For among associated men the progress is ever towards a merging of individualactions in the actions of corporate bodies. In militant life this is seenin the advance from the independent fighting of separate warriors to thecombined fighting of regiments, and in industrial life in the advance fromthe activities of separate workers to the combined activities of factoryhands. So is it, too, when instead of acting alone citizens act in bodies-- companies, unions, associations, etc. While, then, during Evolution theescaping motion becomes, by widening dispersion, more disintegrated, themotion that is for a time retained, becomes more integrated; and so, considereddynamically, Evolution is a decrease in the relative movements of parts andan increase in the relative movements of wholes -- using the words partsand wholes in their most general senses. The advance is from the motionsof simple molecules to the motions of compound molecules; from molecularmotions to the motions of masses; and from the motions of smaller massesto the motions of larger masses.
The accompanying change towards greater multiformity among the retainedmotions, takes place under the form of an increased variety of rhythms. Amultiplication of rhythms must accompany a multiplication in the degreesand modes of aggregation, and in the relations of the aggregated masses toincident forces. The degree or mode of aggregation will not, indeed, affectthe rate or extent of rhythm where the incident force increases as the aggregateincreases, which is the case with gravitation: here the only cause of variationin rhythm is difference of relation to the incident force; as we see in apendulum which, though unaffected in its movements by a change in the weightof the bob, alters its rate of oscillation when its length is altered orwhen, otherwise unchanged, it is taken to the equator. But in all cases wherethe incident forces do not vary as the masses, every new order of aggregationinitiates a new order of rhythm: witness the conclusion drawn from the recentresearches into radiant heat and light, that the molecules of different gaseshave different rates of undulation.* Sothat increased multiformity in the arrangement of matter necessarily generatesincreased multiformity of rhythm; both through increased variety in the sizesand forms of aggregates, and through increased variety in their relationsto the forces which move them. That these motions, as they become more integratedand more heterogeneous, must become more definite, is a proposition thatneed not detain us. In proportion as any part of an evolving whole segregatesand consolidates, and in so doing loses the relative mobility of its components,its aggregate motion must obviously acquire distinctness.
Here, then, to complete our conception of Evolution, we must contemplatethroughout the Cosmos, these metamorphoses of retained motion which accompanythe metamorphoses of component matter. We may do this with comparative brevity: the reader having now become so familiar with the mode of looking at thefacts, that less illustration will suffice. To save space, it will be convenientto deal with the several aspects of the metamorphoses at the same time. §140. Masses of diffused matter moving towards a common centre, frommany points at many distances with many degrees of indirectness, must carryinto the nebulous mass eventually formed, numerous momenta unlike in theiramounts and directions. As the integration progresses, such parts of thesemomenta as conflict are mutually neutralized, and dissipated as heat. Unlessthe original distribution is quite symmetrical, which is infinitely improbable,rotation will result. The mass having at first unlike angular velocitiesat the periphery and at various distances from the centre will have its differencesof angular velocity gradually reduced; advancing towards a final state, nownearly reached by the Sun in which the angular velocity of the whole massis the same -- in which the motion is integrated. So, too, with each planetand satellite. Progress from the motion of a nebulous ring, incoherent andadmitting of much relative motion within its mass, to the motion of a densespheroid, is progress to a motion that is completely integrated. The rotation,and the translation through space, severally become one and indivisible.
Meanwhile, there has been established that further integration displayedby the motions of the Solar System as a whole. Locally in each planet andits satellites, and generally in the Sun and the planets, we have a systemof simple and compound rhythms, with periodic and secular variations, formingtogether an integrated set of movements.
Along with advancing integration of the motions there has gone advancein the multiformity and distinctness of them. The matter which, in its originaldiffused state, had movements that were confused, indeterminate, or withoutsharply-marked distinctions, has, during the evolution of the Solar System,acquired definitely heterogeneous movements. The periods of revolution ofall the planets and satellites are unlike; as are also their times of rotation.
Out of these definitely heterogeneous motions of a simple kind, arise othersthat are complex, but still definite; -- as those produced by the revolutionsof satellites compounded with the revolutions of their primaries; as thoseof which precession is the result; and as those which are known as perturbations.
