Equilibration §170. towards what do these changes tend? Will they go on for ever? or will there be an end to them? Can things increase in heterogeneity throughall future time? or must there be a degree which the differentiation andintegration of Matter and Motion cannot pass? Is it possible for this universalmetamorphosis to proceed in the same general course indefinitely? or doesit work towards some ultimate state admitting no further modification oflike kind? The last of these alternative conclusions is that to which weare inevitably driven. Whether we watch concrete processes, or whether weconsider the question in the abstract, we are alike taught that Evolutionhas an impassable limit.
The re-distributions of matter which go on around us, are ever being broughtto conclusions by the dissipation of the motions which effect them. The rollingstone parts with portions of its momentum to the things it strikes, and finallycomes to rest; as do also, in like manner, the various things it has struck.
Descending from the clouds and trickling over the Earth's surface till itgathers into brooks and rivers, water, still running towards a lower level,is at last arrested by the resistance of other water that has reached thelowest level. In the lake or sea thus formed, every agitation raised by awind or the immersion of a solid body, propagates itself around in waveswhich diminish as they widen, and gradually become lost to observation inmotions communicated to the atmosphere and the matter on the shores. Theimpulse given by a player to a harp-string is transformed through its vibrationsinto aerial pulses; and these, spreading on all sides, and weakening as theyspread, soon cease to be perceptible, and are gradually expended in generatingthermal undulations that radiate into space: each aerial pulse causing compressionand evolution of heat. Equally in the cinder which falls out of the fire,and in the vast mass of molten lava ejected by a volcano, we see that themolecular agitation disperses itself by radiation; so that the temperatureinevitably sinks at last to the same degree as that of surrounding bodies.
The proximate rationale of the process exhibited under these several forms,lies in the fact dwelt on when treating of the Multiplication of Effects,that motions are ever being decomposed into divergent motions, and theseinto re-divergent motions. The rolling stone sends off the stones it hitsin directions differing more or less from its own, and they do the like withthe things they hit. Move water or air, and the movement is quickly resolvedinto dispersed movements. The heat produced by pressure in a given directiondiffuses itself by undulations in all directions. That is to say, these motionsundergo division and subdivision, and by continuance of this process withoutlimit they are, though never lost, gradually dissipated.
In all cases, then, there is a progress toward equilibrium. That universalco-existence of antagonist forces which, as we before saw, necessitates theuniversality of rhythm, and which, as we before saw, necessitates the decompositionof every force into divergent forces, at the same time necessitates the ultimateestablishment of a balance. Every motion, being motion under resistance,is continually suffering deductions; and these unceasing deductions finallyresult in the cessation of the motion.
The general truth thus frustrated under its simplest aspect, we must nowlook at under those more complex aspects it usually presents throughout Nature.
In nearly all cases, the motion of an aggregate is compound; and the equilibrationof each of its components, being carried on independently, does not affectthe rest. The ship's bell that has ceased to vibrate, still continues thosevertical and lateral oscillations caused by the ocean-swell. The water ofa smooth stream on whose surface have died away the undulations caused bya rising fish, moves as fast as before towards the sea. The arrested bullettravels with undiminished speed round the Earth's axis. And were the rotationof the Earth destroyed, there would not be implied any diminution of theEarth's movement with respect to the Sun and other external bodies. So thatin every case, what we regard as equilibration is a disappearance of someone or more of the many movements a body possesses, while its other movementscontinue as before. That this process may be duly realized and the stateof things towards which it tends fully understood, it will be well here tocite a case in which we may watch this successive equilibration of combinedmovements more completely than we can do in those above instanced. Our endwill best be served not by the most imposing but by the most familiar example.
