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The Law of Evolution (continued) §116. Changes great in their amounts and various in their kinds,which accompany those dealt with in the last chapter, have thus far beenignored; or, if tacitly recognized, have not been avowedly recognized. Integrationof each whole has been described as taking place simultaneously with integrationof each of the parts into which it divides itself. But how comes the wholeto divide itself into parts? This is a transformation more remarkable thanthe passage of the whole from an incoherent to a coherent state; and a formulawhich says nothing about it omits more than half the phenomena to be formulated.

This larger half of the phenomena we have now to treat. Here we are concernedwith those. secondary re-distributions of matter and motion which go on alongwith the primary re-distribution. We saw that while in very incoherent aggregates,secondary redistributions produce but evanescent results, in aggregates thatreach and maintain a certain medium state, neither very incoherent nor verycoherent, results of a relatively persistent kind are produced -- structuralmodifications. And our next inquiry must be -- What is the universal expressionfor these structural modifications?

Already an implied answer has been given by the title -- Compound Evolution.

Already in distinguishing as simple Evolution, that integration of matterand dissipation of motion which is unaccompanied by secondary re-distributions,it has been tacitly asserted that where secondary re-distributions occurcomplexity arises; the mass, instead of remaining uniform, must have becomemultiform. The proposition is an identical one. To say that along with theprimary re-distribution there go secondary re-distributions, is to say thatalong with the change from a diffused to a concentrated state, there goesa change from a homogeneous state to a heterogeneous state. The componentso f the mass while becoming integrated have also become differentiated.*

This, then, is the second aspect under which we have to study Evolution.

In the last chapter we contemplated existences of all orders as displayingprogressive integration. In this chapter we have to contemplate them as displayingprogressive differentiation. §117. A growing variety of structure throughout our Sidereal System,is implied by the contrasts which indicate aggregation throughout it. Wehave nebulae that are diffused and irregular, and others that are spiral,annular, spherical. We have groups of stars the members of which are scattered,and groups concentrated in all degrees down to closely-packed globular clusters.

We have these groups differing in the numbers of their members, from thosecontaining several thousand stars to those containing but two. Among individualstars there are great contrasts, real as well as apparent, of size; and fromtheir unlike colours, as well as from their unlike spectra, many contrastsamong their physical states are inferable. Beyond which heterogeneities indetail there are general heterogeneities. Nebulae are numerous in some regionsof the heavens, while in others there are only stars. Here the celestialspaces are almost void of objects, and there we see dense aggregations, nebularand stellar together.

The matter of our Solar System during its integration has become moremultiform. The concentrating gaseous spheroid, dissipating its containedmolecular motion, acquiring more marked unlikeness of density and temperaturebetween interior and exterior, and leaving behind from time to time annularportions of its mass, underwent differentiations which increased in numberand degree, until there was evolved the existing organized group of Sun,planets, and satellites. The heterogeneity of this is variously displayed.

There are the immense contrasts between the Sun and the planets, in bulkand in weight; as well as the subordinate contrasts of like kind betweenone planet and another, and between the planets and their satellites. Thereis the further contrast between the Sun and the planets in respect of temperature;and there are indications that the planets differ from one another in theirproper heats, as well as in the heats which they receive from the sun. Bearingin mind that they also differ in the inclinations of their orbits, the inclinationsof their axes, in their specific gravities, and in their physical constitutions,we see how decided is the complexity wrought in the Solar System by thosesecondary redistributions which have accompanied the primary redistribution. §118. Passing from illustrations, which, as assuming the nebularhypothesis, must be classed as more or less hypothetical, let us descendto evidence less open to objection.

It is now agreed among geologists that the Earth was once a molten mass.