When taken together, the two opposite processes thus formulated constitutethe history of every sensible existence under its simplest form. Loss ofinternal motion and consequent integration, eventually followed by gain ofinternal motion and consequent disintegration -- see here a statement comprehensiveof the entire series of changes passed through: comprehensive in an extremelygeneral way, as any statement which holds of sensible existences at largemust be; but still, comprehensive in the sense that all the changes gonethrough fall within it. This will probably be thought too sweeping an assertion,but we shall quickly find it justified. §95. For here we have to note the further all-important fact, thatevery change suffered by every sensible existence, is a change in one orother of these two opposite directions. Apparently an aggregate which haspassed out of some originally discrete state into a concrete state, thereafterremains for an indefinite period without undergoing further integration,and without beginning to disintegrate. But this is untrue. All things aregrowing or decaying, accumulating matter or wearing away, integrating ordisintegrating. All things are varying in their temperatures, contractingor expanding, integrating or disintegrating. Both the quantity of mattercontained in an aggregate and the quantity of motion contained in it, increaseor decrease; and increase or decrease of either is an advance towards greaterdiffusion or greater concentration. Continued losses or gains of substance,however slow, imply ultimate disappearance or indefinite enlargement; andlosses or gains of insensible motion will, if continued, produce completeintegration or complete disintegration. Heat rays falling on a cold mass,augmenting the molecular motions throughout it, and causing it to occupymore space, are beginning a process which if carried far will disintegratethe mass into liquid, and if carried farther will disintegrate the liquidinto gas. Conversely, the decrease of bulk which a volume of gas undergoesas it parts with some of its molecular motion, is a decrease which, if theloss of molecular motion proceeds, will be followed by liquefaction and eventuallyby solidification. And since there is no such thing as a constant temperature,the necessary inference is that every aggregate is at every moment progressingtowards either greater concentration or greater diffusion. §96. A general idea of these universal actions under their simplestaspects having been obtained, we may now consider them under certain morecomplex aspects. Thus far we have supposed one or other of the two oppositeprocesses to go on alone -- we have supposed an aggregate to be either losingmotion and integrating or gaining motion and disintegrating. But though everychange furthers one or other of these processes, neither process is everunqualified by the other. For each aggregate is at all times both gainingmotion and losing motion.
Every mass from a grain of sand to a planet, radiates heat to other masses,and absorbs heat radiated by other masses; and in so far as it does the oneit becomes integrated, while in so far as it does the other it becomes disintegrated.
In inorganic objects this double process ordinarily works but unobtrusiveeffects. Only in a few cases, among which that of a cloud is the most familiar,does the conflict produce rapid and marked transformations. One of thesefloating bodies of vapour expands and dissipates, if the amount of molecularmotion it receives from the Sun and Earth exceeds that which it loses byradiation into space and towards adjacent surfaces; while, contrariwise,if, drifting over cold mountain-tops, it radiates to them much more heatthan it receives, the loss of molecular motion is followed by increasingintegration of the vapour, ending in the aggregation of it into liquid andthe fall of rain. Here, as elsewhere, the integration or the disintegrationis a differential result.
