between the points at any moment, which consist of the two kinds in equal proportions, i.e., in such pro- portions that if intermixed they would neutralize one another. Strength of current, on the other hand, depends on * As we have said, the presence of intermixed unmolecular ethers is subsequently argued to produce heat. ELECTRIC CURRENTS OF LONG DURATION. 129 the quantity of the two ethers separated in the current irrespective of the distribution of potential, being regu- lated, it is supposed, by the quantity of the two ethers passing a given point in the conductor in unit of time. According to this, what is known as a strong current at low potential, is a current consisting of a large body of moving unmixed ethers, but so distributed that the pro- portions present at any given point, if intermixed, would nearly neutralize each other. As to the origin of motions of continuous chains of similar ether particles, such as we thus suppose constitute electric currents, We have suggested (p. 67) that in all bodies small masses of intermixed unmolecular ethers are continually here and there temporarily separated into their consti- tuents by the disturbances to which we suppose all matter to be continually subjected ; and it is evident that if this be so, we must everywhere have now and then small quantities of unmixed positive ether and small quantities of unmixed negative ether moving towards one another as the two kinds of particles, from time to time separated, symmetrically intermix again (see p. 75). In the absence of special conditions, small motions of the ethers, thus occurring within a conducting substance, will naturally take place in all directions equally, but in cases where electric currents occur we suppose that move- ments of the ethers produced in most cases* by the liberation of different proportions of the two unmixed ethers at different places in a certain manner cause the small motions of the unintermixed ethers, just referred to, to have cliiefly one particular direction, and thus produce opposite currents of the two ethers in this direction. * We must except the cases in which electric currents are set up by the action of previously existing currents, or by motions of molecular matter. 9 130 NEW THEORY OF ELECTRICITY. The liberation of different proportions of the two ethers at different places we suppose to be caused partly by the presence of different kinds of molecular matter at different places in the circuit, partly by the existence of different conditions of the same matter at different places. Before we endeavour, on the lines thus indicated, to trace more precise theories of the production of eth<>r currents in one or two typical cases, we will offer some evidence that different proportions of the two ethers are emitted by different molecular masses, and that, sometimes, from the same molecular matter the two ethers are emitted in different proportions under different circumstances. First, as evidence that different proportions of the two ethers are emitted by different molecular masses, we have the various phenomena which have already been explained by the supposition that this is so (see pp. 47, 73, and 76, et seq.). And we also have the significant fact that the different behaviour of the elements when in the presence of an electric current, has led scientists to arrange the elements in an electro-chemical series, in which each term is supposed to be more electro-positive than the one pre- ceding it, and thus to have a higher potential when the two elements are in contact.* This series, as determined by Berzelius, is given subsequently ; it is sufficient to say here that the phenomena on which it is based appear to be adequately explained if we suppose that the electro-chemical relation found subsisting between the different elements is determined by the different proportions which they emit of the. two ethers ; that a considerable excess of negative ether is emitted by the element (oxygen) which stands at the head of the series, and that the proportion of positive ether emitted increases in successive terms, till, at the foot of * The electromotive force which generally subsists at the surface of separation when two different substances are in contact is commonly called the contact force. ELECTRIC CURRENTS OF LONG DURATION. 131 the series, we have an element (potassium) emitting a considerable excess of positive ether. Finally we may mention, as supporting the same theory, an experiment made by Sir William Thompson : A ring is formed, one half of which is copper, the other half zinc. This ring is placed horizontally, and a needle made of thin sheet metal is so balanced as to form a radius of the ring. If, when the needle is unelectrified, it be adjusted so as to be over the junction of the two metals, then, when it is positively electrified, it will deviate towards the copper, and, when negatively electrified, towards the zinc. Again, if a whole, instead of a half needle as above, be suspended over a disc made of alter- nate quadrants of zinc and copper, or, better still, inside a flat cylindrical box constructed in a similar way, so that when the needle is unelectrified its axis coincides with one of the diameters in which the disc is divided, then, when the needle is positively electrified, it will take up a position such that its axis bisects the copper quadrants ; if it be negatively electrified, its axis will bisect the zinc quad- rants.* Next, we offer the following evidence, that sometimes from the same kind of molecular matter the two ethers are emitted in different proportions, according to the temperature of the mass, or the chemical conditions surrounding it^ indicating that, under different circumstances, different atoms or different proportions of the same atoms are exploded 4 * Taken from " Enc. Brit.," Art. " Electricity," p. 85. t It is argued, subsequently, that changes of temperature and chemical changes are both due to changes either in the quantity or relative proportions of the two unmolecular ethers present, which act by altering the values of the local pressures referred to (p. 31), so as to lower their minima (see Sections on Heat and Chemistry). The bearing of this on the production of electric currents wiH appear immediately when we examine the various instances of their 132 NEW THEORY OF ELECTRICITY. At the close of the last century, Laplace, Lavoisier and Volta found that electricity is developed when solid or fluid bodies pass into the gaseous state. The bodies which were to be evaporated or dissolved were placed upon an insulating stand, and made to communicate by a chain or wire with a Cavallo's electrometer, or with Volta's con- denser when it was suspected that the electricity increased gradually. When sulphuric acid, diluted with three parts of water, was poured upon iron filings, hydrogen was disengaged with a brisk effervescence, and at the end of a few minutes the condenser was so highly charged as to yield a strong spark of negative electricity. Similar results were obtained when charcoal was burnt on a chafing dish. Volta, who happened to be at Paris when these experiments were made, and who took an active part in them, subsequently observed that the electricity produced by evaporation was always negative. He found that burning charcoal gives out negative electricity ; and in other kinds of combustion he obtained distinct electrical indications. Subsequently, Saussure found that positive electricity is liberated when water is evaporated from a heated crucible of iron or of copper, but negative electricity when it is evaporated from a crucible of porcelain or silver.* We will now, with the aid of the above, endeavour to frame theories of the production of electric currents in certain typical cases. First, let us take the case of feeble electric currents produced by what is known as the therm o- electric pile or thermo-pile. production without the aid of external molecular or ether motions, as it will then appear probable that a necessary condition of this production is that differences shall prevail in different parts of the same molecular mass such as would, according to our argument, produce from similar molecules emission of the two ethers in different proportions at different places in the mass. * Taken from " Enc. Brit.," Art. " Electricity," p. 9. ELECTRIC CURRENTS OF LONG DURATION. 133 The principle of this delicate instrument for determining slight differences of temperature is based on the fact that, if heat or cold be applied to one of the junctions in a circuit composed of two different metals, an electric current is produced in the circuit. This was first dis- covered by Seebeck in 1821. It may be illustrated by employing a rectangular frame having three sides formed of a strip of copper plate bent into the requisite shape, and the fourth of a cylinder of bismuth. The frame must be placed vertically in the magnetic meridian with a magnet- ized needle in its interior. On heating one of the junctions with a spirit lamp, the needle is deflected in such a direction as to indicate that positive electricity is flowing from the hot to the cold junction in the copper portion of the circuit, and from the cold to the hot in the bismuth portion.* If cold instead of heat be applied to one junction, the direction of the positive electricity is still from the warmer junction through the copper to the colder junction, and from this through the bismuth to the warmer junction. If antimony is employed, instead of copper, the effect is more powerful.f According to Becquerel's experiments, the metals may be ranged in the following order as regards the direction of the current produced by heating a junction of any two of them : Bismuth, platinum, lead, tin, copper, silver, zinc, * It is usual to regard the direction taken by the positive electricity as the direction of a current. t In constructing a thermo-pile, the effect of the difference of temperature between two junctions in a circuit composed of two metals is multiplied by constructing a circuit of a number of pieces of two metals (antimony and bismuth), so arranged that the metals are placed alternately in the circuit, and that the junctions are, as to one-half of their number, presented at one end, and, as to the other half, at the other end of the pile ; and the junctions brought together, and subjected to the same temperature, being in both cases the alternate junctions. 134 NEW THEORY OF ELECTRICITY. iron, antimony ; that is to say, if a junction of any two of these metals be heated, the direction of the current at the junction in question will be from that which stands earlier in the list to the other. His experiments have also established the important fact that the current obtained by heating all the junctions of a chain of bars of dissimilar metals to one common temperature is the same (saving resistance) as that obtained by removing the intermediate bars, and uniting the two extreme bars directly to each other, and then heating the junction to the same tempera- ture.* Slight impurities and variations of physical condition are often found to alter the position of a metal in the series. Iron is a remarkable instance of such variations. Thus Joule has found the following order to hold cast iron, copper, steel, smithy iron. It has been found, too, that for every two metals there is a particular temperature called their neutral point, such that a circuit composed of these metals will give no current when one junction is just as much above the neutral point as the other is below it This holds in every case when the difference of temperature between the junctions is small, and it generally holds as far as differ- ences of some hundreds of degrees. If one junction is kept at a constant temperature lower than the neutral point, while the other, initially at the same temperature, is steadily raised, the current first increases to a maximum, which it attains when the neutral point is reached, then decreases to zero (according to the above law), and then becomes reversed, with continually increasing strength. These changes can be shown with copper and iron wire. For if a piece of iron wire is joined at both ends to copper wires, and the copper wires are led to a delicate galvano- * Taken from Deschanel's " Electricity," edited by Prof. Everett, pp. 652 and 653. ELECTRIC CURRENTS OF LONG DURATION. 135 meter, when one of the two junctions is gently heated, a current is produced which deflects the needle in one direction ; but if the heating is continued to redness, the needle comes back, and is still more strongly deflected in the opposite direction.* The following explanation is offered of the simple case of a current in a circuit composed of two metals having two junctions, one at a higher temperature than the other. In harmony with what was stated above (p. 131), we suppose that hi the case of each piece of metal different proportions of the two ethers are being disengaged at the two differently heated ends, and that a difference of electrical potential subsists not only between the two ends, but also, since there is a gradation of temperature from one end to the other, between any two succeeding points in the piece. Now, if the circuit were composed of two similar pieces of the same metal, whose ends were thus differently heated, corresponding ends coming together, it is evident that a precisely similar difference of potential would be found between the ends of one piece as between the ends of the other ; and, in the endeavour after equilibrium, we should have precisely similar flows of one kind of ether starting in opposite directions from one junction to meet similar diverging flows of the other kind of ether starting from the other junction ; and whatever effect was produced by one flow would be neutralized by the similar effect pro- duced by the other in the opposite direction. But in the case under consideration the two ends of the one piece of metal are connected by a piece of a different metal, and we have concluded that two different elements when at the same temperature, or, to speak more generally, when subject to similar ether conditions, suffer a different * Taken from Deschanel's " Electricity," edited by Prof. Everett, p. 654. ' .. . / 136 'NEW- THEORY OF ELECTRICITY. -' . ~V* ' * ..'-' amount of molecule destruction, setting free different pro- portions of the two ethers the difference depending on the ether constitution of the atoms of the two elements respectively and therefore we must look for inequality between the differences of potential in one metal as com- pared with the differences of potential in the other metal ; we may, in fact, find the order of potential reversed, one metal showing a rise from the hot to the cold junction, while the other, at the same temperatures, shows a rise from the cold to the hot ; and, in any case, if the difference of potential is unequal in the two cases, the effect of the difference of potential in one piece of metal will be dif- ferent from the effect of the difference of potential in the other piece of metal. It is true that, taking the point of highest potential in a circuit and the point of lowest potential, there is the same amount of fall in both directions, but the fall in one direction is of a different nature from that in the other ; for in one direction, where the same applied temperature produces a different electrical potential in two different metals, we have a sudden fall across a junction, while in the other direction we have a gradual fall of potential due to a gradation of temperature in the same piece of metal ; and it is reasonable to suppose that a gradual fall of poten- tial has greater effect in producing ether motions in one direction than a sudden fall of potential to the same amount has in producing such motions in the opposite direction. We suppose, therefore, as suggested above (p. 129), that as a net result of the various differences of ether liberation at different parts of the circuit ani consequent differences of potential, we have movements of the newly-liberated ethers along the circuit. Finally, we suppose that these movements of the newly- liberated ethers cause the small ether motions of reinter- mixture continually occurring, which have been referred to ELECTRIC CURRENTS OF LO&G gUKATION. ). 129), to have one particular principaF*o*irection, the direction of the current, and thus cause opposite currents of the two ethers in this direction. That falls of potential to the same amount, but of different natures in a circuit, exert different effects, as just supposed, seems indicated by some experiments of Le Roux, who has shown that where there is dissymmetry in the ends of similar wire brought together at a junction e.g., where an edge of one end is pressed on the flat surface of the other, where the ends overlap or cross, or where the chisel-shaped end of one wire fits into a notch in the end of the other, and the axes of the wire are inclined, and so on the heating of one side of the junction pro- duces a current. With regard to the phenomenon, above alluded to, of the reversal of the current, when the temperature of one junction is made sufficiently high, that of the other junction being sufficiently low ; this evidently accords with the conclusion that the proportion of the two ethers set free by molecule destruction is different at different temperatures. As to the fact discovered by Becquerel, that the current obtained by heating all the junctions of a chain of dissimilar metals to one common temperature, is the same as that obtained by uniting the two extreme bars of the chain directly to each other, and heating their junction to the same temperature (the junction of the end bars to complete the circuit, being in both cases at a different temperature), it is easily seen that whenever a bar has its two ends at the same temperature, there is no gradation of potential throughout it, and the ethers disengaged by the destruction of its atoms, will pass as- much in one direction as in the other, and thus the bar will exercise no more influence in the production of a current in one direction than in the other. And it is, therefore, in harmony with our conclusions, that when such a bar is removed, and th e 138 NEW THEORY OF ELECTRICITY. circuit closed up again without it, no alteration takes place, so far as the production of a current is concerned, saving, as has been said, the resistance due to the bar, to which reference will be made hereafter (p. 150). Herr Schulze-Berge, of Berlin, has attempted a deter- mination of the electric phenomena which occur on contact of metals and gases. Among other observations, he finds that ozone makes gold, platinum, and brass negative to a plate of the same metal in air ; also that hydrogen always makes platinum strongly positive, while its influence on gold is hardly perceptible, and on brass qualitatively various ; great variability was, however, generally found in repetitions of the same experiment.* The fact that a thermo-electric current may be set up in a circuit composed of the same metal in different molecular states, we conclude to be identical with Joule's discovery, above referred to, that the same metal in different molecular states occupies different positions in the thermo-electric series. It indicates, according to the preceding arguments, that in different states the same metal emits different proportions of the two unmolecular ethers. As an instance of the fact referred to : If a knot or a helix be formed in a piece of platinum wire, and heat applied at one side of it, a current is indicated by a delicate galvanometer. And, as another instance, we have the following experiment due to Magnus. On a reel, formed by crossing two pieces of wood, are wound several turns of hard-drawn brass wire, softened in a number of places adjacent to each other on the reel. The free ends of the wire being connected with a galvanometer, and the parts of the wire lying between neighbouring hard and soft portions being heated, a thermo-electric current of con- siderable strength is obtained, whose direction is from soft parts to hard across the heated boundaries. Effects of a * Nature, No. 600, p. 617. ELECTRIC CURRENTS OF LONG DURATION. 139 similar kind were obtained with silver, steel, cadmium, copper, gold, and platinum. In German silver, zinc, tin, and iron, the current went from hard to soft across the hotter boundary.* As further instances : Sir William Thompson has obtained similar results, in the case of the same metal subjected to different degrees of strain. And, finally, it is not uncommon in the case of metals which are usually heterogeneous in their structure, such as bismuth, to find currents produced by heating parts which appear quite uniform.! The experiments of Magnus have shown, that where every part of a circuit, composed entirely of one metal, is in the same state as to hardness and strain, no thermo- electromotive force exists, no matter what the variations of the section or form of the conductor, or what the distri- bution of temperature in it may be, so long as there is neither discontinuity of form nor abrupt variation of tempera ture.J A property of circuits composed of dissimilar metals, the converse of that above referred to, was discovered by Peltier. He found that when an electric current passes over a junction of antimony with bismuth, in the direction from the former to the latter, there is an increase of temperature at the junction, and, when the current passes in the opposite direction, there is a decrease. An explanation of this will be attempted when we come to consider the subject of heat. The flow in opposite directions of the two ethers in a circuit, due to ether motions arising from interaction between different metals, which has just been explained, seems to be exemplified by an experiment made by Volta, of which the following is a simplified form. * "Enc. Brit.," Art. " Electricity," p. 95. t Deschanel's " Electricity," translated by Prof. Everett, p. 653. I "Enc. Brit.," Art. " Electricity," p. 95. 140 NEW THEORY OF ELECTRICITY. The upper and lower plates of a condensing electroscope are made of different metals, say copper and zinc respec- tively. Let the upper plate be laid upon the lower, and the metallic contact ensured by connecting them for an instant by means of a wire. If the upper plate be now lifted vertically upwards, the gold leaves of the electro- scope diverge, indicating that the zinc plate has become positively electrified to a considerable potential.* We suppose that in this experiment, during the instant for which the plates are in metallic contact, a flow of the two ethers takes place in opposite directions, which drives negative ether into the dielectric next the copper, and the complementary positive ether into the dielectric next the zinc, and that the ethers remain stored up in the dielectric, as previously explained, so long as the plates remain to- gether, but are released when the upper plate is lifted (p. 116). Let us next endeavour to explain the production of electric currents in what is known as a Voltaic Battery. The simplest form of Voltaic battery, that which Volta, the discoverer of this means of liberating electricity, ori- ginally experimented with, consists of a pile of a number of pairs of zinc and silver plates, separated from each other by pieces of wet cloth. Hence, the order of the layers, starting, say, from the bottom, is zinc, wet cloth, silver, zinc, wet cloth, silver, and so on ; the lowest plate of all is zinc, the highest silver. When the highest and lowest plates are connected by a conducting wire, a current is found to be traversing the circuit thus completed, positive electricity passing from the bottom plate of zinc up through the pile to the top plate of silver and down through the wire. Now, if we disregard the cloth, which we will suppose * "Enc. Brit.," Art. " Electricity," p. 83. ELECTRIC CURRENTS OF LONG DURATION. 141 is merely a receptacle for the water, we have here four elements, namely, zinc, silver, and the two components of water, oxygen and hydrogen.* To trace the effect of these elements on each other is the function of chemistry, and therefore properly belongs to a subsequent chapter, but we must slightly forestall the treatment of the matter here. Confining our attention to a single layer of each sub- stance i.e., to one segment of the pile, consisting of a plate of zinc, a layer of water, and a plate of silver, we observe first that, judging by the position of the zinc in the electro-chemical series to which reference has been made, positive ether predominates in the unmolecular ethers emitted by this element, that the proportion of positive ether is less in the emissions from the element silver, and still less in those from the element hydrogen, while in the ether emissions from the element oxygen negative ether very largely predominates, this element being indeed, as already remarked, at the head of the electro-chemical series. If, therefore, as already argued, molecule destruction is everywhere going on, and the metals and the water both have unmolecular ethers in a highly condensed state present among their molecules, we may conclude that, at any given moment, the zinc will have present within it a greater excess of positive ether than is present in the water, and that as the excess of positive ether in the zinc proceeds to intermix symmetrically with the excess of negative ether in the water, a small flow of positive electricity will take place from the zinc towards the water, and a small flow of negative electricity in the opposite direction, from the water towards the zinc. A similar effect, in which, however, the movements of the respective ethers have the opposite directions, will, we * The theory of chemical combination subsequently offered will be found to justify the supposition that the qualities of the indi- vidual elements composing a compound are traceable in the com- pound. 142 NEW THEORY OF ELECTRICITY. must conclude, take place between the silver and the water ; but as this will, judging by the relative positions of the zinc and the silver in the electro-chemical series referred to, be less considerable than the effect produced between the zinc and the water, the net result, according to the argu- ments used with respect to a thermo-electric circuit, will, presumably, be the production of a feeble current in the circuit, in which the direction of the positive ether is from the zinc towards the water. To account for the comparatively strong current actually found, we must carry the argument a step further. The unmixed positive ether which is moving in one direction, and the unmixed negative ether which is moving in the other, will have their movements checked, and symmetrical intermixture with one another facilitated wherever they encounter the less-conducting material the water and thus at the boundary, between the zinc and the water, an accumulation of the intermixed unmolecular ethers will take place. And if we suppose that the mole- cular nature of the zinc and also of the water is such that the presence of an accumulation of the unmolecular ethers in contact with them produces considerably increased atom expansion and molecule destruction,* we have a source of considerable liberation of unmixed positive ether from the zinc and unmixed negative ether from the water, such as would, in the way already explained, supply motive power adequate to set up comparatively strong currents of the two ethers in the circuit. As in the case of thermo-electric currents, we suppose that the moving ethers of the currents are largely, and, indeed, chiefly drawn from the general mass of unmole- * See p. 24. The facts that heat and chemical action are produced are, according to subsequent reasoning, evidence of the occurrence of these changes. ELECTEIC CURRENTS OF LONG DURATION. 143 cular ethers present in the circuit, the function of the freshly emitted ethers being chiefly directive, determining that the motions of reintermixture of the unmolecular ethers which are above referred to (p. 129) shall take place chiefly in one particular direction. The efficiency of silver, as the other metal employed with the zinc, appears to lie in its furnishing a good conductor to the ethers moving in the circuit, and in its not being readily acted on by any accumulations of intermixed unmolecular ethers ;* for if it were readily acted on, we should have ether liberation tending to set up currents similar to those set up by the zinc, but in the opposite direction. The repetition of the layers, which constitutes the voltaic pile, it is suggested, merely intensifies the effect by con- tinually adding impetus and volume to the positive ether travelling in the one direction, and to the negative ether travelling in the other direction. It is suggested that the material point in which the various voltaic batteries differ from the original voltaic pile, which has just been explained, is, that the liquids they contain in place of simple water are of a nature to produce greater molecule destruction, and consequent greater ether emission ; this would account for the stronger currents obtained. Cruikshank's trough battery, for example, consists of a rectangular box, or trough, of baked wood (which is a non- conductor) divided transversely into compartments by partitions, each consisting of a plate of zinc and a plate of copper soldered together ; these partitions all have their copper faces turned towards one end of the trough, and, consequently, all their zinc faces towards the other end, and the compartments formed have dilute acid poured into them, to take the place of the water in Yolta's pile. * According to subsequent arguments the silver remaining practically uncharged is evidence that this is so. 144 NEW THEORY OF ELECTRICITY. And the considerable ether motions, which we suppose the strong action of such a battery indicates, we attribute to the large proportion of electro-negative elements which is present in the liquid employed ; this, according to the arguments above given, being productive of stronger motions of newly-liberated ether, and more considerable accumulations of the intermixed molecular ethers to act on the molecular matter. In harmony with these views, the well ascertained fact, that no pile or battery can generate a sensible current except by a sensible consumption of its materials in chemical action, is interpreted to indicate that molecule destruction is always the ultimate cause of electric cur- rents. The following definitions apply to galvanic batteries generally : The difference of potential between the two terminal plates, or extremes, of a battery is called the electromotive force of the battery. Its amount is commonly measured by means of Thomson s quadrant electrometer. These terminal plates, or extremes (that is, the zinc of the first and the copper of the last cell where zinc and copper are used), are called the electrodes or poles of the battery ; these names also being extended to the con- ducting wires in contact with these extremes. As already stated, the direction in which the positive electricity passes is spoken of as the direction of the current. When the plates are of zinc and copper, the zinc is the negative, and the copper the positive electrode ; and this, according to the above theories, indicates that the positive ether flows through the cells from the zinc to the copper, and the negative ether from the copper to the zinc. It is unnecessary to describe here the numerous varieties of galvanic batteries which have been invented ; but we ELECTRIC CURRENTS OF LONG DURATION. 145 shall refer to one or two typical batteries for the purpose of calling attention to some interesting phenomena asso- ciated with voltaic action. The battery known as HarJs deflagrator consists of two very large plates of zinc and copper rolled up together upon a central cylinder of wood, thus forming a helix in section. The plates are prevented from touching each other by pieces of cloth or twine inserted between them. The roll is plunged in a tube of acidulated water, and terminal wires connected, one with each plate. This form of battery furnishes strong currents of comparatively low potential, which, when checked by reduced conduction, produce great heat effects. The explanation offered of this feature, to which the battery owes its name, is as follows : If, as we have supposed, an electric current consists of the two ethers uniniermixed with each other moving in opposite directions, the strength of a current, or amount of ethers composing it, will largely depend on the degree of conduction afforded in the circuit ; if the conduction is good, or, in other words, the flow of the unmixed ethers comparatively uninterrupted, we may look for a strong current. On the other hand, ready conduction will tend to equalize potential, and may therefore be expected to be associated with low electromotive force. The strong currents of low potential given by a Hare's deflagrator appear, therefore, to be the natural result of its low internal resistance to the passage of the unmixed ethers. A defect to which all one-fluid batteries are more or less subject is called local action. It is the action which still goes on at the surface of the zinc exposed to the acid solution when the external communication between the plates is broken. It is generally supposed to arise from inequalities in the zinc, which render one portion of its 10 146 NEW THEORY OF ELECTRICITY. surface electro-positive to another portion, and cause minute currents to pass just as between plates of two different metals. And this explanation is shown to be reasonable by the fact that a very sensible current may be obtained if we use one metal only instead of two to form the plates of a galvanic battery, provided the metal be in two different states. Thus, by melting zinc repeatedly, and pouring it into cold water, a metal is obtained on which dilute sulphuric acid acts very feebly ; and if a plate of this metal is used with a plate of ordinary zinc, a battery cell may be formed with these instead of with zinc and copper. That this is the correct view of the cause of local action is also indicated by the fact that it specially occurs with ordinary commercial zinc, and that the evil is remedied by amalgamating the surface of the zinc plate. What is known as Ritters secondary pile appears to furnish an instance of a metal passing temporarily into different electro-chemical states. This instrument consists of a number of discs, all of the same metal, separated by pieces of moistened cloth. If its two extremities be connected for a few seconds with the poles of a battery, the pile is found to have acquired the power of producing for a short time a current opposite in direction to that which proceeded from the battery. The explanation we have to offer is, that exposure to the different potentials of electrification found at the two poles of the battery, like exposure to different tempera- tures, produces different degrees of molecule destruction in discs differently situated in the series (see p. 132), and thus causes them to act like different metals, or like the different qualities of zinc above referred to. Perhaps, however, the phenomenon is partly due to actual storage of the ethers, such as is referred to immediately (see p. 149). There are two serious preventives to the continued ELECTRIC CURRENTS OF LONG DURATION. 147 action of galvanic batteries. One of these arises from the chemical action between the zinc and the acid (where zinc is used), producing a chemical compound, and gradually impoverishing the acid solution, so that it becomes less and less capable of acting on the zinc. The other, which is the more serious, is known as polarization, and is quite universal in galvanic batteries, so that when a battery is first started the initial electromotive force disengaged always begins to fall off from this cause ; and the same thing occurs whenever we insert an electrolyte into any current. Polarization, which is due to the alteration of the plates (electrodes), is a phenomenon which deserves our attentive consideration for a few moments, as there are some features of it which are very suggestive in con- nection with the foregoing theories. Two different kinds of change at the surface of the electrodes are productive of polarization. Thus, if we compare the effects in a cell containing concentrated sulphuric acid, in which is inserted two electrodes of copper, with those in a similar cell in which electrodes of platinum instead of copper are employed, we find that in both cases the insertion of the cell into a current weakens the current, but that they differ in the following respect that in the first case a definite compound, copper oxide, is formed upon the surface of the positive electrode, but that in the second case the oxygen is merely deposited upon and within the positive electrode in a highly condensed state ; that it is, in fact, in the latter case, as there is reason to believe, alloyed with the platinum of the elec- trode.* The difference in the effects consequent on these two different kinds of change is clearly shown if we test the positive electrodes against fresh plates of similar metal ; for we find that the platinum plate which served as posi- * See Note * , p. 340, 148 NEW THEORY OF ELECTRICITY. tive electrode then gives a strong current, whereas the corresponding copper plate gives scarcely any.* It seems probable that in the case of the oxidation of the copper electrode the polarizing effect is partly due to the loss of conductivity in the circuit, this retarding the two ethers of the current and facilitating their intermixture ; but it may also be partly due to additional ether liberation occurring at the oxidized surface during the passage of the current, and producing a counter current. As to the other case, that of the platinum electrodes, the following facts are generally regarded as proofs that the polarization is due to a change in the plates employed: (1) The substitution of a fresh plate, in place of the polarized plate, immediately restores the electromotive force of the current. (2) The deposited gas may be removed by washing the plate with water, potash, or nitric acid. (3) The polarized condition may be produced with- out inserting the plate in a current at all, if platinum be alloyed with oxygen, by bringing it into the presence of this element in the form of ozone, f The cause of the phenomenon is probably twofold : For, first, we observe that the change in the platinum plates arising from the occlusion of gas, in other words, from their being alloyed with another element, will be likely, according to our arguments, to cause them to emit a different proportion of the two ethers, and will thus account for * "Enc. Brit.," Art. "Electricity," p. 87. t A plate of platinum is rendered electro-positive, to a fresh plate if it is alloyed with hydrogen by immersing it in this gas. The competency of different gases to produce different states of the same metal, is well shown by the gas battery of Grove. Two long glass tubes, A and B, are arranged in the two necks of a Woulfe's bottle. The upper ends of the tubes are closed, but pierced by two platinum wires, to which are fastened two long strips of platinum foil (which are sometimes platinized), reaching to very near the lower ends of the tubes. The bottle and part of the tubes ELECTRIC CURRENTS OF LONG DURATION. 149 polarized plates, used with fresh plates, acting like two different metals as above stated. ' Secondly and this having regard to the considerable secondary currents sometimes produced by polarization, is, perhaps, the principal cause the alloying of the plates with condensed gas will, we conclude, to some extent, destroy their conductivity, and cause them to act as electric condensers, so that they are able to entangle and store up some of the ethers of the current, to give them up subsequently in a direction opposite to that from which they came. It is interesting to notice the great rapidity of the rise and fall of polarization which sometimes occurs. Thus, for instance, Edlund has found that in a certain case the electromotive force of polarization reached '057 of a Daniel! in about J^th of a second, and Bernstein has recently stated that platinum plates, polarized to 1*85 of a Daniell, fell, when the resistance of the circuit was 7*46 Siemens units, to 1'57 in '00111 seconds. The electrolytic action by which the hydrogen passes in the same direction as the positive current is explained hereafter. are filled with some liquid, say dilute sulphuric acid, and hydrogen is introduced into B, and oxygen into A, either by sending an electric current from A to B, and decomposing the dilute acid, or by some other means. This arrangement has an electromotive force comparable with that of a Daniell's cell, and if the original volume of hydrogen in B be twice that of the oxygen in A, it will continue to send the current through a closed circuit, the gas gradually disappearing in the tubes until none is left, when the current stops. (See " Enc. Brit.," Art. " Electricity," p. 87.) 150 CHAPTER XIII. ELECTRODYNAMICS. Continued. Electrical Resistance Ohm's Law. IT is found that the gradual fall of potential in the direc- tion of the current, found subsisting in a uniform portion of a thermo-electric circuit, is a perfectly universal condition in all electric circuits, so that it may be stated generally ; that when a steady current is flowing through a galvanic circuit, there is a gradual fall of potential in every uniform conductor which forms part of the circuit, the fall being in the direction of the current. As in the case of thermo-electric circuits, the gradual falls must, it is evident, be exactly compensated by the abrupt rises (diminished by the abrupt falls, if any) occurring between the various dissimilar bodies forming part of the circuit, and which abrupt rises or falls will be attributed to the liberation of ethers through atom destruction occurring in different parts of the circuit. If we neglect the effect of ethers set free through atom destruction occurring in a uniform good conductor forming part of a galvanic circuit, the gradual fall of potential in such a conductor is, it is suggested, due to the continual withdrawal from the current of equal quantities of the two ethers from time to time symmetrically intermixing. Thus if the quantity of positive ether passing a given point in the conductor in unit of time is a, and the quantity of negative ether passing in the opposite direction, another given point further along the same conductor, in a unit of ELECTRICAL RESISTANCE. 151 time, is 6, we suppose that the cause of the lower potential found at the second point, is that a certain quantity, c, of positive ether is withdrawn between the two points, reduc- ing the quantity passing the second point, in unit of time, to a c ; and that this withdrawal is due to symmetrical inter- mixture of this quantity, c, of positive ether with an equal quantity, c, of negative ether, thus reducing the quantity of negative ether passing the first point, in unit of time, to b-c. In this case the total quantity of both ethers withdrawn will evidently be 2c, and the excess of positive over negative ether passing in unit of time, will be less (alge- braically) at the second point than at the first by the same quantity 2c. The theory that the gradient of potential is caused by the symmetrical intermixture of the ethers of the current, is supported by the fact that heat is always produced ; for we shall presently submit evidence that heat is caused by the presence of symmetrically intermixed unmolecular ethers. It is further supported by the fact that when we compare similar conductors composed of different material, we find, other things being equal, that the steepest gradients of potential occur in substances which are bad conductors, this being what we should naturally expect if the "resistance," as the power possessed by a conductor of causing a gradient in potential is usually called, is due to symmetrical inter- mixture, and if, as we naturally conclude, non-conductors favour intermixture, not only by hindering the passage of the unmolecular ethers, but also by the vigorous molecular motions we have attributed to these bodies. In consequence of the fact that bad conductors give steep gradients of potential, or high resistance, it is customary to regard the order in which conducting bodies stand as to resistance as the order of their conductivitv. 152 NEW THEORY OF ELECTRICITY. All experimenters agree in concluding that gold, silver, and copper manifest least resistance. The order of least resistance is found experimentally to be the same as the order of thermal conductivity, in other words, the order of resistance is precisely the inverse order of thermal conductivity. The suggestion that greater resistance is due to greater intermolecular motion, and consequent checked conduction, receives support from the following : The resistance even of the best conducting liquids, except mercury, is enormously greater than that of metals. For instance, in round numbers, the resistance of dilute sulphuric acid is a million times, and that of solution of sulphate of copper, ten million times greater than that of pure silver. The resistance of pure water is very much greater than either of these.* The specific resistance of pure metals goes on increasing continuously as the temperature rises. At the melting point there is a sudden rise in the resistance, except in the cases of bismuth and antimony, which manifest a decrease of resistance at the melting point The sudden rise in the resistance referred to is in harmony with the supposition that intermolecular motions are much more considerable in the liquid state than in the non-cellular solid state ;( also with the conclusion, which we shall subsequently endeavour to establish, that heat increases molecule destruction, and therefore molecular motions in metals (see p. 318). As to the two exceptions we have mentioned, we suppose that the solid state of these metals is the cellular solid state, and that matter which is in this state is traversed by rigorous wave vibrations, which hinder conduction (see p. 70). And this view is seen to be in harmony with the fact that, as a general rule, metals manifest more resistance in the hard From Deschanel's ' ' Electricity,' ' edited by Prof. Everett, p. 670. f See p. 29. ELECTRICAL EBSISTANCE. 153 than in the soft state, the hardening being, it is suggested, an indication of a change towards the cellular solid state. Thus, tempering steel increases its resistance considerably, but subsequent heating and gradual cooling reduce the resistance again. It is interesting to notice that alloys generally have a greater resistance than that of either of their components, and particularly that there are four metals, lead, tin, cadmium, and zinc, the admixture of ever so small a quantity of which with other metals greatly increases their resistance. A very small percentage of another even worse conduct- ing metal raises the conductivity of mercury, but the addition of a larger quantity lowers the conductivity. The fact that slight impurities greatly deteriorate con- ductivity, especially shown by the case of copper, which often has its resistance increased by impurities to the extent of 50 or even 100 per cent., is, it is suggested, due to the impurities producing a change towards the cellular solid state. The co-efficient of resistance of the material of a wire is increased when it is stretched by a weight. Magnetization is sometimes found to affect resistance. Finally, the variations of resistance of selenium, which have furnished such important results in some modern applications of electrical force, are very suggestive. Thus in an amorphous state, which, we suppose, is an example of the cellular solid state, selenium has its lowest specific gravity, 4 '3, and in this state it is found to be a non- conductor. After continued heating, however, it passes into a crystalline state, which we suppose to be also a cellular solid state, but having its cells formed by the expansion of different atoms from those expanding in the former state. In this state its specific gravity is about 4'80, and it conducts, but the conditions of equilibrium of 154 NEW THEORY OF ELECTRICITY. its molecules are now so nicely balanced that the slightest changes of temperature, or exposure to light, produce changes in its electrical resistance, indicative, doubtless, of molecular changes. The theory of the producing causes of resistance, sug- gested above, may be summarized as follows : (1). Resistance is the direct result of the symmetrical intermixture of the opposite ethers in a current. (2). This intermixture is facilitated by any intermole- cular motions which break ether continuity, and thus hinder the progress of the ethers of the current. (3). Such intermolecular motions are considerable in liquids, as shown by their mobility, and in substances in the cellular solid state, because of the varying elasticity of their particles, and of the presence of cells filled with partly expanded ether. (4). Any cause which increases molecule destruction within bodies, or effects any other molecular change tending to disturb the continuity of their particles, in- creases resistance. Ohm's Law. The difference of potential at the two extremities of a given uniform conductor, is shown experimentally to bear a practically constant ratio to the strength of current passing, so that if E stands for this difference i.e., for electromotive force and c for the strength of current; = some constant R, the value of which depends on the dimensions and material of the conductor, and is, according to the above arguments, a measure of the ether-intermixing power of the given conductor. The relation expressed by this equation, in which R may thus be regarded as the resistance, is called Ohms law. The following experimental proofs of Ohm's law have been given by Pouillet. OHM'S LAW. 155 1. For thermo-electric currents he employed two thermo- electric elements, each consisting of a stout cylinder of bismuth with its ends turned down and soldered to copper wires. The two elements were arranged side by side, and the junctions at one end were immersed in hot water, those at the other end being kept in melting ice. The hot and cold junctions of the one were connected by a wire which was carried round a galvanometer needle. * Those of the other were connected by a wire ten times as long, which made ten times as many turns round the same needle in the opposite direction, so that the two currents opposed each other in their action on the needle. It was found that the needle remained at zero, showing that the current in the short wire was ten times as strong as the other, for one of its convolutions was able to balance ten convolutions of the other. Now the bismuth portions being identical in the two circuits, and so large as to give an effect compared with which the current-producing effect of the copper wire is inconsiderable, it is evident that the difference of potential at the two extremes of the wire portion of each circuit, i.e., the electromotive force E in this portion, was practically the same in both cases, and therefore, taking the fall of potential to be uniform in each wire, that the difference of potential between the extremes of a portion of TT the long wire equal to the short, must be ^. Therefore, taking the strength of current in the short wire to be c, and consequently, according to the above experiment, that o in the long wire ^, we have, for the same conductor, E -rji varies as c, that is ~ = some constant R. 2. For voltaic currents, Pouillet first sent the current of a battery through a galvanometer without any interposed * The principle of the galvanometer is referred to further on. < '-^' 156 NEW THEORY OF ELECTRICITY. resistance, and observed the strength of current, c. He then introduced, successively, known lengths of uniform wire h, 1 2 , 1 3 , and observed the currents obtained. Denoting these by G 19 C 2 , Cg, and taking x to denote the length of wire which would be equivalent to the unknown resistance of the original circuit, consisting only of the battery and the galvanometer, c _x + li c _x+ 1 2 c _x + l z C 1 ~ x 3 ~~ x C 3 ~ x From any of these three equations x can be determined, and Ohm's law is verified by similar reasoning to that used in the previous case, if they all give the same value of x. This Pouillet found to be substantially the case. * It is evident that the determination of the units of two out of the three of the entities of Ohm's equation will determine the unit of the third. In practice, the unit of c, the current has been determined that very commonly used is known as the electro-magnetic unit ; and the unit of resistance has also been determined by arbitrary reference to some particular conductor. The unit of the third, the electromotive force, has been deduced from the other two. It has been found that if different wires of the same material are inserted in a circuit which is taken through the coil of a galvanometer, it is necessary, in order to produce no change in the deflection, for the length of the wire used to vary directly as the area of its cross section. If, as we have supposed to be practically true, the resistance of a uniform conductor varies as its length, it follows from this that the resistance also varies inversely as the area of the cross section, a relation which would justify a comparison between the carrying capacity of a uniform conductor, and that of a pipe carrying water or other * See Deschanel's "Electricity," edited by Prof. Everett, p. 667. OHM'S LAW. liquid. It has been experimentally ascertained, that when several wires of the same length and material are arranged side by side, and thus all simultaneously introduced into a circuit, the resistance of the whole is the same as that of one wire of the same length and material, and whose section is the sum of the sections of such wires. We gather from the foregoing the following conclusions as to electric currents. (1). Since the moving ethers, are drawn, as we have concluded, chiefly from the body of mixed unmolecular ethers present in the circuit, the quantities of unmixed positive ether and unmixed negative ether moving in the circuit are practically equal. (2). For any such relation as that of Ohm's law to subsist in a uniform conductor, the current strength in different parts of it must be practically the same, notwith- standing the differences in the proportions of the two ethers at different places, which we have concluded subsist. The sum of the two ethers present at any moment irrespec- tive of their proportions is, it is evident, practically uniform in all equal portions of such a conductor, according to the above theories of the nature of a current. (3). The fact that the resistance of a uniform conductor varies inversely as the area of its cross section appears to indicate that all parts of the interior of the conductor are equally traversed by the moving ethers, and that the unmixed ethers are not confined to the surface as in the case of statical electrification. (4). The conclusion that for conduction to take place we must have ether continuity (p. 66) requires us to suppose that each moving ether is disposed in a layer longitudinally continuous, or in continuous longitudinal bands, each ether occupying its own portion of the conductor much in the same way, to use a rough illustration, as currents of distinct bodies of water of different temperatures are sometimes 158 NEW THEORY OF ELECTRICITY. found in the ocean in contiguity to each other, but unmixed, travelling in opposite directions or, at least, at different rates. (5). Since the space allotted to the unmolecular ethers in a given metal wire is practically the same, whatever the strength of the current passing through it,* we conclude that the quantity of each unmixed ether present in such a wire at any moment is the same for different strengths of current, and therefore, since, as we have argued (see p. 128), strength of current is determined by the quantity of the two ethers passing a given point in unit of time, that the velocity of t/ie ethers moving in the wire is proportional to the strength of the current; that the conditions are, in fact, similar to those obtaining when water passes through a pipe of given diameter, the quantity passing a given point in unit of time being a measure of the velocity. (6). If different lengths of a given metal wire experience a like electromotive force, i.e., have the same amounts of elec- tric potential at their extremities^ as in the case of Pouillet's experiments above referred to (p. 155) we conclude that the quantity and proportion of the two moving ethers contained at any instant within equal transverse elements (thin transverse slices) taken at corresponding ends of the different lengths of conductor will be the same in all cases.t (7). It follows that, when different lengths of the same conducting wire thus experience a like electromotive force, the quantity of ethers intermixed between the extremes in unit of time (if we neglect any ethers liberated by molecule destruction in the conductor) varies as the velocity of the moving ethers, which in this case, according to (5) above, varies as c the strength of current. * We do not here refer to currents strong enough to produce sensible molecular change in the conductor. f The difference between the quantities of the two ethers present at any instant in a unit element at any point in the conductor may indeed be taken to express the value of the electric potential at this point. OHM'S LAW. 159 (8). As (a). It follows from (7) that the quantity Q of ethers intermixed in equal portions of these similar conductors of different lengths, i.e., in portions in which the resistance is constant, when such con- ductors experience a like electromotive force, varies as - (I being the variable length of the whole wire taken), and therefore varies as C 2 , since c varies as j (see p. 155). (6). If different lengths of a similar wire conductor receive like currents c, the quantity of ethers inter- mixed between the extremes in unit of time varies as Z, and this varies as R. (c). With a given conductor and a given current the quantity of ethers intermixed varies as t, the time taken. It follows, combining these three conclusions, and choosing suitable units, that Q the quantity of ethers intermixed in a conductor = B c 2 t* The consideration of the heating effects produced in a conductor by currents of electricity is deferred till we reach the subject of heat. * This, as will be noticed subsequently (p. 320), is the expression found experimentally by Joule to be the value of the heat evolved. 160 CHAPTER XIV. ELECTRO-DYNAMICS Continued. Induction of Currents Attraction and Repulsion of Currents. WE will now pass to the consideration of two very important classes of phenomena connected with con- tinuous currents, namely, 1. Their power of induction, or of setting up other electric currents, discovered by Faraday ; and 2. The mechanical action of currents on each other, especially in producing movements in the conductors which carry them. A very great importance attaches to these considera- tions because, as we shall presently conclude, they furnish valuable elucidation of the origin of magnetic force. First, we will endeavour to place in the light of the foregoing theories Faraday's remarkable discovery of the induction of electric currents. The results which he arrived at are thus summed up in Prof. Crystal's Article on " Electricity" in the "Encyclo- paedia Britannica," to which we have so frequently referred in these pages. " Let there be two linear circuits, A B K E (the primary) and c D G (the secondary), two portions of which, A B and c D, are parallel, and near each other. " (a) When a current is started in A B, a transient current flows through c D in the opposite direction to the current in A B ; when the current in A B is steady, no current in c D can be detected ; when the current in A B is stopped, INDUCTION OF CURRENTS. 161 a transient current flows through c D in the same direction as the current in A B. These currents in c D are said to be induced, and may be called inverse and direct currents respectively, the reference being to the direction of the primary. Both inverse and direct currents last for a very short time, and the quantity of electricity which passes in each of them is the same. " (b) If the circuit A B, in which a steady current is flowing, be caused to approach c D, an inverse current is thereby induced in CD; when the circuit A B, under similar circumstances, recedes from C D, a direct current is induced in C D. We have already mentioned that when A B is at rest, and the current in it does not vary, there is no current in c D. A B has been supposed to approach and recede from c D ; but the same statement applies when c D approaches and recedes from A B. " (c) When a magnet is magnetized or demagnetized in the neighbourhood of a circuit, or approaches or recedes from the circuit, the effect is the same as if an equivalent * current approached or receded from the circuit. For example, imagine a small circular circuit placed hori- zontally, and a vertical bar magnet lowered in the axis of the circuit, with its north pole pointing down upon the circuit, the magnet may be replaced by a series of co-axial circular currents, and the motion will induce a current passing round the circuit against the hands of a watch."f We shall at present deal only with the two methods of producing induced currents marked (a) and (b) y leaving the third, marked (c), to be considered when we are dealing with the subject of magnetism. Of (a) the follow- ing explanation is offered. According to the theory of electric currents which has been submitted, both positive and negative ethers, which * Equivalent in the sense of producing the same magnetic field. t "Enc. Brit./' Art. ''Electricity," p. 75. 11 162 NEW THEORY OF ELECTRICITY. before the commencement of a current were quiescent in a conductor, and satisfying one another electrically, become, when the current is started, disentangled, as it were, and put in motion, the positive ether in one direction, the negative in the opposite. Now, each con- tinuous stream of ether thus produced will occupy some time, however short, in extending along the conductor when the start takes place ; and therefore, at the instant of the starting of a current, before the flow has become practically uniform from end to end of the conductor, we must picture a wave of each ether as flooding the con- ductor like a tidal wave, that of positive ether moving from one end, and that of negative ether from the oppo- site. We may suppose the travelling of a steep gradient of potential in this way to be equivalent to the passage of a body containing an electric charge along the path of the current ; and if, therefore, an unelectrified conductor is in proximity to the current when it starts, we may conclude that electrical induction (p. 94) will cause an aggre- gation, or heaping up, of the other ether on this conductor, opposite each of the moving steep gradients of potential of the two ethers travelling along the conductor in which the current is started. We have shown, therefore, that in the conductor not directly electrified there will, probably, be a steep gradient of negative ether moving abreast of the steep gradient of positive ether which initiates the current in the other conductor, and a corresponding steep gradient of positive ether moving in the opposite direction, abreast of the steep gradient of negative ether, which also initiates the current. Thus we account for the setting up of an induced inverse current in a secondary circuit, as stated in (). As the ebbing away of the streams of moving ethers at the cessation of a current may be similarly argued to INDUCTION OF CURRENTS. 163 produce moving gradients of fall of potential, direct induced currents, referred to in (a), will have a very similar explanation. As we should expect, sudden increase in a current, or sudden decrease, is productive of induced currents sudden increase in the primary current producing a momentary current in the secondary circuit in the opposite direction, and sudden decrease, a current in such circuit in the same direction as that of the primary current Next, as to the method of induction, marked (b). The fact that the "attracting" force subsisting between an electrified body and an unelectrified, or oppositely electrified body, varies as the inverse square of the distance, has been referred to the diminished density of the ether radiating from the charged body, in a direction away from it. Applying this to the case of a conductor carrying an electric current moved suddenly towards another con- ductor, we conclude that as the conductors approach each other, the effect of the ether radiations from the currents in the one on the unmolecular ethers in the other increases, and, moreover, that from the nature of the law just referred to, the increase is more rapid the nearer a part observed of the second conductor is to the conductor carrying the current. The effect observed may, it is suggested, be attributed to a steepening of electric potential in the second con- ductor, which is more rapid towards one end of this conductor than towards the other ; but the matter is diffi- cult to trace precisely. The reasonableness of the view of the origin of the inductive effect marked (b), just suggested, probably appears more evident from a consideration of the experi- ment by which the effect is usually shown. A long coil of wire, whose extremities are connected with a galvano- 164 NEW THEORY OF ELECTRICITY. meter, is so wound as to take the shape of a hollow cylinder, so that another smaller similar coil can be intro- duced into its interior. A current is passed through the smaller coil, and, while this is passing, it is suddenly passed into the centre of the larger coil, whereupon the galvanometer is found to indicate an inverse current in the latter. Conversely, when the smaller coil is with- drawn, a direct current in the larger coil is indicated. Faraday has proved experimentally that the insertion of any dieletric, or of any conductor which is not a strongly magnetic body between the primary and secondary coils Tfl -g-p- = sine of the angle B D E, therefore = sine of the angle of incidence ; And ^-rr-= p = sine of the angle DBF, therefore = sine of the angle of refraction. Therefore B E : D H : : sine of the angle of incidence : sine of the angle of refraction. Again, A D, the hypothenuse, is greater than A E, a side of the right-angled triangle A D E. And similarly c F is greater than c B, and c H is greater than c F. Much more then is c H greater than c B. Now, the velocity of light in A B or A D : the velocity in B c or D c : : sine of the angle of incidence : sine of the angle of refraction, which as we have seen above : : B E : D H. Consequently light will travel from E to B in the same time that it will travel from D to H. But we have shown that A E is less than A D. Therefore light will travel from A to B in less time than it will travel from A to H through D. We have further shown that B c is less than H c. Much more, therefore, will light travel from A to C through B in less time than it will travel from A to C through D. If D be taken on the other side of B, as at D 1? a perpen- 216 NEW THEORY OF LIGHT. dicular will have to be drawn to A B at B, and another to B c through D 1? and a somewhat different arrangement of lines will be presented, but similar reasoning will prove our proposition. If D be taken somewhere in the surface between the media out of the plane of incidence, as at D 2 , and we draw from it a perpendicular to the plane of incidence meeting it in D, it will at once appear that the lines A D 2 , c D 2 , being hypothenuses of right-angled triangles, are respectively greater than A D, c D, which are the sides, and therefore, that this cannot be a course travelled in least time. Thus, then, we have established that light travelling from A to c, or from c to A, will accomplish the journey in less time if it passes through B, than if it passes through any other point in the plane surface bounding the two media. The above is an elementary proof of the principle of least time where the surface of the more refracting medium is a plane. If the surface is spherical, the same principle* may be deduced from the following considerations. If in the above diagram the section of the surface between the media be indicated by a circle touching BD in B, and lines A D 2 , A D 3 be drawn to two points upon it equidistant from, and very near to B, the deduction from, or additions to the time of passage of light travelling from A to c through D 2 and D 3 respectively, which result from the surface on which D 2 and D 3 are taken, being curved instead of plane will approach equality the nearer D 2 and D 3 are taken to B. It follows, therefore, that the increment, or decrement, in the time of passage of light from A to c through points near B resulting from the surface being curved instead of plane, may be regarded as similar on both sides of B for very small distances from it ; * Sometimes, however, as we have stated, the course taken by the ray occupies a maximum instead of a minimum of time. REFRACTION. 217 or, in other words, that the time of passage from A to c through B will continue a minimum, or will become a maximum. And since small areas of any surface whatever may, so far as the application of the above arguments is concerned, be regarded as plane or spherical, it follows therefore that the above proposition is true generally. Corollary 3. If we take the same media, but reverse the direction of the ray of light, so that the incident ray shall be equal but precisely opposite in direction to the former refracted ray, the refracted ray will be equal and precisely opposite in direction to the former incident ray. For if in fig. 14 we suppose the direction of the ether waves reversed, the former direction of refraction being opposite to the present direction of incidence, the velocity of the former refracted ray will be equal to that of the present incident ray, we shall get a precisely converse result to that obtained above, the velocities and other quantities will correspond each to each in the two cases, and the direction of the ether waves after refraction will be opposite to that of the former incident waves. This is an instance of what is sometimes called the principle of reversibility, a principle which is generally found to apply to optical phenomena. It has been already intimated that the theory of refraction contained in these pages will be made use of to assist in building up a theory of reflection at the surfaces of transparent bodies, and, preparatory to this, before leaving the subject of refraction, let us compare two sections of the prism-shaped surfaces of maximum ether condensation in a group of ether waves taken at right angles to their axes, one made before refraction commences, and the other immediately after it is com- pleted ; and we will take the case of a ray of light passing into an isotropic more- refracting medium. 218 NEW THEORY OF LIGHT. Let fig. 16 represent the section of some of the prism- shaped surfaces of maximum ether condensation and of the prism axes of a group of waves before refraction. Then, if we suppose that the refraction takes place in a direction horizontal in our diagram (that is to say, if the plane of incidence intersects the plane of our diagram at right angles in a horizontal line), it is evident the relative position of the intersections of the refracted prism axes with a plane at right angles to the course of the waves will be found by projecting the intersections of the incident prism axes (lettered A in fig. 16) by means of perpendiculars to the plane of the diagram drawn O X Fig. 16. Fig. 17. through these intersections to meet a plane cutting this plane in a vertical line (as oy), and inclined to it at an angle whose cosine is the ratio of the cosine of the angle of incidence to the cosine of the angle of refraction. And we shall obtain the result of such a projection if taking the vertical line o y and a horizontal line o x, as axes, we set out points corresponding to the points (A) in fig. 16, having the same vertical distances from the axis o x, and distances from the axis o y which are to the horizontal distances of these points from this axis in the ratio of the cosine of the angle of refraction to the cosine of the angle of incidence. The relative arrangement of points (A') thus derived is shown in fig. 17. REFRACTION. 219 The prism-shaped surfaces of maximum ether condensa- tion will, as before, bisect at right angles lines joining the several intersections of the prism axes, and are depicted in fig. 17. If a ray passes through a refracting medium whose boundaries are parallel planes, it is evident from the foregoing conclusions not only that, as shown by expe- rience, the ray will have its original direction after it leaves the refracting medium, but that the prism axes of its waves will have the same relative situation, and the prism-shaped surfaces the same form as in the ray before it entered this medium. The waves will, however, we shall argue, have undergone some wasting and other modifying changes, to which reference is made hereafter. We shall revert again to the subject of refraction presently. 220 CHAPTER XX. REFLECTION OF LIGHT AND FURTHER CONSIDERATION OF REFRACTION. TTEEPING the conclusions just reached in mind, we **- will now proceed to consider the subject of the reflection of light. If a very elastic body is projected against a resisting plane surface, it is driven back from it along a line inclined to a perpendicular upon the surface at an angle approximating to that made by the direction of projection with this perpendicular,* and it is evident that the particles of elastic ether will have this property, and further, that the approximation to equality of the angles will in this case be very close indeed, owing to the freedom of movement which the ether particles possess. If, therefore, the particles radiating from a centre of condensation strike a reflecting plane surface, they will be repelled from it along lines which, if produced, will intersect in a centre situated behind the reflecting surface, whose position relatively to this surface is symmetrical with the position of the radiating centre. Thus, if in the accompanying diagram (fig. 18), A is a point in a prism axis from which particles are being radiated upon the surface BC, the point D lying in the * We have a familiar instance of this in the reflection of billiard balls from the cushions of a billiard table, the motions being so perfectly reliable, that experience enables a skilful player to accom- plish marvellous feats of dexterity. KEFLECTION OF LIGHT. 221 normal drawn through A, and equidistant from the surface B c, will be the point in whicn the paths of the reflected particles, produced through the surface, intersect each other, and these reflected particles will act precisely as though they proceeded from a centre at D, similar to the actual centre at A. It follows that the moving particles of a group of ether waves reflected from a plane surface, and the prism-shaped surfaces they produce, have the same courses and situations relatively to the plane of the surface on one side of it, as the same particles and the prism-shaped surfaces produced would have had to this plane on the other side of it, if the waves had not been intercepted, but had continued in the path of their incidence. And this involves the well-known law of reflection, that the angle of incidence equals the angle of reflection. As to the form and qualities requisite in a surface that reflection of light may occur, we observe That, since our arguments go to show that for ether waves to produce the sensation of light they must have the regularity of structure we have endeavoured to describe, it would seem that, for a surface to reflect light, it must consist of a number of true planes each of sufficient magnitude to reflect without distortion a considerable number of the synchronous vibrations associated in a single group of waves ; for the prism-shaped surfaces in a group of waves will not have the same form after reflection as before unless the reflecting surface is plane. This, however, appears at first to involve a contradiction, for if the surfaces of all masses of molecules are being continually eaten away through the successive explosion 222 NEW THEORY OF LIGHT. and return to the state of unmolecular ethers of the atoms composing them, all such surfaces will necessarily be rough when very small portions are considered, and not smooth as just supposed, and besides, as a matter of experience, all or nearly all surfaces however rough do reflect light. The reconcilement of this apparent contradiction is found in the conclusion already reached that at all free molecular surfaces layers of highly-condensed unmolecular ethers are present (see p. 50), for we see at once that this involves the filling up of hollows in the surface of the molecular mass with highly-condensed unmolecular ethers, and, if we suppose that reflection takes place from the stratum of ethers of high density, and not from the actual molecular boundary, we have a dense surface provided entirely free from abrupt irregularities when regarded with sufficient minuteness, and which may therefore be considered as made up of true planes more or less minute. According to this view the difference between reflection from a surface which we account rough, and that from a surface which we perceive to be smooth, is, that in the case of the rough surface, the planes composing it are very minute and inclined at all conceivable angles, so that the various groups of reflected waves pass in every conceivable direction, while in the case of the smooth surface these planes are nearly coincident in direction over com- paratively large areas, so that groups of waves having the same direction before reflection, if they strike the surface nearly at the same point, have nearly the same direction after reflection. In the case of diffused light i.e., light reflected from a rough surface and which passes indifferently in all directions the planes from which the reflections occur are commonly so minute as to make it impossible to trace EEFLECTION OF LIGHT. 223 them, but in some cases, as in that of powdered glass or snow, the origin of the surface assures us that it consists of innumerable small planes inclined at various angles. It is a familiar fact that for a solid surface to possess high reflecting power it must either naturally, as in the case of crystals, or through artificial treatment be smooth or polished ; the surfaces of liquids, through the operation of the laws of gravitation and capillary action, always tend to assume the molecularly even condition necessary for con- siderable reflection. Although slight disturbing forces produce broken reflec- tion at the surfaces of liquids, we notice that neither in solids nor liquids do the minute tremors and fluctuations, which we have concluded are continually passing through all masses of molecules, interfere with their reflection. Thus, although, as we have concluded (p. 70), the atoms at the reflecting surface of a sheet of glass, as well as all the other atoms composing the glass, are in a continual state of movement, it is a movement which is quite unbetrayed by the reflection. The explanation which naturally suggests itself is that the adherent unmolecular ethers have such freedom of movement that the actual molecular surface can undergo minute fluctuation without perceptibly impairing the truth of the reflecting surface of unmolecular ethers lying above it ; and such a facility of ether movement as this supposes has already been pictured in connection with our theory of electrical conduction. Another condition requisite in a surface that it may have good reflecting power is comparative rigidity, for, if the particles of ether which compose it readily take up the motions of the ether waves impinging upon them, it is manifest that, to the extent they do so, transmission and not reflection of these motions will be the result ; we want for good reflection a surface which presents an impenetrable 224 NEW THEORY OF LIGHT. wall to ether motions, turning them back as a breakwater turns back waves of water. This harmonizes with the fact that the metals, especially in a solid condition, are the best reflectors, their density indicating a closeness of texture which prevents their ether particles from at all readily taking up the wave vibrations of the unmolecular ethers. The reason why many substances of a cry stalline texture, whose hardness we suppose indicates that some of their atoms are even more condensed than those of the hardest metals, have but indifferent reflecting power as compared with metals, would appear to be that, as already argued, their structure is cellular ; so that ether motions are readily transmitted from the partly expanded ether of one cell- interior to the partly expanded ether of another cell-interior through the flexible cell walls. * It is a familiar fact that reflection is greater when light falls very obliquely, so that, although when we look into the waters of a still pond at our feet we may be able to see the swift motions of the fish, and even count the pebbles at the bottom, if we raise our eyes the trees and sky and grasses on the further bank are faithfully mirrored as in a sheet of silver. The explanation in this and kindred instances appears to lie chiefly in the well-known fact, that elastic surfaces, in all cases, have more power to repel a body when it falls obliquely than when it falls perpendicularly upon them, instances indeed being known where a moving body falling very obliquely is reflected, and retains considerable velocity, when, if it had fallen more directly, it would have pene- trated the opposing substance. f * We shall find this an important conclusion in explaining the transparency of crystalline bodies. t For example, persons have been injured by bullets discharged at waterfowl, which have struck the water very obliquely and been reflected from its surface . REFLECTION OF LIGHT. 225 Such an explanation does not however cover all the ground, indeed it is evidently inapplicable to the case of increased reflection produced as light falls more and more obliquely on the surface of a less-refracting medium ; the line of argument which follows will, it is believed, adequately deal with all cases for which the above explanation is inadequate. We will now, with the aid of the conclusions already reached as to the causes of refraction, proceed to investi- gate cases in which reflection is associated with considerable transmission. There is, perhaps, little difficulty in conceiving that molecules may be so condensed and closely aggregated as to oppose an effectual barrier to the transmission of the vibrations of the ether waves that they may be rigid enough to produce that elastic repulsion of the ether particles which constitutes reflection and the existence of the metals with their brilliant powers of reflecting seems to justify this view ; but what are we to say when we find a molecular substance so constituted as to afford great facility for the transmission of light, and at the same time evincing considerable reflecting power ; and that, not only with regard to rays which strike its surface externally as they come to it from a less-refracting medium, but also with regard to the same, or other rays when they strike the surface internally as they pass into a less-refracting medium from within the substance ; reflection being indeed in this case often more considerable ? Are we to suppose that some kinds of the atoms which compose the reflecting substance are pervious, while the rest are impervious to the ether motions of the incident waves; and, if so, how are we to account for the preservation of symmetry of both reflected and transmitted vibrations, evidenced by their light-producing power ? And, further, how will such a supposition at all account for internal 15 226 NEW THEORY OF LIGHT. reflection at the surface of a refracting medium when the ray in its incidence is passing towards the less-refracting substance? Evidently some other explanation must be sought. Let us consider first the case of reflection occurring when light parses into a transparent more-refracting medium. We have concluded that refraction is due to the ether motions having a less velocity in a more-refracting medium than in a less-refracting medium, and it follows that when the particles of ether radiating from any centre of con- densation in an ether wave pass a molecular boundary into a more-refracting medium they will experience a sudden check and some only of them will pursue their course.* Further the ether particles thus checked will accumulate, or be condensed, at the surface of the more-refracting medium, and in this way produce, for the moment, a layer of highly condensed unmolecular ether, and if this layer, like the layers of condensed unmolecular ether which we have concluded are attached to molecular surfaces, is capable of reflecting ether particles, each fluctuation as it strikes the more-refracting medium will thus furnish its own reflecting surface from which some of its particles will be reflected. And, finally, the same proportion of particles being reflected in the same manner in each similar fluctuation, both the portion of the waves transmitted and the portion reflected will have the unbroken symmetry which we have argued is a necessary characteristic of ether waves if they are to produce light. We have therefore a feasible explanation of this case. * To use a rough illustration it will be as when a stream of water, is partially dammed back by some obstacle, so that while it arrives at the obstacle at the rate of so many gallons per second, it passes off by the proper channel at some less rate. KEFLECTION OF LIGHT. 227 If we wish to ascertain in what way, if any, the re- flected and the transmitted waves will differ from ordinary waves we must carry our investigation further : In cases where the light strikes vertically, so that the prism-axes have the same relative situations after the refracting surface is passed as before, the proportion of each fluctuation turned back will be determined solely by the ratio of the respective velocities in the two media, and both the reflected and transmitted waves may be expected to be of the ordinary kind. But, when the light strikes the more-refracting medium obliquely, so that the prism- axes in the transmitted waves are found further apart (p. 218), the proportion reflected and the proportion transmitted of each fluctuation in a group of waves will be determined, not only by the ratio of the velocities, but also by the increase of the distances between the prism-axes the latter, by giving more time to each fluctuation entering the second medium before it encounters an adjoining fluctuation, producing increased capacity of transmission at the boundary between the media. And further, since in the latter case the distances between the prism-axes suffer the greatest increase in the direction of the plane of incidence, and no increase in a direction at right angles to this (p. 218), the portions of each fluctuation whose direction is nearest to that of the- plane of incidence will experience most of the increased capacity of transmission ; indeed generally the proportions of any given fluctuation transmitted and reflected will not be the same in all parts of it but will vary according to the direction of radiation of the ether particles observed. Next, as to the case of internal reflection, i.e., of reflec- tion as light passes into a transparent less-refracting medium. We see that in, this case there is no diminution of velocity when the fresh medium is entered, as there was in, y * ' , NEW THEORY OF LIGHT. the former case, but that when the light strikes obliquely there is a change which produces somewhat similar effects a diminution of the distances between the prism-axes which gives less time to each fluctuation before it encounters an adjoining fluctuation, and thus diminishes the capacity of transmission at the boundary between the media. And it is evident that, when this effect is greater than can be neutralized by the increased velocity, the particles of ether will experience a check, and each fluctua- tion as it seeks to pass out into the less-refracting medium will momentarily produce an aggregation of highly con- densed unmolecular ether which, like that produced in the former case, will, we may conclude, form a reflecting sur- face ; and such surfaces collectively will be more or less continuous according to the degree of contraction of the space for radiation allotted to each fluctuation which is thus produced. This, it is suggested, explains the increased reflection observed as light falls more and more obliquely on the surface of a less-refracting medium ; total reflection, to which reference will be made presently, occurring when the surfaces of condensed ether, produced as just explained, are sufficiently continuous. A similar argument to that on p. 227 may be used to show that the proportions of any given fluctuation trans- mitted and reflected in the case just considered will not be the same in all parts of it, but will vary somewhat according to the direction of radiation of the ether particles observed ; this conclusion, with the kindred conclusion previously reached in the case of refraction by a more- refracting medium, will presently be found important in explaining the phenomenon of polarization by reflection. Perhaps one of the best, as well as one of the most familiar instances of internal reflection presents itself when we approach a plate-glass window at night with a EEFLECTION OF LIGHT. lighted candle. On looking obliquely at the reflection of the candle in the glass we see several images one behind another, the greatest number being observed when the reflection is most oblique. The first and second of the series are the brightest, and of nearly equal intensity, and the rest have a regular gradation of diminishing intensity. This effect is analyzed in the accompanying diagram, in which A is supposed to be the position of the candle, B that of the observer. The portion of the direct rays from the candle (A) which Fig. 19. enters the glass experiences, when it reaches the further surface, partial internal reflection such as above described ; and in like manner the part thus reflected is in its turn partially reflected at the front surface of the glass, and so on ; the successive internal reflections forming zigzags between the two surfaces of the glass, along which rays of light pass whose intensity is less and less as portion after portion of them escapes. In the diagram the courses of the central rays con- cerned in producing three of the images are depicted. 230 NEW THEORY OF LIGHT. These courses are marked A m E, A n n n E, and Ap pppp E respectively. The first image is the result of one ex- ternal reflection, and its apparent position is a x ; the second is the result of one internal reflection and the accompanying refractions, and its apparent position is 2 ; the third is the result of three internal reflections and the accompanying refractions, and its apparent posi- tion is a 3 . The fact that the first and second images are about equal in intensity shows that the portion of the undimi- nished rays reflected from the external surface is only equal to the portion of the remainder reflected from the internal surface less that part of this portion withdrawn by in- ternal reflection at the anterior surface as the rays re-issue into the air, and therefore that the reflecting power of glass externally is less than it is internally when light falls, at a certain obliquity. If, instead of looking at the reflection of a candle from a window, as just explained, we look through the window obliquely at the candle, we see, as before, a series of images one behind another ; but the first will in this case be simply a refracted image ; the remaining images will be the results of reflection internally from the surfaces, as in the former case. When, instead of using a clear plate of glass as a reflector, we employ a mirror, we have a greater number of images because the mercury has immensely greater reflecting power ; and the second image which is pro- duced by the metallic surface is far the brightest, unless indeed the angle at which we look is so oblique as to very greatly reduce the transmitted rays by reflection at the outer surface. When we use a mirror all the reflections at the posterior surface are, according to the previous arguments, instances of reflection from the layer of highly condensed ether adherent to a molecular surface, not REFLECTION OF LIGHT. 231 instances of reflection due to restrained transmission as in the former case.* Before leaving the subject of internal reflection, just a few words must be said as to what is known as total re- flection. In the accompanying diagram (fig. 20), let A B represent the section of a plane surface between two different uniform media, the lower one being the more refracting medium, and let m up represent the section before and after refraction of the space between two adjacent prism-shaped surfaces of maximum condensation in a group of waves which are passing from the more-refracting to the less-refracting medium. Then it is evident that the more obliquely the waves meet the surface A B, the more narrowed or flattened will Fig. 20 this space become after refraction, and, as already stated, the less will be the portion of each fluctuation transmitted, the greater the portion reflected ; and that if the waves fall very obliquely the space available for radiation from * From a consideration of the diagram (fig. 19), we see that no two images, seen as proposed, present the same view of the candle ; for, what we see is precisely equivalent to a row of precisely similar candles, that is, differing only in their diminished order of inten- sity, similarly placed one behind another ; and it is manifest that, in such a row, the further back a candle stands, the less of a side view and the more of a front view we obtain of it : and it is evident that the further removed the candle is from the reflecting surface the more closely the different views of it presented by the multiple images will resemble each other, the smaller will be their angles of separation at the eye of the observer, and the more they will overlap. From this we see that if, instead of a candle, we look at the reflection of aluminous body whose distance is very great, e.g., the 232 NEW THEORY OF LIGHT. each centre will become so contracted that the waves transmitted will be unable to preserve their individuality, and therefore unable to produce light, and thus that total reflection will ensue. This conclusion is justified by ex- perience. Instances of total reflection are enumerated in all the text books. One such, a favourite and most beautiful instance, is furnished by a jet of water projected horizon- tally, illuminated by a ray of light travelling in the same direction as and within the jet. In this case the light is, through repeated internal reflections, carried down with the water from its horizontal path, and the water kindles and sparkles like liquid fire.* The critical, or limiting angle, so called as being the angle at which total reflection commences, is usually stated to be that angle of incidence which, on applying the law of refraction before enunciated, gives the direction of the refracted ray as actually coincident with the surface be- tween the media ; in experience, however, as just intimated, no light is transmitted when the direction after refraction would very nearly coincide with the direction of the surface between the media. From the arguments which have been presented, as to moon, or a star, all the multiple images should practically coincide and appear as one image only. When, as sometimes happens, we see multiple images of the moon on looking through a plate-glass window, the effect arises from the glass not being perfectly homogeneous ; and, in accordance with this, it is found that the multiple images, when they occur, have various distances apart in different instances, and various positions with respect to the observer quite irrespective of the plane of reflection. It may be noticed that if it were not for the broken nature of the surface of the jet, due to the continual rearrangement of its particles (p. 5'2) and the presence of foreign particles within it, the rays of light would always strike the surface of the jet so as to be entirely subject to total reflection, and would therefore be invisible. REFLECTION OF LIGHT. 233 the cause of internal reflection, we arrive at the important conclusion that it is not necessary to have a sharply defined surface between two media for total reflection to occur in other words, that the increase of refracting power necessary to produce this phenomenon may be gradually and not suddenly reached ; the effect in this case partaking partly of the nature of refraction and partly of the nature of reflection. For, suppose rays to strike obliquely to the stratification of a medium made up of an indefinite number of thin layers of successively less- refractive power, so that the rays are gradually bent round as- they pass through the successive strata, and each refracted prism becomes more and more flattened. Evidently, in such a case, we should as before, at last reach a stratum at which the space available for radiation from each prism-axis becomes so contracted that no waves capable of producing light are transmitted, and thus, practically, the whole of the rays are reflected. The amount of refraction experienced by the incident rays in passing through a medium of increasing refractive power before reaching this totally-reflecting stratum will evidently be exactly counterbalanced by the reverse re- fraction similarly encountered by the reflected rays, so that here, as in ordinary total reflection, the law will hold that the angle of incidence equals the angle of reflection. To make the above clearer, see the accompanying diagram (fig. 21), in which a medium is supposed to have uniform refracting power from A to B, and then to decrease gradually in refracting power from B to C. A group of prisms, D, are represented as passing obliquely into this medium of graduated density, and as being, in consequence, when they pass below B B, gradually bent round towards the direction of stratification of the medium, so that they strike a stratum E E with sufficient obliquity for total re- 234* NEW THEORY OF LIGHT. flection to occur. The courses of the reflected prisms are shown as symmetrical to those of the incident prisms. An instance of total, or nearly total reflection occurring where there is no sharply defined boundary between media of differing refractive power appears to be found in the mirage, that strange often-described phenomenon in which parched and tenuous air closely mimics the appearance of extensive tracts of water, giving the most perfect reflection of sky, trees, and other objects.* The simplest form of mirage appears to be due to a level surface of greatly heated sand so heating the air next to it, that, although this heated air is continually rising and mixing with the cooler air above it, there is a steep gra- dation of increasing density upwards, which furnishes a medium that is more and more refracting in an upward direction. The fact that the trees and other objects seen in a mirage are frequently found to be hidden from view when the * Dr. Thomson, in his "Land and the Book," remarks that the name for mirage in Sanscrit means " the thirst of the antelope," and gives us his experience as follows : " I once gave chase to a flock of gazelles on the plain of Tireh, south-east of Aleppo. The day was intensely hot, and the antelopes made direct towards a vast mirage, which covered the whole eastern horizon. To me they seemed to be literally leaping through the water, and I could see their figures below the surface, and reversed, with the utmost dis- tinctness. No wonder they were deceived, for we, their pursuers, were utterly confounded." REFLECTION OF LIGHT. 235 phenomenon has passed, appears to be accounted for by refraction accompanying the reflection Under ordinary atmospheric conditions the objects are hidden from view by the nature of the ground, but the gradation of density in the air which produces reflection, and thus gives the appearance of water, produces also refraction, which bends the rays from objects situated below the line of sight, round the intervening rising ground, and thus apparently lifts the objects into view during the continuance of the mirage. The effect called looming, which is experienced in calms at sea, and by which shadowy inverted images of objects are seen immediately over the objects themselves, is explained in a similar manner, except that in this case the heated, and therefore less refracting air is above instead of below. We have not, in our consideration either of reflection or of refraction, treated of the phenomena produced by curved surfaces, and it does not come within the scope of this treatise to do so, because the various effects produced when reflecting or refracting surfaces are curved are all mathematically deducible from the plane effects, and do not throw any light upon the theories here put forward. We need only call the reader's attention, in passing, to the facts that all curved surfaces may be treated as made up of an indefinite number of very small plane surfaces placed at right-angles to the normals of the curved surfaces ; and that, in harmony with our conclusions as to the constancy of the shape of the prism-shaped surfaces of maximum condensation in the ether waves as long as their course is through the same medium, lenses or curved mirrors need not be supposed able to cause either convergence or diver- gence of these surfaces or of the prism-axes in any given group of ether waves, but merely to cause a larger or smaller number of groups to pass in particular directions. 236 NEW THEORY OF LIGHT. Thus, bringing rays to a focus is not to be regarded as a squeezing together into a small space of a number of ether waves, but as an increase of their number and frequency at some particular point. A few remarks as to how the structure of bodies regu- lates their relative transparency will be made when the suppression of rays of light in the course of their passage through bodies has been treated of. Our subsequent consideration of the subject of heat will throw light on the fact that refraction uniformly diminishes as temperature increases. We may remark, in closing this chapter, that where the colour of reflected rays differs from that of the incident rays which produce them, as in cases of diffused light coming from coloured substances, it has been shown that the cause is not any peculiarity of reflection, but lies in the suppression of some of the incident rays ; the cause of this suppression we shall endeavour to explain hereafter. 237 CHAPTER XXI. DISPERSION. THE origin of ether waves suggested in this treatise (p. 202) implies difference of scale in the vibrations of different series of waves, according to the kind of atoms setting up the waves by their explosion, and the nature of the ether conditions prevailing about these atoms when they explode ; * each group of waves, as we have argued, preserving its individual kind of vibration throughout, but succeeding groups generally presenting different kinds, except only when the light is monochromatic. We have hitherto considered ether waves without reference to their magnitude ; in the present chapter it is proposed to deal with phenomena which reveal a difference in scale, or magnitude of different waves. At the first glance, the glorious softly graduated succession of the seven rainbow colours known as the spectrum, resulting from the fan- like expansion of a ray of white light by a prism, naturally suggests the discri- mination of light into seven kinds having the seven different colours, or into some less number of kinds whose superposition, or combination in the spectrum, produces these seven colours ; but upon examination it is found that colour is a subordinate feature, f that the See further as to this, p. 242. t As to colour, see p. 257. 238 NEW THEORY OF LIGHT. analysis made by a prism is not a matter of colour tins depending merely on the effect on our senses* but a matter of degree of refranyibility. For, since the constancy of the effect produced shows that each separate kind of light is uniformly refracted, we see that light of any one kind only is not " dispersed," i.e., rendered more divergent by passage through the prism ; indeed this receives direct proof if a ray of mono- chromatic light issuing from a narrow slit is passed through a prism, the size of its image on a screen not being thereby appreciably increased. And the wide continuous band of illumination of the spectrum must therefore be regarded as made up of a large number of lines of light of the same magnitude as the narrow line of white light seen when the prism is withdrawn ; f each of these lines, whose combined effect gives continuous illumination from end to end of the visible spectrum, consisting of light of a In connection with this wonderfully beautiful phenomenon, the spectrum, we cannot refrain from reminding the reader that mere mathematical or mechanical conditions can in no case suffice to produce a sensation, but merely constitute the machinery which transmits or concentrates effects. Look at that band of gorgeous colours ! Theoretically, it is just a collection of ether waves similarly organized, but having some difference of scale. Actually, to the soul of man it is a ravishing harmony in his inner nature awakened by the touch of Nature's fingers. The pleasure, and the sense of beauty and fitness which we feel in beholding this or any other beautiful natural phenomenon are in no way accounted for by its mere mechanism; they are a separate creation foreseen and sympathized with by the great Creator, who must have experienced the pleasure before He endued His creatures with power to par- ticipate in it : " God saw that it was good." t A continuous spectrum, in which a thin line only of each kind of light is found, and overlapping of the different kinds avoided, is called a pure spectrum ; it can be obtained in several ways, but perhaps the simplest method is to use light passed through a fine slit. DISPERSION. 239 particular kind having its own characteristic degree of refrangibility by the prism.* As to the source of the difference in refrangibility of different kinds of light, it is suggested that the retarding effect, already explained, exercised by the atoms composing a refracting body on the ether motions of the waves which traverse it, is more considerable the more rapid these motions are ; because the slower and less frequently repeated the ether motions, the more the atoms can participate in them ; consequently that difference of refrangibility depends on difference in the time of pul- sation of the waves refracted waves whose pulsations are more rapid being more refracted, those whose pulsations are less rapid being less so.f The fact that the amount of dispersion a refracting body produces becomes less as its temperature in- creases, appears to be in harmony with this sugges- tion, for we shall argue hereafter that rise of tempera- ture indicates an increase in the quantity of unmolecular ethers present, and this would be likely to cause in- creased participation by the molecules in the more rapid We may here refer to the important fact that a dark con- tinuation of the spectrum is present in both directions beyond the visible bands of colour. In other words, there are ether waves to which the foregoing argument applies, having, some a greater, some a less refrangibility than the waves of light. The presence of those beyond the red end is manifested by their heat (see p. 309), that of those beyond the violet end by their production of fluorescence in certain bodies. These dark waves obey similar laws of refraction and reflection to those which rule the waves of light, and must therefore be regarded as of a precisely similar nature to the light waves ; a proof not only that the primary distinction between the waves has nothing to do with colour, but more than this, that it has nothing to do with light-producing power. f This is in harmony with the conclusion otherwise reached, that the shorter waves are found at the blue end of the spectrum, the longer at the red end. 240 NEW THEORY OF LIGHT. ether movements, involving lessened retardation of the shorter waves. Prisms formed of certain substances give spectra of abnormal dispersion, the colours being arranged so that, as to their order of succession, it appears as though opposite portions of two normal spectra were lying partly one over another. A curious experiment made by De Klerker in 1879 with one of these substances* is suggestive of the cause of the phenomenon. He employed two hollow prisms of equal angle, turned opposite ways, and filled with alcohol. Through such a combination light passes, as we know, without refraction or dispersion. When a few drops of a fuchsine solution were added to the contents of one of the prisms, the yellow, orange, and red rays (in the order named) began to separate themselves from the others. This process could be carried on until the solution was so strong that it transmitted no visible light. All this time the blue and violet rays remained apparently unre- fracted the yellow, orange, and red showing continually increasing refraction. The following, based on our hypo- thesis that the ether is of two kinds, seems a probable explanation. Since the fuchsine is added to the contents of one only of the prisms, and its addition produces refraction of the rays towards the red end of the spectrum only, it is evident that so far as the remaining rays are concerned, the presence of the fuchsine makes no alteration in refracting power ; and it would seem, therefore, that in the mixture we have a dual medium, one part of which, the fuchsine solution, transmits the rays towards the red end of the spectrum more readily than the rays towards the violet end while the remaining constituent, the alcohol, transmits all the rays with equal facility. Taken from " Enc. Brit.," Art. "Light," p. 602. DISPERSION. 241 In iodine vapour, which is one of the substances giving abnormal dispersion, it is noticeable that the dispersion is less as the temperature is higher. The phenomena of dispersion supply important evidence in support of our theory of the origin of ether waves, for, as we should expect from the foregoing arguments, the nature of the spectrum produced by a given prism is found to depend on the nature of the light source dispersion proves a revealer of secrets, and in telling us what particular waves produce a given ray, informs us of the nature of the molecules whose incandescence originates the waves. The disentangling, by the use of a prism, of the various combinations of waves which are concerned in producing the characteristic light of different incandescent bodies has become an important science, the science of Spectrum Analysis, and a separate chapter will be devoted to this subject after we have considered the subjects of Heat and Chemistry ; we may, however, mention here one or two. conspicuous facts. Perhaps the most significant is the fact that the spectrum of any one of the elements in a gaseous state, when incan-- descence has been produced in a certain way, consists of but a few narrow lines,* whose position is strictly charac- teristic of the element made use of, nearly all the terms of the continuous series composing a complete spectrum, being entirely absent. The natural explanation evidently is, that,, when the conditions obtaining are sufficiently simple, the explosions produced by each particular kind of primary atom in a given element are of precisely uniform violence, and have- uniform frequency in time and space, and so produce waves of one uniform time of pulsation characteristic of this particular kind of primary atom ; each kind of waves, having its own constant place in the spectrum. * In some few cases a thin bright line stands alone. 1,6, 242 NEW THEORY OF LIGHT. The complementary fact that greater condensation in the incandescent body gives a great variety of variously refrangible kinds of light covering large continuous tracts of the spectrum, or extending throughout it, also receives a natural explanation. For we see that when we have not the freeness and uniformity which, according to our arguments, prevail in the tenuous gaseous state, par- ticular primary atoms, instead of producing waves of uniform time of pulsation, may be expected to produce a variety of waves whose times of pulsation somewhat differ in different groups of waves, the result being that, instead of ether waves of a particular wave-length, we have waves presenting a continuous series of wave-lengths whose mean is some particular wave-length, covering continuous tracts of the spectrum of greater or less extent. Another important fact is that increased incandescence of a solid, or liquid body extends the tract it occupies in the spectrum in the direction of the violet end, the light emitted containing more and more refrangible rays as the incandescence increases. This was shown by Dr. Draper many years ago. He employed a voltaic current to heat a platinum wire, and studied by means of a prism the successive introduction of the colours of the spectrum. A familiar example of the fact, scarcely requiring the aid of a prism to prove it, is seen when we heat a poker ; for it rises from a black heat to a red heat, and from a red heat to a white heat. The explanation of this would appear to be that increased incandescence is simply increased frequency in time and space of atom explosions, so that its occurrence not only makes the number of the groups of waves which are successively produced greater, but also makes the distances between the centres of explosion in some of them less, giving waves with shorter time of pulsation, i.e., more refrangible waves. DISPERSION. 243 Finally, there is one other fact we will allude to here, which, besides confirming our conclusions from the other facts that have been mentioned, forms our first intro- duction to a very important effect of ether waves on one another, which will again and again, in various shapes, invite our attention in dealing further with the phenomena of light : In a pure spectrum of an incandescent body the other- wise continuous tract of various kinds of light presented is found, in cases where the incandescence is violent, to be intersected by dark lines more or less numerous, the well-known Frauenhofer's lines, first discovered in the spectrum of the sun by the observer of that name.* The position of these dark lines in the spectrum is precisely that of the bright lines which form the fragmentary spectrum of the incandescent body when in the state of vapour, and experiment has shown that the effect is due to a power possessed by the vapour of a substance of blotting out light of the particular kind this vapour would itself emit if incandescent. We see at once that the existence of Frauenhofer's lines in pure spectra confirms our previous conclusion, that the complete spectrum is made up of successive distinct terms, of which each is produced by groups of waves of one definite wave-length only, so that finely graduated as the series is, we should find, if our sensibility were delicate enough, that it consists of terms distinctly various in place and intermittent in production.! * As we shall notice hereafter, Frauenhofer's lines in the solar spectrum are considered to result from the blotting out, or, rather, weakening of certain rays through the intervention of a flaming atmosphere supposed to be present around the nucleus of the sun. f As already remarked, flashes of colour to be seen in the twinkling of some stars seem to illustrate our conception of distinct groups of ether waves of different kinds following one another in rapid succession. 244 NEW THEORY OF LIGHT. As to the way in which the lines are produced : If of the various kinds of waves passing through any given mass of vapour some have the wave-length of waves which would be produced by explosion of the atoms composing the vapour, it is evident that wherever these particular waves produce concerted atom explosion in the vapour, and thus set up ether pulsation synchronous with their own, an amalgamation of the ether pulsations of different origin thus coming together must be looked for ; and, except in cases where the one set of pulsations are so timed in relation to the other set as to produce merely an intensification of the vibration,* this will result in the production of modified waves having different refrangibility from their components, and, indeed, probably incapable of producing light, f And thus, in cases where the atom explosion produced in a vapour is considerable enough, a weakening or blotting out of particular wave-lengths will be manifest in the spectrum of light passed through this vapour. In harmony with this explanation, we suppose that it is not extinction but modification of certain waves which causes the dark breaks in the spectrum known as Frauen- hofer's lines. The occurrence in the path of ether waves of a com- paratively small amount of atom explosion productive of similar waves is adequate, it would appear, to modify the waves sufficiently to destroy their light, even in cases where the brilliancy of the incident light would indicate that groups of powerful waves are following one another with great rapidity. * See p. 248. f The sensation of light is hereafter argued to be due to atom explosion at the retina, and it is supposed that atoms liable to be exploded by the uncombined waves would not be similarly affected by the waves of shorter pulsation resulting from the amalgamation. DISPERSION. 245 The fact that a medium of incandescent vapour blots out from a continuous spectrum only the narrow lines of colour which belong to the spectrum of the light it emits, must be taken to indicate a necessity for complete identity of the rates of pulsation of two superimposed groups of waves, that they may amalgamate and form one modified group. The reason why the similar ether waves from two different sources of light, or from different points at the same source, when they happen to travel together, are not in the ordinary way mutually destructive of the power of producing light, appears to be that the travelling together of similar light from two different sources merely means an increase of the number of the groups of waves of a certain kind travelling in the given direction, and does not generally involve the amalgamation of one group with another. In closing these few remarks on dispersion, we observe that the explanation of the phenomenon which has been offered affords striking corroboration of the theory that each of the so-called elementary substances is an gation of particular kinds of primary atoms.* * See p. 19. 246 CHAPTER XXII. PRODUCTION OF IRIDESCENCE BY INTERFERENCE DIFFRAC- TION COLOUR PRODUCED BY THE PRESENCE OF DUST OR SMALL PARTICLES. fTlHE theory offered in the last chapter of the amalgama- - tion of two groups of the same kind of ether waves when they travel in the same direction and are super- imposed applies to what is known as interference, and some details of the theory come out with great clearness in con- nection with the phenomenon of iridescence attributed to this cause. If a drop of paraffin is placed upon the surface of water, the laws of attraction cause it to spread out into a very thin film (p. 53), and as the film diminishes in thickness gorgeous colours of different hues are successively dis- played. That these colours are not in any way peculiar to the materials employed, but are simply functions of the vary- ing thickness of the thin film, is proved by an experiment made by Newton, which furnishes an admirable analysis of the nature of the phenomenon. To get a film of variable, and, at the same time, calculable thickness he took a plano-convex glass lens of very feeble curvature, and laid upon it a plate of glass with a plane surface. He then found that the film of air between the lens and the glass plate furnished a characteristic system of colour arranged in concentric rings about the central point IRIDESCENCE. 247 of contact.* When he used monochromatic light a series of bright rings, separated by dark ones, was produced ; and he found that the thickness of the glass, measured succes- sively at each bright band of this series, gave a series of values in arithmetical progression, and that, taking successive series, the differences between succeeding terms, were less and less in passing along the spectrum from the red towards the violet in other words, that the rings and the dark spaces between them were narrower and yet narrower in the different series as the light selected had its place nearer the violet. Finally, add to these observations the fact that, travelling out from the centre, the film presently becomes too thick to produce any colour effect. The received theory of the colours of thin films is, that ether waves reflected from the upper surface of a film being followed by precisely similar waves reflected from its under-surface, the two sets of similar waves passing in the same direction, one upon the heels of the other, pro- duce interference and mutual extinction, in cases where the thickness of the film lias approximately a certain proportion, or a proportion which is some multiple of this, to the wave- length ; so that, when white light is employed, each parti- cular thickness extinguishes certain colours, and conse- quently shines with the colours complementary to these. This is evidently very much in harmony with the theory of the amalgamation of two groups of similar ether waves The experiment throws some light on the molecular structure of glass, for it is found that considerable pressure has to be exerted in bringing together the two pieces of glass to show a black spot in the centre of the rings, and this would seem to indicate that the surfaces are in such a molecularly vibratory condition, and, moreover, that the vibrations are so vigorous, that the two surfaces do not have con- tinuous contact until a considerable force has overcome the oscilla- tions of the vibrating particles (see p. 70). 248 NEW THEORY OF LIGHT. offered in the last chapter, and it is only necessary to suggest a slight amplification of the theory on one or two points. As already intimated, the waves which interfere are not to be regarded as destroying one another, but merely as amalgamating to produce new waves so modified as to be unable to produce light. The approximate equality in width of the light and dark rings in Newton's experiment points to the conclusion that of the different relative positions of the two sets of similar waves given by reflection at different points from the two surfaces of a film of graduated thickness, including all cases ranging from that of coincidence of rank of the two sets of waves to the case in which one set is exactly half a wave-length behind the other, about one half produce amalgamated waves in which the waves of one set join with those of the other to form united waves of similar wave-length of double strength, and the other half produce compound waves, in which the motions originating from one set continue to fall between those originating from the other. And lastly, the fact that interference occurs only when a film is very thin supports our conclusion that groups of waves of the same kind travelling in the same direction are successive, and not continuous ; the succession being a broken one, and group following group in inconceivably rapid succession. For, if this is so, we see that the waves of any particular group reflected from the second surface will not be superimposed on those reflected from the first unless they reach the last-named surface while the reflection of this group of waves from this surface is still going on. The iridescence of finely striated surfaces is very simi- larly explained. One of the best instances of it is presented by what are known as " Barton's buttons," articles once employed for ornament, whose faces are polished metal IRIDESCENCE. 249 stamped by a die of hardened steel, engraved with a pattern made up of small areas ruled in different directions with close equidistant parallel lines.* Let the accompanying diagram represent a highly magnified section of such a striated surface with its adhering stratum of condensed ether, from which we have concluded the reflection takes place (p. 222). The surface of this stratum will evidently be undulatory, and, selecting similarly placed points in each of the similar depressions shown upon our section, it is manifest we can draw a suc- cession of parallel normals inclined at any angle we please to the general direction of the surface ; this angle being regulated by the position of the similar points. And from these normals we can determine the direction of parallel Fig. 22. rays of light after reflection from the similarly situated points. Now, if the striation is sufficiently fine, the same iden- tical group of waves will suffer reflection in more than one of the furrows, and the waves reflected at any one of the similarly situated points will be slightly in advance of the waves of the same group reflected at the point next adjoin- ing on one side, and slightly behind those reflected at the point next adjoining on the other side ; this difference in rank will, moreover, be precisely regulated by the positions on the surface of the similarly situated points. The resem- blance to the conditions which we traced in the case of reflection from the two surfaces of thin films is evident, and the theory of interference already placed before the reader will we submit apply in the present case. Striated surfaces, such as just described, have been used Mother o' pearl has been proved to owe its play of colours to fine striations analogous to those of " Barton's buttons." 250 NEW THEORY OF LIGHT. for the purpose of calculating the actual wave-length of ether vibrations. Diffraction. The name " diffraction " has been applied to certain phenomena which we shall endeavour to show are due to the combined action of refraction and interference. Two typical instances will be dealt with. Diffraction bands are produced by allowing white light whose rays are all parallel as, for example, sunlight from a small portion of the sun's disc to pass through a very narrow straight slit ; a screen placed to intercept the rays Fig. 23. then displaying a rectangle of white light, much wider than the width of the slit, bordered on each side with coloured fringes, and the narrower the slit the wider this rectangle and the attendant fringes. If the light be mono- chromatic, we get a remarkable series of bright bands separated by dark spaces ; the central band being widest and by far the brightest, and those on each side of less and less brightness as we travel from the central band (see fig. 23). The extreme red end of the spectrum gives the widest bands separated by the widest dark spaces, and both the bands and the spaces are narrower the nearer the place of a selected colour is to the violet end of the spectrum. The central white rectangle with coloured DIFFKACTION. 251 fringes, produced when we use'--; , 256 - MEW THEORY OF LIGHT. and therefore we see that the greater contraction of the space allotted for transmission experienced by the more- refrangible waves, which has just been argued, will cause these waves to be transmitted in a less proportion than less refrangible waves, and consequently to be more reflected. The fact that the light transmitted through media containing small particles exhibiting the phenome- non just referred to is yellowish or reddish, like the transmitted colours of sunset, is consistent with this explanation. This closes our examination of the phenomena of colour due to the form and not to the composition of bodies. 257 CHAPTER XXIII. - COLOUR PHOSPHORESCENCE AND FLUORESCENCE TRANSPARENCY. TTTE propose to consider in the present chapter the various sources of the distinctive colours of bodies in other words the causes of the prevalence of waves of certain wave-lengths in the light coming from particular groups of atoms.* These sources are, it is submitted, three in number, viz. : 1. A greater facility of transmitting some ether waves than others possessed by some molecular masses, causing them to reflect larger proportions of the waves transmitted with less facility. 2. The modification and destruction, so far as light- giving power is concerned, of certain of the waves travers- ing a body, occurring through their amalgamation with similar waves set up by the explosion of some of the primary atoms composing the body, and this explosion being chiefly due to the action of the incident waves, t The colour of the body is in this case due to the unaltered incident waves, transmitted or reflected as the case may be. 3. Explosion of the atoms of a body considerable enough * Colour in its physiological aspect is considered subsequently. f So far as the waves set up are due directly to the action of the incident waves, this is the principle on which we have already explained Frauenhofer's lines. 17 258 NEW THEORY OF LIGHT. for the ether waves produced to determine directly the colour produced.* The first-mentioned of these is, it is suggested, the source of the distinctive colours of the various metals, the least transparent of all bodies. Thus the preponderance of yellow in light reflected from gold is probably due to the more ready penetration of this metal by light of the complementary colour ; and this is to some extent coun- tenanced by the fact that the transmitted colour of unbeaten gold is violet and of beaten gold green ; the matter is however obscure. The second source of colour which is above suggested we connect with the phenomenon ordinarily called absorp- tion ; a power which most substances possess of suppress- ing some particular kinds of light, so that the light they transmit when illuminated, whether that evidently passed through them, or that which is reflected after entering them to a greater or less depth, t is complementary of this suppressed light. It has been found that nearly all the objects around us owe their distinctive colours to this power of so-called absorption. The reason why, in cases of colour thus produced, the ether waves which suffer modification have so wide a range O of wave-length, and are not merely of the kind which the atoms of the body if exploding quite freely would produce, as in the case of Frauenhofer's lines, appears to be that the highly-condensed state of the atoms modifies their explosive effect, so that the waves they produce have a wide range of wave-length ; a suggestion which will receive abundant corroboration when we deal with the subject of Spectrum Analysis. * Colour thus produced will evidently be due solely to waves set up by the exploding atoms of the body which have not been deprived of light-producing power by amalgamation with incident waves. t The transparency, or penetrability of bodies by ether waves will be considered presently. COLOUR. 259 The supposition that some of the ether waves of the light falling upon a body produce atom explosion in it productive of similar waves, is in harmony with our pre- vious arguments, and further, as evidence of the occurrence of atom explosion in bodies exposed to light we have the following : (a) It is found that absorption is always accompanied by the liberation of heat, and heat will in the sequel be argued to be an evidence of molecule destruction (p. 309). (6) The phosphoroscope devised by Becquerel has shown that nearly all bodies shine with phosphorescent light for a shorter or longer time, sometimes but a mere fraction O ' of a second, after having been strongly illuminated ; a fact which, if, as we have argued, light results from atom explosion, proves that a condition of atom explosion is produced by the incidence of ether waves, and continues for a short time after their discontinuance.* (c) The gradual loss by bodies of their characteristic colour, so familiar to us as the fading of colour, and due to the survival of ether waves of kinds formerly " ab- sorbed," may probably in many cases be regarded as a wasting effect of the process of absorption, due to par- ticular kinds of atoms becoming gradually fewer at the surfaces exposed to the incidence of the illuminating waves ; f and it accords with this view that fading is more rapid the stronger the light. (d) The molecular changes produced by light, indicated by its destructive effect in rotting fabrics, we should suppose arise from molecule destruction. And molecule * Phosphorescence is considered further, p. 260, f Rapid alterations of colour must, however, be attributed to chemical changes. In living organisms, e.g., flowers, we may sur- mise that fading is prevented or retarded through fresh atoms being supplied by the circulatory changes incident to a state of life. 260 NEW THEORY OF LIGHT. destruction will in the sequel be argued to be the first step in the chemical changes produced by light. In connection with the above theory of absorption we may refer to the following familiar experiment as fur- nishing evidence that molecular masses when placed in conditions favourable to atom explosion emit ether waves of the kinds which our theory of absorption requires us to suppose they are ordinarily emitting, and as the result of the emission of which they have their characteristic colour. If we take a piece of stoneware of a black and white pattern, and heating it to redness view it in the dark, we find that the black of the pattern shines much more brightly than the white, so that a curious reversal of the pattern is produced. From this and other kindred experiments the law has been deduced that bodies when cold absorb the rays which they give out when hot* The third source of colour we have suggested is, it is submitted, the source of all cases of the emission of coloured light by molecular matter, including all forms of incan- descence, from that accompanying the violent chemical action of combustion to the softest electric glow, and also all instances of phosphorescence and fluorescence. Several facts relating to these different phenomena are in harmony with this theory. Thus the very fact that light so commonly accompanies combustion, viewed in connection with the arguments offered in the sequel that the heat and chemical change of combustion both result in all cases from the expansion An instance of this law as applied to ultra-red rays is found in the fact that if we pass the rays from heated rock-salt through a plate of cold rock-salt, this substance, which is generally found very transparent to rays at the extreme red end of the spectrum, "absorbs" a very large proportion of such rays, a moderately thick plate disposing of at least three-fourths of them. PHOSPHORESCENCE. 261 of atoms to the unmolecular state, favours this view as regards all cases of ether waves produced during com- bustion ; the fact already referred to, that the colour of incandescent vapour is quite characteristic, so that when analysed by a prism its ether waves are found to have certain definite places in the spectrum according to the kind of matter rendered incandescent, furnishes the strongest evidence in the same direction. And we may further cite, as giving some additional support, the fact that flames conduct electricity ; for we may suppose that in this case the ether continuity, which we have concluded is necessary that conduction of electricity may occur (p. 68), is due to the separation or assortment of newly-liberated ethers into continuous masses of each kind. Again, the fact that electricity, whose power of pro- ducing the destruction of primary atoms has been already referred to (p. 122), commonly produces light when denied free conduction, goes far to justify the reference of all light electrically produced to the explosion of some of the primary atoms of the dielectric ; and we have further the important corroboration afforded by the fact that the colour of the light produced is found in a multitude of instances to depend on the kind of molecular matter present at the place of its production. Thus the colour of the electric spark in air is bluish ; in nitrogen it has a bluish purple tinge ; in oxygen it is white and less brilliant than in air ; in hydrogen crimson-coloured ; in carbonic acid greenish. When the discharge is through highly rarefied gases very beautiful luminous effects are presented. In an exhausted tube containing rarefied air we have, when the discharge passes, a luminous sheaf of purple colour ex- tending from the positive ball terminal to within a short distance of the negative ball, which latter is surrounded by 262 NEW THEORY OF LIGHT. a bluish glow.* If other attenuated gases are used other colours are obtained. If before exhausting, a little alcohol, or other volatile liquid is introduced, we obtain a series of transverse bright bands separated by dark spaces, and indeed if the exhaustion be carried sufficiently far, as in what is known as a Geissler tube, which contains some gas in a very attenuated state and has electrodes of platinum wire, the bright bands are produced without the presence of the volatile liquid (see fig. 6, p. 110). Some reference has been made already to the causes of the molecular condition which these appearances indicate (p. Ill), and some further reference will be made to these causes hereafter ; what we note here is that the phenomena referred to support our contention that the light produced by the electric discharge is due to concerted atom explosion, the precise nature of which depends partly on the kind of atoms present, partly on the conditions in which these atoms are placed, and that these phenomena indicate that the unmolecular ethers are by themselves absolutely non-luminous. As further evidence that this is so we may mention the fact that when an extreme exhaustion of a glass vacuum tube has been reached certain parts of the interior of the tube become luminous during the passage of an electrical discharge, the light emitted being green when German glass, blue when English glass is used. The portion of the glass rendered luminous depends on the form and position of the negative terminal, but, to show how completely the phe- nomenon depends on the molecular condition of the glass, we have the fact that use deadens the phosphorescence. f An observation made by Mr. Crookes on the effects in a * Effects in nature analogous to these luminous vacuum effects are seen in the case of auroras. t The extent of the falling off in luminosity is scarcely percep- tible at very high exhaustions, and there is a partial recovery when the glass is allowed to remain quiescent for a while. PHOSPHORESCENCE. 263 body of repeated excitation to phosphorescence by the electrical discharge may be given in this connection. He says, "After long experimenting with chemically pure alumina precipitated from the sulphate, a curious pheno- menon takes place. When sealed up in the vacuum two years ago it was snow-white ; but after being frequently submitted to the discharge for the purpose of exhibiting its brilliant phosphorescence, it gradually assumes a pink tinge, and on examination in sunlight a trace of the alu- mina line can be detected. The repeated excitation is slowly causing the amorphous powder to assume a crystal- line form.* Mr. Crookes has also noticed the coincidence of spectra of the phosphorescence produced by the solar rays in the phosphoroscope with the corresponding spectra of the phosphorescence obtained in high vacua. Substances which are readily excited to phosphorescence by being illuminated shine with great splendour when subjected to the negative discharge in a high vacuum. If, as we have argued, the luminosity in vacuum tubes is due to atom explosion induced by the presence of the un- molecular ethers of the discharge, the following account of the effect of electrical shadows t on this luminosity, quoted from a paper by the late Mr. Spottiswoode,J appears to throw some light on the nature of the distribution of the unmolecular ethers in a vacuum tube. " The two terminals of a Holtz machine were connected in the usual way with the two terminals of the tube, so as to produce a stratified discharge. A narrow strip of tinfoil, or a wire was- stretched along the tube opposite the column Paper read before Royal Society, May 19, 1881, by William Crookes, F.R.S. t See p. 100. " On Stratified Discharges. VI. Shadows of Striae," by William Spottiswoode, P.R.S., see Nature, No. 611, p. 254. 264 NEW THEORY OF LIGHT. of striae. The positive terminal of a second Holtz machine (in practice we used for this purpose a Tb'ppler machine) was connected with the tinfoil, and the negative terminal with one (either) terminal of the tube. An air spark, or interval across which sparks could pass was interposed in the part of the circuit between the machine and the tinfoil. The effect of this arrangement was this : In the interval between two sparks the tinfoil and tube became charged like a Leyden jar ; the tinfoil being the outer coating charged positively, and the gas inside serving as the inner coating, charged negatively. When the spark passed across the interval mentioned above, the jar (i.e., the tube) became discharged, and the electricity previously held bound on the two coatings was set free. When the first (say the internal) machine was not working or when it was dis- connected, i.e., when no regular discharge was passing through the tube, then, whenever a spark passed at the second (or ' external ') machine, a negative discharge with its accompanying Crookes' radiation took place from the inside of the tube next the tinfoil, and the opposite side of the tube became covered with a sheet of green phosphores- cence (the tube being of German glass). When however, other things remaining as before, a discharge from the internal machine was sent through the tube, and a good stratified column was produced, it was found that the green phosphorescence was entirely cut off from the parts of the tube opposite to the striae, while on the parts oppo- site to the dark spaces it remained, in the form of phos- phorescent rings, as brilliant as before It may be added that where, as is sometimes the case, through greater exhaustion, the striae became feebler in illumination and less compact in appearance the shadows cast by them lost proportionately in sharpness of definition and in com- pleteness of extinction of the phosphorescent light." As evidence that the gentler kinds of phosphorescence, PHOSPHORESCENCE. 265 including fluorescence (which is phosphorescence due to the incidence of light from some external source that ceases immediately after this latter is withdrawn), are due to the cause suggested, we may notice the significant fact observed by Sir John Herschel, that a beam of light is, by transmission through a solution of sulphate of quinine, though not sensibly weakened in luminous power, yet quite robbed of its power of producing fluorescence, all the fluoresence observed in the solution proceeding from a thin stratum adjacent to the surface acted upon by the stimu- lating rays. For the natural conclusion appears to be that, in harmony with one of our previous conclusions (p. 201), atoms are more readily exploded by ether waves of the wave-length of those they themselves produce ; that the ether waves of the fluorescent light, and of any ultra- violet rays also being emitted, have therefore the same wave-lengths as have such of the ether waves of the incident light as are concerned in producing the atom explosions to which they are due, and that the amalgama- tion of the former waves with the latter, in the way explained" above, accounts for the absorption by the solution of such of the incident waves as are capable of producing the fluorescence. As evidence of the occurrence of molecule destruction in phosphorescent bodies, we may cite the photo-electric phenomena which they exhibit when exposed to light,* for these, according to our theories, are due to ether liberation (see p. 183). Crystals long exposed to light are weakened in their photo-electric sensibility. Perhaps the occurrence of phosphorescence in organic bodies, sometimes observed, may also be regarded as evi- dence in the same direction ; for in the case of living organisms, we have a probable origin of atom explosion in the rapid molecular changes concerned in producing * Observed by Herr Haeckel. Nature, No. 580, p. 133. 266 NEW THEORY OF LIGHT. very rapid growth, or metamorphosis, or very swift move- ment, or frequently recurring waste and recuperation ;* and where phosphorescence is associated with decay, as in the familiar examples of Will o' the Wisp, and dead fish, atom explosion is, according to our theories, a necessary accompaniment of the molecular changes involved. Further, we may surmise, in this connection, that the astringent property possessed by many vegetable sub- stances whose solutions exhibit considerable fluorescence, in other words, the power possessed by such bodies of checking molecular change in the delicately adjusted matter of organic bodies, is due to a continual liberation of un- molecular ethers within them sufficient to effect an alteration of the ether conditions prevailing about the atoms of bodies to which they are applied. The fact that the light of phosphorescence belongs to the violet end of the spectrum, probably indicates that phos- phorescing substances are liberating an excess of positive ether (see p. 312). The close connection between phosphorescence and the incandescence of combustion seems to be indicated by the behaviour of phosphorus. This substance is, in its normal condition, on the border land between phosphorescence and combustion, the slightest inciting force commonly sufficing to carry it over the border ; its normal condition may indeed be regarded as a tame kind of combustion, chemical change accompanying the phosphorescence. Phosphorescence, like combustion, is in some cases pro- duced by friction. A familiar instance of this, known to * These suggestions will be better understood after the appli- cation of the theories of this treatise to a few of the phenomena of biology has been considered. Phosphorescence of the retina of the eye, seen particularly in some of the lower animals, will be argued to be an instance of association of the phenomenon with frequently recurring waste and recuperation. PHOSPHORESCENCE. 267 every schoolboy, is the production of a glow of light by rubbing two flints together. Unlike the case of colour due to absorption, in which the coloured light coming from a body is the residuum of the illuminating rays after the withdrawal of the rays "ab- sorbed," and where, therefore, this colour depends on the colour of the illuminating rays (see p. 258), the colour of phosphorescence is, in most cases, sensibly constant in the same substance, whatever the colour of the stimulating rays,* and we conclude from this that the phenomenon is due to certain atoms in a body being so conditioned as to pulsate very readily in response to the fluctuations of ether waves which encounter them, the explosion of one kind of these atoms involving the explosion of the others. Prof. Gr.G. Stokes has called attention to a fact analogous to the fading of colour alluded to above, which to some extent favours this conclusion. He finds that diminished excitability to phosphorescence follows continuous illumi- nation. Perhaps, however, this is more likely to be due to changed ether conditions produced by the molecule destruc- tion incident to phosphorescence than to any exhaustion of the supply of the particular atoms producing phosphores- cence exposed to the incident light ; it may be partly trace- able to both causes. A familiar fact favouring the suggestions made above, * This is only an approximate truth. Capt. Abney has shown that a phosphorescing body is differently acted on by waves of different wave-length ; e.g., when the spectrum is allowed to fall on an excited surface of Balmain's paint the blue rays enhance the violet phosphorescent light while the red rays extinguish it. Capt. Abney has further shown that there is a series of " octaves" in the blue end of the spectrum which refuse to quench violet light. Nature, No. 641, p. 355. And Prof. G. G. Stokes has observed the similar fact that sun- shine and artificial light excite different phosphorescence in the same substance. Nature, No. 658, p. 142. 268 NE\V THEORY OF LIGHT. that phosphorescence is due to the peculiar conditions of certain kinds of atoms in the phosphorescing mass, is that ether waves of very various wave-lengths are found competent to stimulate similar phosphorescence in solid and liquid substances. Thus some substances, as sulphate of quinine, are even stimulated to phosphorescence by dark rays beyond the violet end of the spectrum, indeed, generally, those bodies which exhibit phenomena of fluorescence have a faint nebulous light when held in the ultra-violet rays, as well as when held in the rays of the visible spectrum.* In conclusion, some facts respecting fluorspar may be quoted to show how completely the colour of the phos- phorescent light of a body, as well as its own proper colour, depend on the ether conditions surrounding its atoms ; that different ether conditions produce differences in the proportions exploded of the different kinds of primary atoms. Thus fluorspar which has its colour readily deepened by the application of heat, so that it is very customary before its use for ornamental purposes to exchange its natural blue for an amethystine tint by this means, loses both its colour and its phosphorescence if sufficiently heated.f The stability of the different tint acquired by fluorspar when gently heated must be regarded as an indication of the permanence of the changed ether conditions when once brought about by the application of heat. The normal colour of fluorspar is partially restored by * A similar power is possessed by the ultra-red rays. Thus if the beam from the electric lamp be concentrated by a suitable reflector, and all the luminous rays be then cut off by a glass cell containing a solution of iodine, the remaining ultra-red rays are still adequate to produce incandescence of a sheet of platinum. t It will be argued in the sequel that an increase of temperature is ordinarily caused by an increase in the quantity of negative unmolecular ether present (see p. 3] 5). TRANSPARENCY. 269 an electric discharge, which we have concluded is a flow of the unmixed ethers. Transparency. From the preceding arguments we see that opaqueness of homogeneous matter to light must be attributed to one of two causes. (a) Rigidity of the particles, such as we have con- cluded produces great reflecting power in the case of the metals. (&) Modification of the incident ether waves caused by interference between them and ether waves due to atom explosions which they set up within the mass. The fact that crystals, some of which are the hardest of all bodies, are often so highly transparent is in harmony with the supposition that they are examples of the cellular solid state and consist of aggregations of infinitesimal cells (p. 28) ; for it is readily seen that, a to and fro movement of the septa or cell walls being possible, ether waves which are sufficiently minute and, at the same time, sufficiently violent, will be able to pass from the partly expanded ether of one cell to the partly expanded ether of another without rupture of the cell walls. We may suggest that transparency of liquids is partly due to the presence within them of the unmolecular ethers, to whose increased liberation the liquid state has been attributed, and it is possibly owing to this that water is more transparent than ice, and oil more transparent when fluid than when congealed. We may notice here, as a link between transparency and non-conduction of electricity, that we connect both phenomena with a high mobility of the ether particles of the body in which they are observed, and, in harmony with this, that bodies which are transparent to light 270 NEW THEORY OF LIGHT. are insulators, or non-conductors of electricity, and that conductors of electricity are always opaque to light. The remarkable researches of Prof. Graham Bell have recently shown that even ebonite, an insulator which is most opaque to the rays of the visible spectrum, is transparent in no small degree to some ether waves outside it. 271 CHAPTER XXIY. DOUBLE EEFRACTION AND POLARIZATION. TTTHEN a crystal of Iceland spar is laid upon a page of ' ' a book it transmits a double image of each letter seen through it, and if the crystal is turned round while still in contact with the paper, one image revolves around the other which remains unmoved, and the image which revolves appears further from the eye than the other image. The property of double refraction of which this is a striking instance is possessed in a lesser degree by many other crystals which, like Iceland spar, do not belong to the cubic system. To exhibit the phenomenon known as polarization, two thin slices of tourmaline cut parallel to the crystal axis are generally used. This crystal does not exhibit double refraction so strikingly as Iceland spar does, because it has the property of very speedily quenching the less refracted ray, so that unless a very thin slice indeed is used, but one ray emerges whose index of refraction is variable. When the two slices are laid flat upon each other, and so that the axis of the one crosses the axis of the other at right angles, no light passes where they cross, but as one of the slices is turned round upon the other and the angle between the axes diminished, light begins to pass, until, when the axes of the two crystals become coincident in direction, the combination of the two slices is as transparent as a single slice of the double thickness 272 NEW THEORY OF LIGHT. would be. Three positions of the tourmaline are depicted in the accompanying figure. The immediate deduction from the foregoing facts is that transmission though some crystals gives to waves of light a distinctive polarity of a certain kind having reference to the direction of the crystal axis, and that the two rays into which a single ray is found divided after transmission have this polarity in directions at right angles to one another, and further that the particles within the crystal whose motions convey light move faster in rays whose polarity has one direction, than in those whose polarity has the other direction. The theory of double refraction and polarization by trans- mission o/ered in this treatise is : (a) That in those crystals N9 1 N?2 N? 3 which exhibit these phenomena the cell walls, or septa, whose presence we have concluded to be characteristic of the cellular solid state (p. 28), are symmetrically situated with respect to the crystal axis, and that their arrangement is such that ether motions com- municated from cell-interior to cell-interior through the flexible cell walls experience different degrees of resistance and retardation according to the inclination of their path to the crystal axis ; in some crystals the retardation being greatest in the direction of the crystal axis, in others least, (b) That when ordinary ether waves pass into such a crystal the effect of the different degrees of retardation experienced by moving ether particles, according to the direction they are taking, is that each series of fluctuations of alternate radiation from and return to a prism-axis, found in ordinary ether waves (p. 203) furnishes two series of modified fluctuations having different velocities of propaga- tion^ one series springing from the portions of the original DOUBLE REFRACTION AND POLARIZATION. 273 series found in opposite quadrants about the prism-axes whose bisectors are at right angles to the crystal axis, the other series from the portions found in the remaining quadrants. Thus, if fig. 27 represents a transverse section of a few of the prism-shaped surfaces of maximum ether condensation in a group of ordinary ether waves made at the surface of the crystal held with its axis horizontal, it is supposed that one series of modified fluctuations will spring from portions of the original fluctuations occurring within angles such as m A n } p a q, the other series from those occurring within angles such as mAp,nAq. (c) Finally, that the paths of the moving ether particles in one series come to be mainly, though not exclusively, in planes at * right angles to the crystal axis, while those of the moving ether par- ticles of the other series similarly approximate to the plane direction perpendicular to this containing the crystal axis. We shall now bring forward argu- J ' Fig. 27. ments in support of this theory. And first as to the section of it we have marked (a) there is abundant evidence in the different conductivity of uniaxal crystals in different directions for heat, and also for electricity, as well as in their optical properties, to prove the existence of symmetry of arrangement of their particles with respect to the crystal axis (see p. 183), and the supposition that the arrangement is such as to involve more retardation of ether motions occurring in some directions than of those occurring in others is evidently quite in harmony with the conclusion that crystals have a cellular structure of the kind supposed. Next as to the sections of the above theory which we have marked (b) and (c). We will take the simple case of 18 274 NEW THEORY OF LIGHT. ordinary light falling vertically on a plate of double refracting crystal, cut parallel to the axis, the ether retardation being least in the direction of this axis,* and endeavour to show that each group of ordinary ether waves, such as we have described, will, in traversing such a crystal, be separated into two modified groups, one of which will come to have its vibrations almost solely in planes at right angles to the crystal axis, the other almost solely in planes in the direction of this axis, drawn perpen- dicular to the crystal surface. The following is the line of argument we take for this purpose : We have said that where ether waves are tra- versing an isotropic medium each of the surfaces of maximum ether condensation is equidistant from its two generating centres, or axes, and therefore bisects at right angles transverse lines drawn from one axis to the other (see fig. 27). But in the case of waves traversing a medium of non-isotropic crystal the different velocities of the ether vibrations in different directions will cause these surfaces, though still each equidistant from its generating axes as measured by time, to be no longer equidistant as measured by actual length. Our first step is to trace the positions of surfaces of maximum ether condensation as presented immediately within the crystal. Now we suppose that the relative velocities of ether particles similarly projected in different directions within the crystal are represented by radii drawn in these direc- tions to a spheroid whose principal axis has the direction of the crystal axis and whose principal and subordinate axes are in the ratio of the velocities of particles similarly projected in the direction of the crystal axis and in planes at right angles to this axis respectively.! And upon this Such are called negative crystals. f In the case of a positive crystal the spheroid referred to will be an oblate spheroid, in the case of a negative crystal it will be a prolate spheroid. DOUBLE REFRACTION AND POLARIZATION. 275 supposition it is evident that, ; since in the case supposed the relative position of the prism-axes continues absolutely unchanged by their entry into the crystal because there is no refraction, the locus traced by each surface of maximum ether condensation in a plane just within the crystal, and parallel to its surface, is the locus of the points of intersection of pairs of equal and similar ellipses, whose centres have the relative situation of the points of intersection of the two generating prism-axes with the plane of the crystal surface, and whose major axes are all horizontal, and bear to their respective minor axes the Fig. 28. ratio of the two limiting velocities within the crystal which are above referred to. To ascertain these required loci we have to solve the following problem : Problem To find the locus of the points of intersection of pairs of identical ellipses, which have their centres at two given points, all the ellipses having their respective axes parallel, and the lengths of the major and minor axes of each pair having a constant ratio : Let A, B (fig. 28) be the two given points. Bisect A B in c, which from considerations of symmetry will evidently 276 NEW THEORY OF LIGHT. be one point upon the locus. Then if any pair of identical ellipses drawn as prescribed, intersect each other in two points F, G, the points F, c, G will lie in a right line, which is the locus required. For let c x a horizontal line, and c y a vertical line, have the directions of the major and minor axes respec- tively. Draw A D, B E perpendicular to y c ?/', these lines being evidently equal to each other. And then let a plane be conceived, drawn through y G y' to make an angle with the plane of the diagram, whose cosine is the given ratio of the minor and major axes, and on this plane project Fig. 29. the lines we have drawn on the original plane by a series of perpendiculars dropped from these lines on to the plane thus conceived. Then the nature of this projection is evidently such that the projections of all ellipses drawn as prescribed will be circles, and since it is evident from a very simple geometrical consideration, that the locus of the points of intersection of pairs of these circles is a straight line drawn through the intersections of any pair, it follows that the locus of the intersection of the ellipses of which the circles are projections, is also a straight line drawn DOUBLE REFRACTION AND POLARIZATION. 277 through the points of intersection of any pair of ellipses. To exhibit diagrammatically, in accordance with this conclusion, the nature of the disposition of the prism- shaped surfaces in some group of ether waves passing into a crystal in the manner supposed : Let A, A, A, etc. (see fig. 27, p. 273), represent the inter- sections of some of the prism-axes of the group with the surface of the crystal laid with its axis horizontal. Project these intersections in the way above described, the plane of projection cutting the original plane in y y' (this is a simple proceeding, as every vertical length in the original is represented by an equal length in the projec- tion, and every horizontal length by a length which bears to it the given ratio of the two velocities). Let A' A' A', etc. (fig. 30), represent the resulting projections. Then, since the projections of all ellipses drawn as pre- scribed will be circles, the projections of the loci of the intersections of pairs of these ellipses (which loci we have seen are those traced by the surfaces of maximum condensation in a plane just within the crystal parallel to its surface) will be straight lines drawn to bisect at right angles lines joining the projections (A') of the wave centres. When these bisectors have been drawn to meet one another (see fig. 30), we can, by a simple method of proportions, taking every vertical length the same, and every horizontal length in the inverse of the given ratio of the limiting velocities, construct the loci themselves (see fig. 31). Finally, to show that each group of ordinary ether waves will, in addition to experiencing this change, be presently separated into two modified groups in the way stated : While it is evident that the first set of similar fluctua- 278 NEW THEORY OF LIGHT. tions, radiating abreast of one another from the various prism-axes of one of the wave groups after its entry into the crystal, will have the same rank of advance at all the prism angles ; these angles being all similarly situated with respect to the three prism-axes nearest to them ; we see that the advance of these fluctuations will be less rapid along the prism surfaces in which the most retarded radiations meet, than along those in which the least re- tarded radiations meet ; and that, as succeeding pulsations follow one another, an increasing difference of rank of advance of different portions of the fluctuations will be exhibited. It is difficult to trace the precise modification of a group of waves which must result, but it is evident that since the radia- tions occurring in two opposite quadrants about each prism centre (as m A p and n A q, fig. 27, p. 273) are met by neighbouring radiations before those occurring in the re- maining two quadrants (as mA.n and p A q) are thus met, the por- tions of an ether wave in one pair of quadrants, will, after the first pulsation, be unsupported by the portions in the other pair, and will therefore, instead of concentrating at a prism-axis, have a parallel motion of their particles, each particle moving approximately in a plane parallel to the plane of incidence drawn bisecting the quadrant ; and we readily perceive the result will be the division of each wave group into two modified groups similar to one another, one of which has the bulk of its ether particles moving in planes at right angles to the crystal axis, the other in planes containing the crystal axis, and the concentra- tions in each taking place along parallel planes, probably of small extent, instead of as in the ordinary ether waves. POLARIZATION BY REFLECTION. 279 Similar reasoning would .apply to other more complex cases. The plane drawn in the direction of propagation of a polarized ray at right angles to what according to this conclusion is the main direction of vibration of the ether particles is commonly called the plane of polariza- tion of the ray, thus, in the case above supposed, of light polarized by a uniaxal crystal, the plane of polarization of the ordinary ray, i.e., of the ray whose vibrations are at right angles to the crystal axis, is the plane in the direction of propagation which contains this axis. That the two modified wave groups produced by polarization have different indices of refraction is evidently accounted for by the different velocity of ether particles moving in the two different directions of vibration. The experiment with the two tourmalines above de- scribed shows that when the plane of polarization of a polarized ray which falls vertically upon a slice of uniaxal crystal cut parallel to the axis is not either at right angles to the axis of the crystal or containing this axis, two rays are produced, as in the case of the transmission of an ordinary ray through a double-refracting crystal, the only difference being that the two rays now have different intensity if the plane of polarization of the original ray is nearer to one direction of polarization in the crystal than to the other. We naturally attribute this separation of a polarized ray into two rays to some such separation of each ether fluctuation into two through the retardation of one portion of it compared with another as that we have just pictured in the case of polarization of ordinary light. Polarization by Reflection. It was discovered by Malus in 1808 that light reflected at an oblique angle from a glass surface is polarized, and 280 NEW THEORY OF LIGHT. it has since been found that the transmitted light is also feebly polarized, the plane of polarization of the latter being at right angles to that of the former. It has also been found that other transparent reflecting surfaces besides glass exhibit the same effects. When light is reflected from a plate of glass, or of some other transparent isotropic medium at a particular angle of incidence known as the polarizing angle,* which is such that the direction of the reflected light is per- pendicular to the direction of that refracted, all the reflected light and a proportion equal to it of the trans- mitted light are found to be polarized, the plane of polarization f of the reflected ray being in all cases the plane of incidence and reflection. And, finally, when a polarized ray is incident upon a plate of glass at the polarizing angle, and the plane of polarization of the ray is at right angles to the plane of incidence, no sensible reflection takes place, and the whole ray is transmitted. To make the phenomenon of polarization by reflection and refraction more apparent it is usual to employ a pile of about a dozen glass plates, so as at once to increase the amount of light reflected and strengthen the polariza- tion of the light transmitted. We will now endeavour to show that the same theory of polarization as that above suggested in the case of polarization by crystals is applicable to the case of polarization by reflection. We concluded in a previous chapter that when light falls obliquely on a surface between two different trans- parent media the proportions of any given fluctuation transmitted and reflected respectively will not be the same in all parts of it, but will vary according to the * This angle for glass is generally about 56 35'. t See p. 279. POLARIZATION BY REFLECTION. 281 direction of radiation of the T> form A B, or A C, i.e., so that each molecule contains - 2 two and a half atoms. It is evident we can as readily conceive further combina- tion to occur with molecules of this kind as with molecules whose symbols contain whole atoms only. Next as to the analysis, or breaking up of complex atom combinations through the operation of the law of symme- rical intermixture. If a body composed of molecules containing more than two atoms passes beyond the gaseous state in which two atoms in a molecule are expanded to a state in which three or more atoms are expanded, we should evidently look for a loss of equilibrium under the changes of pressure to which the law of symmetrical intermixture is due, and for a breaking up of the mass into smaller masses, each con- sisting either of one kind of expanded atoms only or of two different kinds of expanded atoms in equal numbers. And in harmony with this it is suggested that the origin of the law already referred to, that, whatever the volumes of different gases combining, it is always reduced to two on combination or, as we should express it, that a compound cannot have more than two kinds of atoms greatly ex- 356 JTEW'-TtTEORY OF CHEMISTRY. , * ' - . panded is that, when in any given mass equal numbers of two kinds of atoms are already expanded, the expansion of more atoms is always productive of the breaking up of the compound into simpler forms. Thus in the case of the higher chloride of phosphorus, p PCI ,* (or C1 5 ) being readily resolved into the lower * 2 / chloride, PC1 6 , and chlorine by the application of heat, it is suggested that the change is due to the rise of temperature producing a gaseous state of the higher chloride in which six atoms are expanded, i.e., a state which, according to the scheme of notation above proposed (p. 344), would be written PC1 5 C1 5 , and that the law of symmetrical inter- mixture acting on this unsymmetrical gas breaks it up into a symmetrical gas of the lower chloride, and chlorine. As an example of the very common form of analysis known as dehydration, to which the explanation just given applies, we have the conversion of ammonium formiate, H 6 2 CN, into hydrocyanic acid and water by the action of heat. Probably the process is expressed by the equation As another example of analysis to which also a similar explanation applies. Potassium chlorate, KC10 3 , if heated decomposes, first yielding a mixture of potassic perchlorate KC10 4 , potassic chloride, KC1, and oxygen, but ultimately being entirely resolved into potassic chloride and oxygen. Here it is suggested that, on the rise of temperature of the mass causing some portions of it to vaporize, different states of vapour expansion are, owing to slight differences of condition at different points, simultaneously produced, and that thus we have side by side, a state of semi-expan- * Phosphorus is taken to have double the atomic weight usually stated (see p. 345). SYMMETRICAL INTERMIXTURE sion in which one atom only is, expanded^lirisrcfi^niolecule KC10 3 , and a state of dissociation in which, all the atoms being expanded, the mass breaks up into potassic chloride, KC1, and oxygen ; that the law of symmetrical inter- mixture causes the molecules of chlorate which have but one atom only expanded to intermix with atoms of oxygen liberated from the dissociated molecules, and that thus we get at first the perchlorate KC10 4 , but that a higher tem- perature dissociates the molecules of perchlorate by ex- panding all their atoms so that the whole mass is resolved into potassic chloride* and oxygen. As an example of analysis in which the sudden expansion of the atoms of a compound to the gaseous state is evidently associated with the dissociation of the atoms we have the fact that iodide of nitrogen (a black powder obtained by digesting iodine for half an hour in a cold solution of am- monia), explodes upon the slightest touch, indeed often without assignable cause. The explosion is remarkably sharp and sudden ; fumes of iodine are produced and a faint light is emitted.! The kind of chemical analysis known as electrolysis will receive a different explanation from that just given of ordinary cases of analysis (see p. 389). According to the views here propounded, any atom in a mass, whether the mass is solid, liquid, or gaseous, is equally related to all the atoms similar to one another which touch it, and when we talk of a molecule we do not mean a group of particular individual atoms, but merely an undivided unit of mass which contains the proper proportions of the different kinds of matter composing the different atoms ; our views are therefore not precisely in accord with the conception generally understood by the law of Avogadro, * For the reason of the atoms of potassium and chlorine pairing together, see p. 358. t The subject of explosions is considered subsequently. 358 NEW THEORY OF CHEMISTRY. " that equal volumes of all substances when in the state of gas and under like conditions contain the same number of molecules." If, however, in deference to the law just referred to, the practice is followed of so writing the symbols of molecules that each shall contain two expanded atoms when the mass is gaseous, it is evident that as the result of the equality prevailing between minimum masses of different gases to which allusion has already been made, and neglecting the occupation of some small amount of space by the atoms remaining condensed, we have the following law covering much the same ground as that covered by the law of Avogadro. Equal volumes of all substances when in the state of gas and under like conditions contain approximately the same number of expanded secondary atoms. Finally let us endeavour to explain the interchange of atoms occurring in metatheses. We may either suppose that the compounds which effect an interchange of atoms have at first each only one atom in a molecule expanded, and that the first step is the pro- duction by symmetrical intermixture of complex molecules composed of all the atoms of both original compounds, and that directly upon this combination occurring more atoms expand, whereupon, according to the law just referred to above, the compound, which has thus become unsymmetri- cal, breaks up, different atoms from those formerly united now pairing together. Or we may suppose, which seems very likely, that the first step is that local intermixture of all the atoms which must, it is evident, take place wherever the boundaries of gaseous masses of the original compounds come in contact, even though these compounds are in the gaseous state produced by expansion of two kinds of atoms. As to the origin of differences of chemical affinity that determine in each case which atoms shall group together SYMMETRICAL INTERMIXTURE OF GASEOUS ATOMS. 359 when, as just supposed, the. law of symmetrical inter- mixture breaks up an unsymmetrical mass (i.e., a mass in which more than two kinds of atoms in equal numbers are expanded) into patches of symmetrical composition i.e., into masses which have two kinds of atoms in equal numbers expanded, we suppose : That, since any given change of pressure will evidently produce more vigorous movements in a small mass to which it is applied the greater the difference in their readiness of compression of the different kinds of atoms in contact (see p. 9), we shall in all cases have those of the expanded atoms which differ most in readiness of compression pairing together and, generally, the nature of the distribution of the expanded atoms of different kinds will be regulated by their relative readiness of compression, certain definite groups of these atoms being therefore formed in each particular case. Further, that, as to the distribution of those of the atoms concerned in any metathesis which continue highly condensed during the process, these atoms will follow the destination of those of the expanded atoms between which and them the greatest and most unbroken cohesion subsists. It would appear, however, that there are some few excep- tional cases in which the condensed atoms are thrown down from the changing mass in an uncombined state. As probable instances we may refer to the cases in which the metal silver is thrown down from its compounds. In these cases we suppose that the atoms of silver are those which remain condensed when the compound becomes gaseous, and that the silver forming these atoms is aggregated together and, as it were, shaken out of the mass in the condensed state*: For example, when hydrofluoric acid is obtained by heat- ing silver fluoride in an atmosphere of hydrogen, we sup- pose that the metathesis is not due to expanded fluorine atoms mixing more readily with expanded hydrogen atoms * See as to this conception our theory of electrolysis, p. 391. 360 NEW THEORY OF CHEMISTRY. than with expanded silver atoms, but to the production of an unstable compound, FAgH, of which at the moment of production the fluorine and the hydrogen atoms are ex- panded, and that the condensed silver is as it were shaken out of this compound while the gaseous state continues that, to express it in our notation, FAg + H = FHAg = FH + A g . It may perhaps be supposed to favour the theory above submitted of the cause of the particular grouping of the atoms produced in most cases of metathesis, that we commonly find those elements pairing together whose places in the electro-chemical series (see p. 393) are furthest apart, i.e., those which presumably differ most in ether composition and readiness of compression. Some simple cases of metathesis, to which we shall presently refer, will be found to exemplify this. In some cases of metathesis we have evidence that, as above suggested, the first step in the process is the forma- tion of complex molecules containing all the atoms of both compounds concerned in the reaction. Thus hydrogen chloride, HC1, combines directly with sulphuric anhydride, S0 3 , to form sulphuric chlorhydrate, and it is only when the latter is heated in a closed vessel to 170 C. that we get it decomposed into sulphuric chloride Cl a S0 2 , and sulphuric acid, H 2 S0 4 . The atoms expanded when the law of symmetrical inter- mixture accomplishes the synthesis first referred to are probably those indicated thus HCl + OS0 2 = HOC1S0 2 = HC1S0 3 , and those expanded when the subsequent analysis which completes the metathesis occurs, thus O = CK)f+HOfo. - A SYMMETRICAL INTERMIXTURE OF GASEOUS ATOMS. 361 The fact of the division of the, sulphur atoms between the two compounds thus ultimately produced may possibly be due to their being, as we shall presently conclude the atoms of oxygen in ozone are (p. 367), in two different electrical states, one-half in a more positive and the other half in a more negative state, and to the more positive atoms going to one compound, the more negative atoms to the other. It would appear, according to the above theories, that in many cases of analysis the atoms which remain condensed during the process are divided, some following the destina- tion of one kind of expanded atoms, some the destination of another kind ; although generally the same kind of atoms do not appear to be divided, as we have supposed they are in the case just referred to. As a probable example of the division of the atoms which remain condensed, ammonic nitrate when gently heated is resolved into a mixture of the vapours of nitrous oxide and water. According to the theories above submitted we suppose this change to be due to more than two atoms in a molecule becoming expanded, and the unsymmetrical gas thus pro- duced breaking up into symmetrical gases, the atoms which remained condensed, some following the destination of one kind of expanded atoms, some that of another. Probably the process would be expressed by this equation NH 2 O 3 NH 2 = NON + 2HOH. It affords some experimental support of the above theories, that in several cases where compounds are known to us such as would be intermediate steps in the formation of complex compounds in the manner supposed, we find some interesting facts showing the existence of connecting links between different compounds belonging to the same series. Thus in reference to the several known compounds of nitrogen and oxygen : 362 NEW THEORY OF CHEMISTRY. The simplest of these compounds is nitric oxide, NO, a gas having normally the same volume as its uncombined constituents, and the formation of which, according to the above, we suppose to have been preceded by a symmetrical intermixture of the gases oxygen and nitrogen in equal quantities.* When this gas is mixed with oxygen it immediately com- bines with it in the volume proportions 2 : 1 and we get a second compound, nitric peroxide, N0 2 . This atom combination is explained in harmony with the above theory if we suppose that in the presence of oxygen one atom in each molecule NO becomes condensed, and that thereupon the symmetrical intermixture follows be- tween equal volumes which is expressed by the equation NO + O = NOO. Further the compound N0 2 is known to us in two gaseous states, both in harmony with our theories ; for at low tem- peratures its volume agrees with the conception that but one atom out of the three composing each molecule is expanded, but when heated its volume increases faster than would normally be the case till at 150 its volume agrees with the conception that two atoms out of three are expanded. Nitrous oxide, N 2 0, we should suppose to be derived from a symmetrical intermixture between nitric oxide and nitro- * A reason has already been suggested (see note *, p. 348) why in some cases an intermixture of this kind is followed by chemical union, and in other cases is not so followed. The cause of chemical union is more fully treated, p. 370. t We suppose therefore that under one set of conditions gaseous nitric oxide has only its nitrogen atoms expanded, and under another set of conditions only its oxygen atoms expanded, under normal conditions both its nitrogen and its oxygen atoms expanded. SYMMETRICAL INTERMIXTURE OF GASEOUS ATOMS. 363 Then we have nitrous anhydride, N 2 3 , apparently pro- duced together with nitric peroxide, N0 2 , when nitric oxide is mixed with oxygen, and this compound we may suppose is derived from a symmetrical intermixture between nitric oxide, NO, and nitric peroxide, N0 2 , when each of these has but one atom in a molecule expanded. And finally we have the unstable compound, nitric anhy- dride, N 2 5 , whose transparent prismatic crystals melt at about 30 C., and which gradually decomposes even at ordinary temperatures into oxygen and nitric peroxide ; and this compound we may suppose to be the result of symmetrical intermixture between nitric peroxide, N0 2 , and groups of atoms, N0 3 , when both these groupings have but one atom expanded in a molecule. Thus NOO + N0 = NON0 = N0 25 . Again, as to the two compounds of carbon and oxygen known to us, carbonic oxide, CO, and carbonic dioxide, C0 2 , both of which in their normal condition have a degree of gaseous expansion which leads us to suppose that two atoms are expanded in each molecule. Favouring our view that the atom combination presented by carbonic dioxide, C0 2 , is due to symmetrical intermix- ture between carbonic oxide, CO, when in the state marked (6) in which one atom is expanded (p. 348) and oxygen, we have the fact that carbonic oxide is formed when the supply of oxygen is small. As possibly connected with the supposed difference of structure of the two gases that carbonic oxide has no atoms condensed, while carbonic dioxide has one atom in a molecule condensed we may refer to the different be- haviour of the two gases. Thus carbonic oxide is combust- ible producing carbonic dioxide (CO + = C0 2 ) ; carbonic dioxide is not combustible, and will not support combustion. 364 NEW THEORY OF CHEMISTRY. Carbonic oxide is extremely poisonous being capable of displacing the oxygen in the blood ; carbonic dioxide is merely inert. When carbonic dioxide is passed over red-hot carbon, carbonic oxide is produced. Probably the vapour condi- tions prevalent at the moment when the change takes place are represented by the equation OCO + C = OCOC = 2CO. Next, as to the two oxides of barium, barium oxide, BaO, and barium dioxide, Ba0 2 , we have the significant facts that the higher oxide, Ba0 2 , when strongly heated, gives up one-half of its oxygen and produces the lower oxide, BaO ; and that the latter is reconverted into the dioxide when it is gently heated and moist air passed over it. Evidently our theory of the production of barium oxide and oxygen from strongly heated barium dioxide would be that the latter comes to have three atoms in a molecule highly expanded, and that the unsymmetrical gas thus produced is by the law of symmetrical intermixture broken up into the symmetrical gas, BaO, and oxygen. And the production of the atom arrangement presented by the dioxide from gently heated barium oxide, BaO, and oxygen we should suppose to be due to symmetrical inter- mixture between the latter when in a gaseous state with but one of its atoms expanded and oxygen ; thus BaO + O = BaOO. Next, as a typical case of a sulphate allying itself with different numbers of molecules of water under different conditions, we have the facts that magnesic sulphate, MgS0 4 '7H 2 (which according to the above arguments we suppose to be the result of seven successive symmetrical intermixtures with molecules of water), when it is heated SYMMETRICAL INTERMIXTURE OF GASEOUS ATOMS. 365 gives up five molecules of water with facility, the sixth less rapidly, the seventh not until a temperature of between 200 and 300 C. is reached. The first of these analyses is probably represented by the equation i (MgS0 4 7H 2 0) = OH 6 H = ' / the second by the equation i the third and final analysis is probably due to the ex- pansion of the manganese or sulphur atoms. Finally, among the compounds of carbon and hydrogen, the following complete series, such as we have supposed to be produced by successive acts of intermixture, is known to us (all the terms of this series are gaseous under normal conditions). The vapour density of Ethine or Acetylene, HC, Ethene or Ethylene, H 2 C, Ethane, H 3 C all these three compounds indicates that one atom only in a molecule is greatly expanded.* Methane (marsh gas), H 4 C ; the vapour density of this compound indicates that two atoms in a molecule are greatly expanded. The first term, ethine, is formed directly from its elements by causing the electric arc to pass between poles of dense carbon in an atmosphere of hydrogen. The second term, ethene, is produced by the combination of ethine with nascent hydrogen. * It is owing to this that the three compounds are ordinarily written H 2 C 2 , H 4 C 2 , H 6 C 2 respectively. 366 NEW THEORY OF CHEMISTRY. The third term, ethane, H 3 C, is produced by the action of hydrogen upon an ethene haloid ether, H 2 CI (ordinarily written H 4 C 2 I 2 ), a compound which, as we see, contains the preceding term H 2 C. Thus H 2 CI + 2H = H 3 C + HI (hydriodic acid).* The fourth and final term, methane, H 4 C, is similarly obtainable from the preceding term combined with iodine. Thus- H 3 CI + 2H = H 4 C + HI.* We may remark that as we pursue our arguments fur- ther the conclusion will appear not unreasonable that every individual of the multitude of carbon compounds of organic chemistry which is sometimes called the chemistry of the carbon compounds owes its atom composition to successive symmetrical intermixtures, under particular conditions, and in certain proportions, of the four terms just referred to, HC, H 2 C, H 3 C, H 4 C, with each other, and with other molecules or atoms. The following interesting example of two different syntheses of the same compounds produced by two different sets of outward conditions is quite in harmony with the theory which has been offered that the nature of a chemical reaction depends on the nature of the gaseous states of the bodies taking part in it at the moment when it occurs. When finely-divided oxide of manganese, Mn0 2 , and sulphur dioxide, S0 2 , are brought together in water ; if the liquid is kept cool we get manganous hyposulphate, MnS 2 6 ; but if the temperature is allowed to rise, we get the sulphate MnS0 4 . We may here offer a suggestion as to the production of ozone , a peculiar form of oxygen which has in the gaseous * An explanation of the two metatheses, H 2 CI 4- 2H = H 3 C + HI and H 3 CI + 2H = H 4 C + HI, is suggested in the sequel. SYMMETRICAL INTERMIXTURE OF GASEOUS ATOMS. 367 state just two-thirds the expansion of oxygen in its normal condition, and is strikingly different from the latter in its chemical behaviour. From its volume it is evident we should, according to the theory which has been offered above, suppose ozone to contain one condensed atom of oxygen to every two expanded atoms, so that its symbol should be written O 2 0, or O , according to whether we write it for each & molecule to contain two similar expanded atoms, or only one. But the difficulty presents itself how is the law of symmetrical intermixture, to whose agency we have just attributed the production of atom combinations of this nature, applicable to the formation of a body whose atoms are all of the same kind, since the action of this law depends on the atoms coming together having different readiness of compression. The explanation suggested is that where ozone is formed secondary atoms of the same kind, being subjected to different electrical conditions, are experiencing different degrees of internal atom explosion, and are consequently in different electrical states, i.e. f have different propor- tions of the unmolecular ethers present among the primary atoms composing them ; and that, owing to this, we have atoms of the same kind manifesting different elasticity, or readiness of compression. This view receives countenance from the fact that ozone is produced from normal oxygen solely by the action of electricity ; it is generally formed artificially by the influence of the silent discharge on pure, very dry oxygen whose temperature is being kept down by the presence of fragments of ice. We suppose, then, that through some atoms of oxygen having different readiness of compression from others, the law of symmetrical intermixture operates just as though 368 NEW THEORY OF CHEMISTRY. atoms of different kinds were present, and that the forma- tion of ozone is due to two acts of symmetrical intermix- ture. o + o = oo ; Oo + O = O 2 o. As we should expect, if ozone has one atom condensed, its conversion into oxygen may be effected by heat. Thus when ozonized oxygen is passed through a glass tube heated to 110 C. slight decomposition of the ozone takes place ; at 200 the decomposition is very rapid, about 97 per cent, being converted into oxygen ; and below 300 decomposition is complete. O 2 = OO + O or 3O. The great oxidizing power of ozone may perhaps be due to the condensed state of some of its atoms causing the electrical effects to be more powerful when it is brought in contact with bodies which are emitting a different pro- portion of the unmolecular ethers ; this suggestion will be understood better presently. The supposition that the different atoms preserve their identity in compounds, each having its characteristic in- fluence in determining the qualities of the compounds of which it forms part, seems supported by the fact that a gradation of physical properties is observed in what are known as homologous series of compounds. Thus, taking the series of paraffins in which each term differs from the preceding in having an additional group, CH 2 , in its molecule. Marsh gas, CH 4 Ethane, C 2 H 6 Hexdecane, C 1fi H 7 16 *. SYMMETRICAL INTERMIXTURE OF GASEOUS ATOMS. 369 we observe that the first four members of the series are gaseous at ordinary temperatures, and that the succeeding terms are liquids of increasing specific gravity as we pass along the series until in the final term we have a solid body ; and further that the boiling points of the series are in increasing order, the differences approximating to a regular law of gradation. In closing this chapter we may state that the facts of crystallization will in the sequel be shown to furnish the completest evidence that the several atoms of crystallizing compounds occupy distinct portions of space, and that they are not linked together in groups to form concrete molecules, but that every atom is equally related to all the atoms similar to one another which touch it. These facts, and the conclusions as to the formation of molecules which we shall thus deduce from them, will therefore be found entirely in harmony with the theories just propounded. 370 CHAPTER XXXIV. THEORY OF THE PRODUCING CAUSES OF CHEMICAL CHANGES APPLICATION OF THE THEORY TO SOME CASES OF SYNTHESIS AND METATHESIS QUANTIVALENCE. IN the last chapter we endeavoured to show that the law of symmetrical intermixture is adequate to produce the various kinds of atom combination found in different chemical compounds if we suppose that various appropriate changes of state of the molecular matter undergoing chemical change take place at different stages of this change. Thus we suggested that methane, H 4 C, may be the ultimate product of four successive acts of symmetrical intermix- ture, if HC, H 2 C, H 3 C, the supposed respective products of the first three acts, each, as it is formed, passes from the gaseous state of its formation in which two different atoms are expanded in each molecule, to the state of semi-expan- sion in which one atom only is expanded. We shall now endeavour to point out some probable causes of such changes of state as are thus supposed. It has been suggested (p. 301) that both mere change of bulk and change of state of molecular bodies produced by heat are due to a lowering of the minima of the fluctuating values of the cohesion of some of the atoms composing these bodies, and that this is due to an increase in the quantity of the unmolecular ethers present within the inter- stices of the mass affected, which causes these ethers and the atoms at the molecular surfaces in contact with them to experience a fall of density. CAUSES OF CHEMICAL CHANGES. 371 In harmony with this we now make the general proposi- tion that all changes of state of molecular matter are due to alteration in the proportions or quantity or density of the unmolecular ethers present at the point where a change is experienced. And as to those cases where, on two different molecular masses being brought together, chemical change occurs spontaneously, without the aid of heat, or light, or chemical rajs, or any other external agency, such as, according to the arguments of this treatise, would supply unmolecular ethers or produce ether liberation ; it is suggested that when the contact between the two different kinds of matter takes place, changes in the ether conditions, productive of the requisite changes of state, are in most cases brought about by electrical action, the result of the different masses brought together emitting different proportions and quanti- ties of the unmolecular ethers.* We suppose, in fact, that the excess of positive ether emanating from one kind of matter meets the excess of negative ether emanating from the other kind, and produces an accumulation of mixed unmolecular ethers, and a consequent rise of temperature (see p. 319). There is, however, another way in which the contact of one kind of matter with another would appear to cause change of state, and which may account for some cases of spontaneous chemical change. The ether conditions prevalent about one kind of matter will, we argue, some- times extend to particles of another kind of matter which are in close proximity, and modify the normal ether con- ditions of the latter. What we suppose to be examples of this effect of the presence of one kind of matter on another will be referred to immediately. * We have based the explanations of several electrical phenomena, on the conclusion that different substances emit different proportions of the two ethers (see pp. 74, 111, 130, and 141). 372 NEW THEORY OF CHEMISTRY. Like the cases of chemical change where a spark from without is the inciting cause, and the area of chemical action at once extends on every side from the mere point at which it originated, we conceive that chemical change occurring spontaneously is at first very local and very feeble, and that it is intensified and extended by means of the ether liberation and consequent heat it produces. Supporting the theory to which we are led by the above, that changes of the ether conditions prevalent about molecular masses are instrumental in causing them to undergo chemical change, we have the well-known fact that the temporary application of heat, which, according to our previous conclusions, is a change of ether condition, commonly facilitates the production of fresh chemical compounds. And also pointing in the same direction, we have the fact that in many cases light, whose ether waves we have concluded produce atom explosion and ether liberation in bodies exposed to their influence, causes chemical change. Thus carbonic oxide, CO, unites with chlorine under the influence of sunlight to produce phosgene gas, COC1 2 .* In support of the explanation above suggested of the spontaneous chemical changes sometimes occurring when different substances are brought into contact : * According to the arguments above offered, we suggest that the steps of the process are as follow : 1. That in the presence of the chlorine the carbonic oxide has but half its normal volume, but one kind of atom being expanded, and that in this state it intermixes with chlorine, so that we have cO + Cl = OcCl. 2. That immediately on its production OcCl has its chlorine atoms condensed, taking the state of semi-expansion, OcCl, and that then a second intermixture with chlorine takes place : Occi + CUOcciCl. CAUSES OF CHEMICAL CHANGES. 373 First, with reference to the 1 suggested instrumentality of electrical action, we have the facts already referred to as to the spontaneous production of electricity on the contact of different substances, and we have also the important experimental fact, to which further reference will be made presently, that the intensest chemical action takes place between those bodies whose behaviour when exposed to an electric current would lead us to suppose that their ether emissions differ most widely i.e., between bodies one of which is highly electro-positive, the other highly electro-negative. And besides this general evidence we have some inter- esting examples of change of state produced in some bodies by the presence of certain other bodies in which the in- fluence of one body on the other seems evidently electrical. Thus, if a piece of zinc be suspended in a solution of lead acetate, lead crystals are successively deposited in a continuous arborescent form, so that the process presents the appearance of growth ; and if, instead of placing the zinc in the acetate, we place in the latter a piece of platinum wire, and place the zinc in a separate vessel containing dilute hydrochloric acid, and then connect the zinc and the plati- num, we have the same effect, so long as the latter continue in contact.* We suppose the decomposition of the lead acetate to be an intsance of electrolysis, i.e., of chemical analysis by means of an electric current,! and that the lead separates from the solution in a liquid state, but passes immediately into the crystalline state owing to its experiencing new ether conditions ; probably this latter change is due to a current of positive ether coming from the zinc. There are other instances of chemical change in which, * In the process of electro-plating and in the whitening of pins we have very similar effects, f Of this kind of analysis an explanation will be offered presently. 374 NEW THEORY OF CHEMISTRY. as in the case just mentioned, the body which sets up a reaction undergoes no alteration, and which we suppose to be due to electrical action. Thus hydric peroxide, HO (generally written H.^), is decomposed by the mere con- tact of many finely divided metals, and metallic oxides, without the latter undergoing any apparent change e.g., finely divided gold, silver, or platinum, procure an instant evolution of oxygen gas, and the finer the state of sub- division of the applied metal, the more rapid the decom- position. Such reactions are accompanied by great heat, and it is suggested that the cause of the decomposition of the peroxide is the expansion by heat of all the atoms of some of its molecules, this enabling the hydrogen atoms of these fully expanded molecules to combine with others which are but partly expanded, so that water is formed, and oxygen set free. This is expressed by the equation OH + HO = HOH + o. The supposition that the change is due to heat is sup- ported by the fact that hydric peroxide is an exceedingly unstable substance, and is readily decomposed by heat. As to the origin of the heat, it is suggested that electric action takes place between the finely divided metal and the peroxide, and that this produces great molecule destruction locally, which causes* the liberation of a considerable amount of unmolecular ethers, and, in consequence, the great rise of temperature observed. It may, perhaps, be regarded as in favour of the view that the action of the metals is an electric action, that the presence of a few drops of an acid i.e., of a compound in whose composition negative atoms predominate hinders the action of the electro-positive metal ; while the presence of an alkaline hydrate i.e., of a compound in whose com- position positive atoms predominate hastens the action. CAUSES OF CHEMICAL CHANGES. 375 In many cases where the decomposition of hydric peroxide is effected by metallic oxides, the oxides are themselves decomposed. Finally, as cases in which the coming together of electro- positive and electro-negative atoms may be supposed to produce electrical action and consequent heat and mole- cule destruction, we may refer to the fact that when finely divided platinum, known as platinum black, or what is known as spongy platinum, comes in contact with a mixture of the gases oxygen and hydrogen, the metal, though cold, causes the mixed gases to explode, and unite, forming water ; and to the analogous fact that crystals of iodine when applied to phosphorus which is exposed to the air cause its combustion. Next, showing the probable efficiency of the second cause of change of state above suggested, we have direct evidence furnished by another class of cases that mere contact of one body with another, in some cases, produces a quiet gradual change of state. Thus we have the familiar fact of water absorbing atmospheric air and holding it condensed, and also the facts that platinum and kindred metals (especially when finely divided e.g., spongy platinum or platinum black) have the power of condensing oxygen and other gases upon their surfaces ; finely divided platinum at ordinary temperatures absorbing about 240 times its volume of hydrogen; and finely divided palladium, at 200, nearly 700 times its volume of hydrogen. The condensation of atmospheric air by water i.e., in the language of our theories of change of state, the passage of the minima values of the fluctuating density and cohesion of those atoms in the oxygen, nitrogen, and other gases composing the atmosphere whose expansion produces the gaseous condition, past the respective critical values at which, in these different gases, the cohesion 376 NEW THEORY OF CHEMISTRY. becomes high enough to prevent the existence of expansive force in such atoms we are disposed to attribute to an increase of intermolecular pressure caused by the presence of the water, and due to a greater amount of explosion of primary atoms, and consequent ether liberation, proceeding among the molecules of water than among the molecules of the gases composing the atmosphere.* The condensation of gases by platinum, and other kindred metals, we are disposed to attribute to great density of the unmolecular ethers of these bodies, which we suppose subsists,! the dense unmolecular matter raising the minima values of the fluctuating local density and cohesion within any particles of gas coming into very close proxi- mity to the metals emitting it. A reference to one or two familiar examples of synthesis, and of metathesis, to which the above theory of the origin of spontaneous combination will apply, may in this place be instructive. The two gases ammonia, H 3 N, and hydrochloric acid, HC1, when they meet in the same receptacle combine and produce a crystalline solid, ammonic chloride, H 4 NC1. Our theory of this change is that as a first step the fully expanded gases, HNH 2 , HC1, through contact with one another, both experience a change of state to a condition of half-expansion ; HNH 2 perhaps passes to the condition NH 3 , and HC1 to the condition HC1 ; that next the two denser gases thus produced, being each capable of inter- mixture through having but one kind of atom expanded, symmetrically intermix. * As already stated (pp. 35 and 326), we suppose that pressure adequate to convert bodies from the gaseous to the liquid or solid states is furnished by the expansion of ether liberated by molecule destruction. f Their high specific gravities are in harmony with this sup- position (see p. 49). CAUSES OF CHEMICAL CHANGES. 377 Thus NH 3 + HC1 would produce NH 4 C1. And that finally the change in the ether conditions produced during the act of intermixture causes a further change of state, so that the ammonic chloride directly it is found in the gaseous state, passes to the liquid state, and thence to the state of crystallization. As a second example we have the combination of nitric oxide with oxygen, which has been already referred to (p. 362). In this synthesis the occurrence of molecule destruction to which, probably, we may refer the condensation which brings about change of state, seems indicated by the heat produced, of which the momentary expansion when the gases first meet is evidence. It may further be noticed that if our conclusions as to the origin of colour are accepted (see p. 258), we have evidence, in the deep red tint of the nitric peroxide vapour, of the continuance of considerable atom explosion in this compound after its formation. As a third example : Brass tinsel, that is to say tinsel composed of an alloy of copper and zinc, being exposed to chlorine gas, chemical union at once takes place, the product being a mechanical mixture of cupric chloride and zincic chloride ; so much heat is produced that the tinsel becomes incan- descent. The two similar reactions which occur are expressed in symbols thus : Cu + 201 = CuCl 2 , Zn + 201 = Zn01 2 . Taking the first of these, the explanation suggested is : That since of the three bodies coming together, copper, zinc, and chlorine, the zinc is highly positive and the 378 NEW THEORY OF CHEMISTRY. chlorine highly negative,* minute electric currents are produced when the contact takes place which cause accumulations of the unmolecular ethers and consequent heat (see p. 319). That these ether accumulations cause molecule de- struction which, at first insignificant, becomes more and more violent as ethers liberated by it accumulate, this being evidenced by the incandescence of the metals (see p. 260). Perhaps the molecule destruction is facilitated by the difference in readiness of compression of the different kinds of atoms causing them to vibrate out of harmony. That the heat produced by the presence of the un- molecular ethers which thus accumulate expands the atoms of copper, upon which these atoms symmetrically intermix with the expanded chlorine atoms, and we have Cu + Cl = CuCl. That as the temperature begins to fall the fully expanded atoms, CuCl, thus formed, pass to a state of semi- expansion, and then take part in a second symmetrical intermixture with chlorine atoms, so that we have CuCl + Cl = CuClCLt And as a final step ; that, as the temperature falls still * See Berzelius's series (p. 393). t It may be that the chlorine not the copper atoms are expanded in the molecules of CuCl, but as in this case the atoms intermixing would be of the same kind, we should then have to suppose that different ether conditions were prevalent among the atoms of chlorine in the molecules, CuCl, from those prevailing among the atoms of chlorine in the chlorine gas, productive of different readiness of compression in the two sets of atoms, for without the latter condition the law of symmetrical intermixture would not be in force. That atoms of the same kind are sometimes sym- metrically intermixed we have already concluded from the case of ozone (see p. 367). CAUSES OF CHEMICAL CHANGES. 379 further, the gaseous cupric chloride thus formed passes through the liquid to the crystalline state. Supporting the above suggested explanation we have the fact that if cupric chloride, CuCl 2 , is heated it fuses, and at a red heat gives up half its chlorine, so that cuprous chloride, CuCl (commonly written Cu 2 Cl 2 ), remains. For evidently we may regard this as the converse of the above, and, in accordance with the theory of analysis above suggested, suppose that the breaking up of the cupric chloride by heat is due to all three atoms in each molecule, CuCl 2 , expanding when a sufficient rise of temperature has taken place ; the law of symmetrical intermixture thereupon separating the unsymmetrical mass into masses of symmetrical cuprous chloride gas and chlo- rine (see p. 355). Thus : CuClCl = CuCl + Cl. The explanation of the similar reaction between the zinc and the chlorine will be very similar. As a fourth example we may take the combination of a solid with a liquid : Sodium monoxide, Na 2 0, com- bines with water, H 2 0, producing sodium hydroxide, NaOH. In this, as in the last example, we may suppose that, when the different atoms come together, electric action, molecule destruction, and heat are produced, so that both bodies are vaporized, and that the result is that in the sodium monoxide molecules the two atoms of sodium, and in the water molecules the two atoms of hydrogen, are expanded. As both kinds of molecules will, if this be the case, have but one kind of atom expanded, we may conclude that symmetrical intermixture will thereupon take place between them. 380 NEW THEORY OF CHEMISTRY. Thus, if we write each kind of molecule to contain but one expanded atom, we have NaJ + H = NaoH. i 2 As before, we suppose the final step, which immediately follows, to be the passage of the symmetrical gas thus formed, through the liquid, to the crystalline state. As a fifth example : If a current of chlorine be passed through a mixture of crushed ice and water, the definite hydrate C1 2 ,10H 2 is obtained in a crystalline state. Here the first step would, according to our theories, be the symmetrical intermixture of aqueous vapour having two atoms of hydrogen expanded in each molecule, with chlorine. Thus, writing the molecule of water to contain but one expanded atom, We suppose the intermediate compound thus produced, immediately on its production to change its state to a condition of half-expansion, ClH , and then to intermix with a further molecule of water. Thus : As before, we suppose a change of state thereupon occurs, making a third intermixture with gaseous water molecules possible. ClH,0 + H^ = HH,^ Cl, and so on till we reach the intermixture, ^ + H = HHAC1. CAUSES OF CHEMICAL CHANGES. 381 Finally we suppose that : the last-named compound, which may be written, C1 2 ,10H 2 0, when formed instantly passes to the liquid, and thence to the solid state without affording opportunity for further symmetrical intermixture. Of reactions in which one compound appropriates a portion of another, we may take one of those cases in which sulphur trioxide, S0 3 , readily parts with one of its atoms of oxygen to another compound. If sulphur trioxide and phosphorus trichloride are mixed together at a normal temperature the trioxide loses one of its atoms of oxygen, which is added to the tri- p chloride forming phosphorus oxychloride, OC1 3 .* Probably the nature of this reaction is expressed thus : | 01, + SOOO = Cl| Cl 01, + SOOO = Clci 2 O + SOO. A strong red heat is ordinarily necessary in order to resolve sulphur trioxide into the dioxide and oxygen, and the conclusion to which we are led is that, in the above case, such a heat is produced by the electrical action, and the consequent atom destruction, taking place when the two compounds are brought together. Next as an example of metathesis : If a piece of sodium be brought in contact with water, upon which it floats, the sodium fuses, vigorous chemical action ensues, hydrogen is evolved, and solid sodium hydroxide (caustic soda), NaOH, is formed. Here we have the highly positive element sodium coming in contact with the less positive water molecules, and, as in the case of the above combination of sodium monoxide and water to produce sodium hydroxide, we suppose that electrical action is set up which produces rise of temperature and initiates molecule destruction. * As to the atomic weight of phosphorus, see Note , p. 345. 382 NEW THEORY OF CHEMISTRY. Upon this we suppose that the heated sodium partially vaporizes so that we have sodium vapour in contact with water vapour, and that, in accordance with the above theory of metathesis (see p. 358), the expanded atoms of hydrogen and oxygen and the expanded atoms of sodium all become mixed together where the boundaries of the vapours of water and sodium meet. And we suppose, finally, that a greater difference in readiness of compression subsisting between the expanded oxygen atoms and the expanded sodium atoms than be- tween the former and the expanded hydrogen atoms, symmetrical intermixtures of sodium and expanded hydro- gen dioxide OH are formed and the expanded hydrogen atoms isolated. This process would be expressed as follows : Na + HOH = NaHOH = NaOH + H. If instead of sodium we use the metal potassium a precisely corresponding reaction takes place, but in this case the heat produced is adequate to inflame the dis- placed hydrogen,* which combines with the oxygen of the atmosphere to form water. To explain this in terms of our theories : We suppose that when potassium is employed, the quantity of inter- mixed ethers accumulated is sufficient to produce a high initial expansion of the liberated hydrogen and of the oxygen of the atmosphere present at the place of the reaction, and also much molecule destruction and conse- quent ether liberation ; that as the hydrogen is liberated, it therefore expands to a highly tenuous state, and while in this state symmetrically intermixes with oxygen similarly expanded.f Finally that, certain of the atoms becoming * Combustion is referred to subsequently, t See Note *, p. 348. CAUSES OF CHEMICAL CHANGES. 383 condensed by pressure arising from the ether liberation, the further intermixture necessary for the production of water follows. The two intermixtures supposed to occur are, H + o = HO, HO + H = HOH. Another simple metathesis, of which a similar explana- tion is offered, occurs when sodic hydrate, the product of the metathesis just dealt with, comes in contact with a solution of hydrochloric acid,* a mixture of common salt and water being then produced. We suppose that the hydrochloric acid, half of whose atoms consist of the highly negative element chlorine, emits more negative ether than the sodic hydrate does, that therefore when the bodies come together, we have, as before, electrical action, heat, and molecule destruction, resulting in the expansion of several kinds of atoms to the gaseous state ; and that the rearrangement which follows is, as suggested in other cases, due to the different readi- ness of compression of different atoms. The supposed steps of the process would be written, NaOH2+ HC1 = NaOHClH = NaCl + HOH, the molecules OH, which when met with alone are known as hydric peroxide, passing unbroken through this as through the former metathesis. We may mention next a group of metatheses which are instructive as furnishing a probable example of successive steps of metathesis analogous to the successive steps of synthesis by which we have supposed complex compounds are built up. * Some special reference is made to acids in a subsequent chapter. 384 NEW THEORY OF CHEMISTRY. When chlorine and methane, CH 4 , are mixed and exposed to diffused light (explosion takes place in direct sunlight), the whole series of derivatives, monochloroniethane, CH 3 C1 ; dichloromethane, CH 2 C1 2 ; trichloromethane, CHC1 3 ; and tetrachloromethane, CC1 4 , are formed, the displaced hydro- gen combining with chlorine and producing hydrogen chloride, HC1. Perhaps the following are the successive metatheses : CH 3 H + 2C1 = CH 3 C1 + HC1, CH 2 C1H + 2C1 = CH.C1C1 + HC1, CHC1 2 H + 2C1 = CHC1 2 C1 + HC1, CC1 3 H + 2C1 = CC1 3 C1 + HC1. But possibly some of the compounds may arise differently, thus : HH + 2C1 = HHCl + Cl = Hd + Cl = H^Cl + HC1, and Cl^H + H^H = HCH.CI. , t Z We may mention, finally, a metathesis which goes to show that atoms sometimes preserve their characteristic individual properties when they are combined with other atoms ; i.e., that we may have the effect of particular groups of atoms on other particular groups not altered by tlie presence of other atoms in combination with one kind of these groups. If a solution of hydrochloric acid be poured upon sodic carbonate (common soda), a violent effervescence takes place, carbonic dioxide, C0 2 , is liberated, and the other products of the reaction are found to be common salt and water. Except that other atoms are present, which, when the expansion to gas occurs, segregate by themselves, it seems CAUSES OF CHEMICAL CHANGES. 385 evident that this metathesis may be regarded as of the same nature as the reaction between sodic hydrate and hydrochloric acid above referred to, the process being expressed by the equations CO^NaAoOHu + 2HC1 = COO + 9HOH + 2NaOHClH = COO + 9HOH + 2NaCl + 2HOH. To render our theory of chemical combination complete we suppose : That for gaseous mixtures to have the stability without which intermixture will not result in chemical union, but will continue mere intermixture, they must have a greater expan- sion at the moment the intermixture takes place than subse- quently * For, if this is the case, a minimum mass f of the com- pound after intermixture has taken place will exceed in magnitude one of the combining molecules, consisting of an expanded secondary atom and its proportion of condensed atoms, if such are present, and, consequently, the internal motions occurring in every mass, which tend to separate particle from particle, will not be able to separate any portion of it into distinct atoms, or molecules. In support of this supposition we have the well-known fact that heat, an agent which produces expansion, is always found where there is chemical change, and further, which is still more direct evidence, we have the fact that in many cases very great expansion is found to occur at the moment when a chemical change takes place notably in the case of explosions. J * This has been already suggested of compound gases of two atom molecules whose volume is the sum of the gaseous volumes of their components (see Note *, p. 348). t See p. 9. J We shall, however, conclude subsequently that explosions are not entirely due to sudden gaseous expansion. 25 38G NEW THEORY OF CHEMISTRY. In harmony with this, we suppose that the passage of the electric discharge produces chemical combination in so many cases owing to its power of producing great atom expansion. Thus, when nitrogen and ethine gases mix at ordinary temperatures under normal conditions we have mere inter- mixture, but when electric sparks are passed through the mixture hydrocyanic acid is formed CH* + N = CNH. Consistently with the above, we suppose that when compounds decompose directly they are expanded to the gaseous state, it is because the conditions are such that they reach, and continue at a degree of expansion as great as that at which their formation took place. One word in closing this chapter on the subject of quantivalcncCj as it is called. When two different kinds of secondary atoms, or secondary molecules are brought together, and chemically combine, they, in the greater number of instances, do not form a stable compound of an equal number of each kind, but of different definite simple proportions of the two kinds. Taking the combination of atoms, for instance, we have as stable compounds H 2 0, H 3 N, H 4 C, CrF 6 . Further, when we compare many different combinations, we find a striking approximation to the general law, that comparing the quantities of different elements combining with the same element or compound to produce stable compounds, the atoms of the various elements have certain different proportionate values for combining purposes the relative valency of hydrogen, oxygen, nitrogen and carbon being, for instance, expressed by the figures 1, 2, 3 and 4 respectively. * Ethine is generally written C 2 H 2 , on account of its having the volume expressed by CH. QUANTIVALENCE. 387 Thus when one atom of carbon will effect a stable com- bination with some given atom or group of atoms, it is generally found that, if hydrogen will combine with the same atom or group of atoms, four atoms of hydrogen are requisite to form the corresponding stable compound. The law just referred to, which however is only a very partial one, is called the law of quantivalence^ and its existence has led to an endeavour to frame a table of relative quantivalence, in which the various elements are called monads, dyads, triads, etc., as one of their atoms is equivalent for combining purposes to one, two, three, etc., atoms of hydrogen. We here subjoin a table of quantivalence taken from the "Encyclopaedia Britannica," Art. "Chemistry," p. 473, in which a number of the elements are arranged mostly according to their apparent maximum valency. Monads. Dyads. Triads. Tetrads. Pentads. Hexads. Hydrogen Fluorine Oxygen Barium Boron Gold Carbon Silicon Nitrogen Phosphorus" Sulphur Selenium Chlorine Strontium Tin Arsenic* Tellurium Bromine Calcium* Lead Antimony Tungsten Iodine Magnesium Aluminium Bismuth Molybdenum Potassium Zinc Indium Sodium Cadmium Thallium Lithium Copper Iron Silver Mercury* Chromium Manganese Cobalt Nickel Platinum Palladium Now as to the direction in which we must look for an explanation of the facts of quantivalence : We have con- cluded that the relative numbers of the different kinds of atoms which will combine in any given instance of chemical action will depend on how many successive symmetrical * This table is not corrected to show the true position of those elements which are believed to have different atomic weights from those usually received (see p. 345). 388 NEW THEORY OF CHEMISTRY. intermixtures take place ; and we have also concluded that further symmetrical intermixture is possible in any given case only when the product of the last previous inter- mixture passes into a state in which but one kind of atom is expanded. Again, we have argued that the state of a mass ; i.e., whether it shall be gaseous, liquid, or solid, and, if gaseous, how many atoms it shall have expanded; depends not only on the outward conditions prevalent, but also on the nature of the ether emissions of the atoms themselves. Therefore the valency of any particular element, or compound may be expected to depend chiefly on the nature of its ether emissions, to be, in fact, an index of the potency of these ether emissions to cause change of state of masses of atoms of which the element or compound forms part. Probably this is sufficient to account for the degree of regularity of behaviour of the different elements revealed by the facts of quanti valence.* And it is an explanation which seems to be countenanced by the fact that commonly the quantivalence of a radicle, or compound is found by deducting the quantivalence of the negative atoms from that of the positive, or vice versa. Deferring for the moment the consideration of the dis- tinguishing features of acids, alkalies, and salts we shall in the next chapter devote a few pages to the subject of electrolysis. * Variations of external conditions commonly produce more or less variation of valency, especially in the case of organic com- pounds. 389 CHAPTER XXXV. ELECTROLYSIS. WE have supposed (p. 359), that there is a possibility that in some cases chemical analysis is caused by atoms being shaken out of a mass while they are in a con- densed state, instead of by their being separated through the action of the law of symmetrical intermixture exerted on them and on other atoms with them while in a state of gaseous expansion. We shall now offer an explanation of the kind of analysis known as electrolysis, based on some such conception, this kind of analysis, according to the theory we shall offer, not being preceded by momentary expansion of some of the atoms concerned to the state of gas, as we have supposed to be the case in other instances of analysis. The most familiar example of electrolysis the decom- position of water by the electric current is exhibited as follows : A cell is filled with water, slightly acidulated with sulphuric acid to improve its conducting power ; two strips of platinum immersed in the water and in proximity to each other are respectively connected with the two termi- nals of a voltaic battery, so that the positive electricity disengaged at one pole passes from one of the strips of platinum to meet the negative electricity disengaged at the other which passes from the other strip. The effect on the liquid is that bubbles of gas are found to be collecting upon each of the strips, and when means are taken to collect 390 NEW THEORY OF CHEMISTRY. these bubbles, it is found that those from the positive pole consist of oxygen, those from the negative pole of hydrogen, and that the quantities of the two gases liberated bear the same proportion as that in which these two elements combine to form water. The theory of electrolysis suggested here is as follows : In consequence of the different readiness of compression of the different kinds of secondary atoms composing a chemical compound, these atoms, it is submitted, when the compound is in the liquid state, tend from time to time to take up as symmetrical a relative arrangement in space as possible," but as the conditions can never be such that absolute symmetry is attainable, and as moreover these conditions are varied locally to a slight extent by every passing wave-disturbance, the process never results in complete equilibrium, and the atoms continually perform inconsiderable motions with respect to one another.f Now, from our arguments respecting electric conduc- tion, we conclude that the moving unmolecular ethers, whose passage in opposite directions constitutes an electric current, have different degrees of cohesion to different secondary atoms among which they are flowing, according to the kind of ether which the various atoms are emitting through the destruction of some of their primary atoms that the moving positive ether lays a firmer hold of the secondary atoms from which most positive ether is being emitted, the * The nature of the different symmetrical arrangements towards which different classes of compounds tend e.y., the nature of the symmetrical arrangement of the atoms of oxygen and hydrogen in water will be considered in a subsequent chapter on crystal- lization. t We do not suppose that the continual shifting of the relative position of the different secondary atoms caused in this way is sufficient to produce any appreciable rupture of their continuity, but that one atom slides on another. ELECTROLYSIS. 391 moving negative ether a firmer hold of those from which most negative ether is being emitted.* Therefore, in any slight rearrangement of atoms from time to time occurring, as just explained, some atoms have a greater disposition to move their position towards one pole than in any other direction, and others a greater disposition to move theirs towards the opposite pole than in any other direction ; and as a consequence of this we have some atoms shaken, as it were, out of the intermixture towards one pole, and other different atoms shaken out towards the opposite pole, the bulk of the atoms in the meantime continuing to occupy a practically identical symmetrical disposition of their different kinds. And finally, as a consequence of the intermixed atoms thus preserving the same symmetrical arrangement, and therefore practically the same proportions of the different kinds, the number of atoms shaken out of intermixture at one pole is complementary of the number of different atoms shaken out at the other pole ; Le., the proportions of the different atoms liberated are those subsisting in the com- pound electrolysed. The following facts with regard to electrolysis support the theory which has just been stated. (1.) Bodies capable of electrolytic decomposition are fluids. (2.) No alteration takes place in any part of the fluid electrolysed except at the two terminals or poles of the battery. (3.) The quantity, that is the mass, of the electrolyte decomposed is proportional to the quantity of electricity which passes through it. In other words, it is jointly proportional to the strength of the current and the time that it lasts. * That positive ether holds most continuously to positive, negative ether to negative, see p. 66. 392 NEW THEORY OF CHEMISTRY. (4.) The two primary products of decomposition do not appear together, but one appears at the positive the other at the negative pole, and they appear in the same propor- tions as those in which they subsist in the undecomposed electrolyte. (5.) The quantities of different electrolytes decomposed by the same quantity of electricity are in the ratio of their chemical equivalents (see p. 386), or, to state the case in the language of the theory above submitted, if two different electrolytes have their constituents successively subjected to the action of the opposite drawings of the same quantity of moving etheis i.e., the same electrical current it is found that the respective quantities of the electrolytes thus drawn out of the molecular combination are in such pro- portions as would take part in " double decomposition" between themselves.* The following definitions were invented by Faraday, who first established the laws just referred to. (1.) As already stated, the substance decomposed is called an electrolyte, and the process of decomposition is called electrolysis. (2.) The two portions into which the electrolyte are primarily divided, no matter how complex, are called ions ; that disengaged at the positive pole is called the anion, that disengaged at the negative the cation. Thus, in the instance of decomposition of water, the oxygen is the anion, the hydrogen the cation. (3.) The poles in the electrolyte are called electrodes, that at which the anion is disengaged is called the anode, that at which the cation is disengaged the calliwlr. It is evident that the course taken by different elements * Prof. F. Kohlrausch of Wurzburg has shown that in diluted solutions of salts, including hydrates of acids and hydrates of caustic alkalies, every atom under the influence of currents of the same density moves on with its own peculiar velocity. ELECTROLYSIS. 393 with respect to each other, when they are set free from a compound submitted to electrolysis, may be expected to furnish some information as to the relative ether constitu- tion of such elements. Suppose, for example, that, as in the case of water, there are but two elements, one passing towards the negative, the other towards the positive pole, it may reasonably be concluded, if our foregoing theory of the process be a correct one, that the element which passes towards the positive pole (the oxygen in the case of water) has more negative ether among its primary atoms than has the element which passes towards the negative pole (the hydrogen in the case supposed). The view once held by Faraday, that a given element is unalterably either an anion or a cation, has been disproved by the fact that the same element may act as an anion in one solution and as a cation in another ; but an attempt has been made to arrange the elements in a series such that in a compound of an element A with any one of those above it, A would appear as a cation, but in a compound with any of those below as an anion. Of any two elements the one which stands first in such a series (being that more ready to pass towards the positive pole, i.e., according to our theory, to travel with the negative ether of the current) is called more electro-negative, and the other element (which passes more readily towards the negative pole, i.e., with the positive ether of the current) is called more electro-positive. The electro-chemical series as determined by Berzelius is as follows.* Electro-negative. Oxygen Bromine Molybdenum Sulphur Iodine Tungsten Selenium Phosphorus Boron Nitrogen Fluorine Arsenic Chromium Carbon Antimony Chlorine Vanadium Tellurium * Taken from "Enc. Brit.," Art. "Electrolysis/' p. 112. 394 NEW THEORY OF CHEMISTRY. Tantalum Titanium Silicon Hydrogen Gold Osmium Indium Platinum Rhodium Palladium Mercury Silver Copper Bismuth Tin Lead Cadmium Cobalt Nickel Iron Zinc Manganese Uranium Cerium Thorium Zirconium Aluminium Didymium Lanthanum Yttrium Glucinum Magnesium Calcium Strontium Barium Lithium Sodium Potassium Electro-positive. We may urge upon the reader that the behaviour of the different elements which allows of the formation of such a series furnishes strong testimony in favour of the views which have been submitted as to the ether structure of the elements. Before concluding these few remarks on electrolysis, we may just mention one or two additional facts. The separation of several metals from their oxides was first accomplished by means of electrolysis, the metal, in the case of decomposition of such binary compounds, always passing to the negative pole. When more complex substances are decomposed by electrolysis, the primary separation into two constituents is often followed by secondary actions. For instance, sodium sulphate is presumably first divided so that sodium (Na 2 ) passes to the negative pole, and sulphur and oxygen (S0 4 ) to the positive. But the liberated sodium at once unites with the oxygen of the water, and so liberates hydrogen, and the sulphur and oxygen produce sulphuric acid at the negative pole, liberating oxygen. And as another instance. When potassic carbonate (K 2 C0 3 ) gives up potassium at the negative pole, and the atomic aggregate, C0 3 , at the positive, the potassium instantly combines with the molecules of water, and the ELECTROLYSIS. 395 aggregation, C0 3 , is resolved into a mixture of carbonic dioxide, C0 2 , and oxygen. The conditions requisite in an electrolyte to insure con- duction are, according to our arguments, molecular, and it would appear that some degree of irregularity in the disposition of the molecules favours conduction. Thus, two non-conductors, as water, HOH, and hydrochloric acid, HC1, on being mixed, form a very good conductor. The peculiar molecular state of some of the elements liberated by electrolysis may be referred to. Thus oxygen partly takes the shape of ozone. The molecular state of the deposit of metals effected by electrolysis varies very much with the density of the current. Thus, when the density of the current is small, metals are deposited in crystals ; when it is increased they take a form similar to that of melted metal ; and when the density is great the deposit is amorphous, botryoidal, or pulverulent. The metal separated from an electrolyte commonly alloys with the metal of the electrode to which it passes. Thus copper deposited upon platinum alloys with it to a certain extent, the alloy penetrating to a considerable depth ; and the same occurs in the case of the electrolysis of many metals and salts with mercury electrodes. Still more noteworthy is the combination of liberated gases with an electrode, e.g., oxygen or hydrogen become condensed (liquefied) and pass into the substance of a platinum electrode. Root has found that in some cases the gases thus alloying an electrode of platinum penetrate it and appear at the opposite side to that at which they enter. Some interesting observations have been made on the motion of solid particles and other bodies in fluids of high resistance ; perhaps a careful examination of the motions of such bodies would throw light upon the relative distri- bution of the two opposite currents of the two ethers whose motions constitute an electric current. PRINTED BY HAZELL, WATSON & VINKY, LIMITED, LONDON AND AYLE8BVRY. 13"?ar'62DS AU6 I '! I j