The Law of Evolution §107. Deduction has now to be verified by induction. Thus far theargument has been that all sensible existences must, in some way or otherand at some time or other, reach their concrete shapes through processesof concentration; and the facts named have been named merely to clarify theperception of this necessity. But we have not arrived at that unified knowledgeconstituting Philosophy, until we have seen how existences of all ordersdo exhibit a progressive integration of Matter and accompanying loss of Motion.
Tracing, so far as we may by observation and inference, the objects dealtwith by the Astronomer and the Geologist, as well as those which Biology,Psychology, and Sociology treat of, we have to consider what direct proofthere is that the Cosmos, in general and in detail, conforms to this law.
Throughout the classes of facts successively contemplated, attention willbe directed not so much to the truth that every aggregate has undergone,or is undergoing, integration, as to the further truth that in every moreor less separate part of every aggregate, integration has been, or is, inprogress. Instead of ****** wholes and wholes of which the complexity hasbeen ignored, we have now to deal with wholes as they actually exist -- mostlymade up of many members combined in many ways. And in them we shall haveto trace the transformation under several forms -- a passage of the totalmass from a more diffused to a more consolidated state; a concurrent similarpassage in every portion of it that comes to have a distinguishable individuality;and a simultaneous increase of combination among such individualized portions. §108. Our Sidereal System by its general form, by its clusters ofstars of various degrees of closeness, and by its nebulae in all stages ofcondensation, gives grounds for suspecting that, generally and locally, concentrationis going on. Assume that its matter has been, and still is being, drawn togetherby gravitation, and we have an explanation of its leading traits of structure-- from its solidified masses up to its collections of attenuated flocculibarely discernible by the most powerful telescopes, from its double starsup to such complex aggregates as the nubeculae. Without dwelling on thisevidence, however, let us pass to the case of the Solar System.
The belief, so variously supported, that this has had a nebular genesis,is the belief that it has arisen by the integration of matter and concomitantloss of motion. Evolution, under its primary aspect, is illustrated mostsimply and clearly by this passage of the Solar System from a diffused incoherentstate to a consolidated coherent state. While, according to the nebular hypothesis,there has been going on a gradual concentration of the Solar System as anaggregate, there has been a simultaneous concentration of each partially-independentmember. The changes of every planet in passing through its stages of nebulousring, gaseous spheroid, liquid spheroid, and spheroid externally solidified,have in essentials -- dissipation of motion and aggregation of matter --paralleled the changes gone through by the general mass; and those of everysatellite have done the like. Moreover, at the same time that the matterof the whole, as well as the matter of each partially-independent part, hasbeen thus integrating, there has been the further integration implied byincreasing combination among the parts. The satellites of each planet arelinked with their primary into a balanced cluster, while the planets andtheir satellites form with the Sun, a compound group of which the membersare more strongly bound together than were the far-spread portions of thenebulous medium out of which they arose.
Even apart from the nebular hypothesis, the Solar System furnishes factshaving a like general meaning. Not to make much of the meteoric matter perpetuallyadded to the Earth, and probably to the other planets, as well as, in largerquantities, to the Sun, it will suffice to name two generally-admitted instances.
The one is the retardation of comets by the ethereal medium, and the inferredretardation of planets -- a process which must in time, as Lord Kelvin argues,bring comets, and eventually planets, into the Sun. The other is the Sun'sstill-continued loss of motion in the shape of radiated heat; accompanyingthe still-continued integration of his mass. §109. To astronomic evolution we pass without break to the evolutionwhich, for convenience, we separate as geologic. The history of the Earth,as traced out from the structure of its crust, carries us back to that moltenstate which the nebular hypothesis implies; and, as before pointed out (§69),the changes called igneous are accompaniments of the advancing consolidationof the Earth's substance and loss of its contained motion. The general effectsand the local effects must be briefly exemplified.
Leaving behind the time when the more volatile elements now existing assolids were kept by the high temperature in a gaseous form, we may beginwith the fact that until the Earth's surface had cooled far below red heat,the mass of water at present covering three-fifths of it, must have existedas vapour. This enormous volume of unintegrated liquid became integratedas fast as dissipation of the Earth's contained motion allowed; leaving,at length, a comparatively small portion uncondensed, which would condensebut for the unceasing absorption of molecular motion from the Sun. In theformation of the Earth's crust we have a similar change similarly caused.
The passage from a thin solid film, everywhere fissured and movable on thesubjacent molten matter, to a crust so thick and strong as to be but nowand then very slightly dislocated by disturbing forces, illustrates the process.
