state, and then to pass away from matter into æther, in the act of generating ætherial undulations, which are carried off presumably ad infinitum, through the inter-stellar and extra-galactic spaces. To render these conceptions clearer, let us apply them briefly to the existing state of our own solar system, with special reference to the planet on which we live. Here we have a central mass in a state of radiant heat;. that is, of rapid molecular kinetic energy, caused by the precipitation of atoms out of which it has been aggregated. As these atoms have collected round their centre, their energy of passive separation has been exchanged for that of heat. The rapidly vibrating molecules are now, and have ever been, constantly giving off to the surrounding æther waves of energy, which are passing away into the space on every side in ever-widening concentric spheres. Simultaneously with this loss of energy, force is perpetually drawing in its skirts and lessening its diameter. Some ninety odd millions of miles away from it is a lesser mass, of about 1.100.000th of its volume. This lesser mass was once, like the greater, a source of radiant heat; but now it has radiated away the greater part of the energy from its superficial molecules, though those of its centre are still probably in rapid motion of heat, and occupy far more space than they would do in a state of quiescence. Of course this central energy is still escaping, though slowly. On the surface, as energy has radiated, force has built up most of the atoms into compound molecules, and most of the molecules into solid coherent bodies. But a minute portion of the energy which is ever escaping from the sun in the abovementioned concentric waves, falls upon that part of the earth's surface which is from time to time turned towards it in the course of each diurnal revolution. Here it occupies itself in working out local separations, which slightly counteract the effect of those forces which have been slowly engaged in aggregating the matter of the earth. Falling upon the atmosphere, it causes separation of its atoms of the nature of heat (though by convection only); and hence result the phenomena of that enlargement of its volume which is known to us through trade winds, monsoons, &c. Falling upon the ocean, it prevents it, in tropical and temperate latitudes, from freezing or assuming the aggre gated solid state; and it raises large masses of its surface, as vapour, to a considerable height; which masses, there losing their energy once more by radiation, are again precipitated on the surface as rain. Falling on the solid land, it exhibits its separative power, by disintegrating the stable compounds which it finds there, and either reducing them to their elements, or rebuilding them in less stable combinations; among the most noticeable of which are those composing animal and vegetable organisms. Finally, falling upon the molecules of matter in certain special conditions, it produces that electrical separation, the reaction from which is known to us as thunder and lightning. And here we see how it is that energy, really equivalent to disjunctive power, has come to be considered chiefly from the purely anthroponistic point of view, as that which "performs work." Being ourselves small collections of atoms, bound together in unstable combination, on the outer crust of the earth, we direct our attention chiefly to those little changes which are effected amongst its superficial molecules. We see that if it were not for this reflected energy, borrowed from the sun, hardly any changes would take place upon the earth. A very few unusual phenomena, such as those of earthquakes, volcanoes, and geysers, are due to the slow escape of the earth's internal energy, and the consequent collapse of the superficial crust through the force of gravitation. But all the common phenomena of every-day life-winds, rivers, combustion, animal and vegetable growth-are due to the energy which falls upon the earth from the sun. Thus the practical consideration of energy as that which performs work, overlies the theoretical consideration of it as separative power. But if we look closely into the matter, we shall see that force is just as much requisite for the performance of work as is energy. In a single-action steam-engine, the gravitation which pulls down the piston when it reaches the deadpoint, is as necessary as the heat which elevated it to that point: and the attractive force of chemical affinity which draws together the atoms of carbon and oxygen, is as necessary as the energy of passive separation which before divided them, or that of molecular motion into which it is transformed in the boiler: in short, in every case it is the interaction of the two powers which performs the work. What, then, becomes of the energy which is intercepted by the earth on its transit through space? Is it retained here permanently, or does it, like other energy, tend to be diffused through the ætherial medium? In answering this question we must remember three points: first, that its total quantity is relatively small (only 2.000.000.000th of the whole amount emitted); second, that it affects only the superficial molecules; and third, that a large amount of it is immediately returned, and only a small portion works changes of a chemical, electrical, or organic sort upon the earth. Every twenty-four hours the heated sides of the world are turned away from the sun to the comparatively unenergetic æther on the remote side, and give off the greater part of the heat they have received during the day. In Sahara, where few organic changes occur, and there is little vapour of water in the atmosphere to retain the heat, the whole amount received during the day is transferred so rapidly at night, that ice has been known to form. Elsewhere the heat is also given off, though less conspicuously. But a small remnant of radiant energy has been transformed during the day into energy of visible and of chemical separation, in the decomposition of certain stable compounds, which reappear in the unstable forms of hydrocarbons and other constituents of living organisms, and are raised in the plant, the tree, and the animal, to a position of visible elevation above the mass of the earth. Organic life, then, must be viewed as a local interruption of that process of integration which force is everywhere bringing about on the earth, the solar system, and the kosmos at large. And here I must venture to differ, with all deference and humility, as a scholar to a master infinitely his superior in knowledge and grasp, from Mr. Herbert Spencer, to whom I need hardly acknowledge my obligations, so obvious are they throughout. Mr. Spencer regards the living organism as an instance of integration: I must rather consider it as an essentially transitory case of disintegration. Solar energy unlocks the elements bound together by chemical affinity in the atmosphere, the rocks, and the water; lifts them up to a height of visible elevation above the earth's surface, and endows them with actual motion of sap and blood, of limb and muscle. Let us see in detail how this is effected, remembering always that energy exists in chemical elements in a state of separation; while, in the state of combination they have yielded up their energy, and are locked together by the force of affinity. If we were to shut a man up in an air-tight room for twenty-four hours, and supply him with food; at the end of that period, when he had eaten all the food and breathed all the air in the room, it would still contain all the chemical elements which it originally possessed. Yet the man could not continue to live for an indefinite period under such circumstances. And why? Because life is a manifestation of energy; and though all the matter is there still, all the energy has been given off as heat, and is being radiated into space. Carbonic anhydride, a relatively stable unenergetic compound, now replaces the free oxygen of the atmosphere and the comparatively unstable carbon of the organism. The energy of chemical separation, which they possessed in their uncombined state, has been dissipated as molecular motion.* In order to re-energize the elements and continue the man's life, vegetables must be introduced into the room: solar energy must be allowed to act upon them; that energy must, in their leaves, once more deoxidize the carbonic anhydride; or, in other words, produce energy of chemical separation between the carbon and the oxygen: the man must eat and digest the vegetables, and a second time combine the carbon with the freed oxygen: heat, and all the phenomena of animal life, must thus be produced; and so on ad infinitum. But a perpetual renewal of energy is necessary for the continuance of these processes. The leaves of the plant fall and are withered; decomposi * Or rather, some portion of it; for a part is re"latent heat.” tained in the compound form, as When we speak of stable and unstable compounds, we mean those which have retained relatively small or large amounts of energy. So much is occasionally retained, that a very small extra integration of energy is sufficient to overcome the affinities. Becquerel found instances where compound bodies, "whose constituents were held together by feeble affinities, such as iodide of nitrogen, were decomposed by the vibration occasioned by sound." (Grove, Correlation of Physical Forces," 4th edition, p. 133.) So the formation of an unstable from a stable compound is a case of the integration of energy; while, in the passage to a stable from an unstable one, energy is dissipated. tion sets in; the unstable compounds give place to more stable ones; and the contained energy is liberated as heat, to find its way at last to that interstellar limbo, whither all the energy of the kosmos is tending. Similarly with the animal: it is perpetually disintegrating and giving off its chemical constituents in more stable forms; heat replaces the chemical separation; and that heat, like the other, goes off to increase the "great waste-heap" of the universe. And, sooner or later, plant and animal die: the elements composing them are set free; new compounds are formed and again the energy is dispersed into space. But day by day new energy is imported from the sun to effect the same changes over again and day by day the old energy, that has done its work here, is turned loose upon the æther, to diffuse itself for ever towards infinity. : : But not quite all of it at present. Some small portion remains here, locked up for a time in air and water, in wood and coal, as potential energy of the atomic kind. We may explain this peculiar fact by the analogy of molar energy in a stone. If I lift a stone to the top of a wall, it may either topple over at once, in which case its potential energy is converted first into kinetic molar (actual motion), and then into heat; or it may, if placed in equilibrium, stand there for an indefinite period, its energy remaining all that time of the potential sort, because the force of gravitation is counterbalanced by that of cohesion. Somebody must give it a push before it can tumble off. Just in the same way, energy may separate chemical compounds, and build them up into the isolated forms of diamond or charcoal, of pure iron or free oxygen: and then these bodies, possessing energy of chemical separation, may remain in that uncombined state for a considerable length of time, under favourable circumstances. A piece of pure phosphorus is in the condition of the stone left to support itself in the air: the moment it comes into contact with oxygen, it combines with it, and gives off its chemical separation as radiant energy. But a piece of charcoal is in the condition of the stone perched on the wall; it will not combine with the oxygen if left to itself. So, when you bring together the free oxygen and the charcoal and ignite them, you do something which is in some way the analogue of pushing over the stone; and then force draws together the two into carbonic anhydride, while the energy is given off again as heat. Thus, sooner or later, even in these exceptional cases of stored-up energy, force ultimately wins the day, and the disjunctive power follows all its kind through the ætherial medium. Just at the present stage of the world's history, we are busily engaged in so dispersing the vast stock of energy laid up for our use in the carboniferous period. The sun's rays at that time de-oxidized large quantities of carbon and hydrogen, built them up into trees, and left in them a store of energy in the form of chemical separation. When these trees fell, they would in ordinary circumstances have decayed; that is, would have united with the atoms around them for which they had affinities, and have given off their energy to surrounding space. But, falling under water probably, they were isolated from any free oxygen with which they could combine, as is now the case in the bogs of Ireland; they were then compressed under superincumbent strata; and have thus been preserved to our day as "bottled sunshine," constituting vast reservoirs of available energy. But if combustion be essentially a body parting with its energy under the force of chemical attraction, how comes it that before combustion can be set up, fresh energy from outside must be integrated? As the carbon and oxygen are placed in juxtaposition, why do they not immediately combine in the case of coal, as in the case of animal organisms? This seeming paradox may be explained again by the analogy of the stone on a wall; its potential energy cannot be converted into kinetic, unless energy from without, such as a push with the hand, or a puff of wind, give it a start. Otherwise, it is not brought within the sphere of possible action of the force which affects it, namely, gravitation. Now we must remember that chemical affinity is a force acting only through very small distances. Let us illustrate this by the case of cohesion. If a piece of iron be left freely suspended in the air, it will fall to the earth under the pull of gravity, no matter what distance may separate them; because gravity is a force which acts through relatively great spaces; but if two pieces of iron be placed together, they will not cohere unless absolutely smooth, because cohesion is a force which acts through relatively small spaces. If, how ever, we heat the two pieces, then the motion of their molecules brings them into such close contact, that as they cool down they cohere perfectly. Similarly with coal and oxygen; we may suppose that they never approach near enough to one another to come within the sphere of their mutual attractions. But when we bring them under the influence of heat from another source, we may imagine that the atoms are so far agitated as to come within that sphere; and then they rush together with that immense disengagement of radiant energy with which we are so familiar in our grates. It is just the same with the decomposition of organic matter. Meat in winter, though very unstable, does not decompose, because there is not a sufficient amount of molecular motion to bring its atoms into close connection with those in the atmosphere for which they have affinities; while in summer it rapidly decomposes, because solar energy overcomes its weak affinities, and thus brings it within the sphere of new ones. And so again, in every chemical reaction we know that a certain amount of heat is required before any compound, however unstable, will yield up its existing combination and form a new one. In short, in every case of relatively stable potential energy, there must always be an integration of new energy from without, in the kinetic form, before the contained energy can be liberated. All the energy possessed not only by living organisms, but also by the water and air of our earth (either in the form of "latent heat" or of chemical separation), is now seen to be due to solar radiations. When we say that the atmosphere is a mechanical mixture, and not a chemical compound, we mean that the atoms composing it are still in their separate energetic state when they combine, they yield up most of their energy, and the force of chemical affinity lock them together.* And this will explain the interesting fact, shown by Professor Tyndall in a series of beautiful experiments, that while the heat-absorbing capacity of the elementary gases, oxygen, hydrogen, and nitrogen, is nil, or very nearly so, that of their com I say most, not all, because of course they retain a small amount at any temperature above the absolute zero. + "Contributions to Molecular Physics in the Domain of Radiant Heat," Memoir II., § 5, seq. pounds is very great. Oxygen and nitrogen, mechanically united as atmospheric air, show no absorption of radiant heat; whereas the same atoms, chemically combined as nitrous oxide, absorb it as 355 to 1; while ammonia absorbs as 1195 to 1. These facts, translated into terms of energy, I conceive to mean that the elementary gases in their state of separation, having already a high specific energy, are incapable of integrating the radiant heat from other bodies; whereas the compounds, having given off energy in the act of combination, are in a position to receive it from other sources. We have consequently no reason to doubt that when the solar energy has all been radiated into space, and none any longer reaches the earth (supposing that epoch to arrive before the earth's orbital motion has brought it into the sun), not only will organic life cease, and water assume the solid form, but the atmosphere, too, will yield up its energy, and be precipitated as a solid mass, under the influence of the absolute zero of temperature,—that is, the total absence of energy. And here I would point out that all these transformations suggest a single general conception which has been hitherto overlooked. It has been usual to speak of kinetic energy as if it were the normal form, and of potential as if it were a peculiar modification; in short, energy has been identified with motion rather than with separation. We shall see, however, if we look more deeply into the question, that kinetic energy is only the transitional stage by which energy is transformed from one of its states, molar, molecular, atomic, or electrical, into another; and, viewed still more comprehensively, it may be regarded as an incident in the transference of energy from ponderable matter to the ætherial medium. In the original diffused state of matter, it possessed universal potential energy of every sort that is, actual separation of masses, molecules, atoms, and electrical factors: in the final aggregated state, matter will possess no energy of any sort, but will have handed it all over to the æther. Kinetic energy (motion) will have been the vehicle by which, through rádiation and ætherial friction, potential energy (separation) will have been handed over from the one to the other. Finally, I shall examine two passages from a couple of our greatest scientific writers, in order to show that confusion of thought has actually resulted from the neglect of the conception of energy as essentially disjunctive, which is advocated in this paper. I choose them purposely from the very deepest thinkers, not in any spirit of carping criticism, but as slight slips which I may have the good fortune to correct. And I choose the second of the two, because it leads up to the final question of all, an answer to which may be fairly expected here, -To what end is all this kosmical process tending? Is the universe bound on the road towards an all-pervading and eternal stagnation, or towards a new birth of countless evolutions, to be repeated through endless cycles of infinite time? Professor Tyndall says, "I have seen the wild stone-avalanches of the Alps, which smoke and thunder down the declivities, with a vehemence almost sufficient to stun the observer. I have also seen snow-flakes descending so softly as not to hurt the fragile spangles of which they were composed; yet to produce, from aqueous vapour, a quantity, which a child could carry, of that tender material, demands an exertion of energy competent to gather up the shattered blocks of the largest stone-avalanche I have ever seen, and pitch them to twice the height from which they fell."* Now, any one who reads over this passage carefully, will see that it expresses the exact opposite of the real fact. The aqueous vapour in its uncondensed state did indeed possess the amount of energy which Professor Tyndall mentions, but this energy was not exerted in the formation of the snow; on the contrary, it was liberated and turned loose upon space. To raise the snow to aqueous vapour again, would require a fresh integration of the same enormous amount of energy: it is in the production of the vapour, there fore, not of the snow, that energy is exerted. Force turns vapour into water, and then into ice, when energy is liberated: energy turns the ice back again into water and vapour. The second passage which I shall examine, is from that profound and encyclopædic philosopher who has been the first in the history of our race to attempt the vast task of systematizing the whole circle of existences, mental and physical, past, present, and future,-I mean Mr. Herbert Spencer. It is this passage which suggests the question above alluded to,-What is to be the final fate of the material universe? Kant, the predecessor of Laplace in the nebular hypothesis, finds in each system of worlds, (I quote for brevity's sake the admirable résumé of Professor Huxley†), “indications that the attractive force of the central mass will eventually destroy its organization, by concentrating upon itself the matter of the whole system; but, as the result of this concentration, he argues for the development of an amount of heat which will dissipate the mass once more into a molecular chaos such as that in which it began." Mr. Herbert Spencer has worked out this idea with his usual thoroughness and perspicuity in his chapter on Dissolution. I can only find room for a short part of his argument, and must refer the reader for details to Mr. Spencer's own pages. After quoting Helmholtz's calculation § of the heat-equivalent for the energy of actual motion and visible position possessed by the earth relatively to the sun, he says, "from ethereal resistance is inferred a retardation of all moving bodies in the solar system,-a retardation which certain astronomers contend, even now shows its effects in the relative nearness to one another of the older planets. If, then, retardation is going on, there must come a time, no matter how remote, when the slowly diminishing orbit of the earth will end in the sun; and though the quantity of molar motion to be then transformed into molecular motion will not be so great as that which the calculation of Helmholtz supposes, it will be great enough to reduce the substance of the earth to a gaseous state."|| Now it is plain that the orbit of the earth can only diminish just in proportion as the centrifugal energy which it possesses is given off to the retarding æther; the retardation being in fact the converse side of the transference of energy. For each unit of energy transferred, the earth will approach a proportionate unit of space nearer the sun. By the time, then, that all the earth's energy has been dissipated, except the |