Let us now mark how the process of evolution is furthered by this multiplicationof effects. An incident force decomposed by the reactions of a body intoa group of unlike forces, becomes the cause of a secondary increase of multiformityin the body which decomposes it. By the reactions of the various parts, differentlymodified as we have seen they must be, the incident force itself must bedivided into differently modified parts. Each differentiated division ofthe aggregate thus becomes a centre from which a differentiated divisionof the original force is again diffused. And since unlike forces must produceunlike results, each of these differentiated forces must produce, throughoutthe aggregate, a further series of differentiations. This secondary causeof the change from homogeneity to heterogeneity, obviously becomes more potentin proportion as the heterogeneity increases. When the parts into which anyevolving whole has segregated itself, have diverged widely in nature, theywill necessarily react very diversely on any incident force -- they willdivide an incident force in to so many strongly contrasted groups of forces.
And each of them becoming the centre of a quite distinct set of influences,must add to the number of distinct secondary changes wrought throughout theaggregate. Yet another corollary must be added. The number of unlike partsof which an aggregate consists, is an important factor in the process. Everyadditional specialized division is an additional centre of specialized forces,and must be a further source of complication among the forces at work throughoutthe mass -- a further source of heterogeneity. The multiplication of effectsmust proceed in geometrical progression. §157. The scattered parts of an irregular nebula in course of beingdrawn together or integrated, cannot display in a definite manner the secondarytraits of evolution: these presuppose an aggregate already formed. We cansay only that the half-independent components, each attracted by all andall by each, exhibit in their various momenta, different in their amountsand directions, a multiplication of effects produced by a single gravitativeforce.
But assuming that the integrative process has at length generated a singlemass of nebulous matter, then the simultaneous condensation and rotationshow us how two effects of the aggregative force, at first but slightly divergent,become at last widely differentiated. An increase of oblateness in this spheroidmust take place through the joint action of these two forces, as the bulkdiminishes and the rotation grows more rapid; and this we may set down asa third effect. The genesis of heat, accompanying augmentation of density,is a consequence of yet another order -- a consequence by no means simple;since the various parts of the mass, being variously condensed, must be variouslyheated. Acting throughout a gaseous spheroid, of which the parts are unlikein their temperatures, the forces of aggregation and rotation must work afurther series of changes: they must set up circulating currents, both generaland local. At a later stage light as well as heat will be generated. Thuswithout dwelling on the likelihood of chemical combinations and electricdisturbances, it is manifest that, supposing matter to have originally existedin a diffused state, the once uniform force which caused its aggregation,must have become gradually divided into different forces; and that each furtherstage of complication in the resulting aggregate, must have initiated furthersubdivisions of this force -- a further multiplication of effects, increasingthe previous heterogeneity.
This section of the argument may however be adequately sustained withouthaving recourse to any such hypothetical illustrations as the foregoing.
The astronomical attributes of the Earth will, even by themselves, sufficefor our purpose. Consider first the effects of its rotation. There is theoblateness of its form; there is the alternation of day and night; thereare certain constant marine currents; and there are certain constant aerialcurrents. Consider next the secondary series of consequences due to the divergenceof the Earth's plane of rotation from the plane of its orbit. The many variationsof the seasons, both simultaneous and successive, which pervade its surface,are thus caused. External attraction of the Moon and Sun acting on the equatorialprotuberance of this rotating spheroid with inclined axis, produces the motioncalled nutation, and that slower and larger one from which follows the precessionof the equinoxes, with its several sequences. And then, by this same force,are generated the tides, aqueous and atmospheric.
