to all things, whether evolving or not, is a deeper principle, and is, in fact, the primary process in Evolution, while the increase of heterogeneity is the secondary process. At the same time, this new view of the matter made it obvious that Dissolution is everywhere the correlative of Evolution, and that, before the generalization is complete, Dissolution must be recognized as universally tending to undo what Evolution does.
In a new edition of "First Principles," this idea was embodied, and the work recast in conformity with it. The doctrine of Evolution thus attained a higher development. The fundamental antagonism between Evolution and Dissolution comes into the foreground as the cardinal conception. It is shown that every aggregate, simple or compound, is, from the beginning to the end of its existence, subject to these opposing processes of change; that, according as its quantity of contained motion is becoming greater or less, it is tending to integrate or disintegrate—evolve or dissolve; that from moment to moment throughout its whole existence it is simultaneously exposed to both these processes, and that the average transformation it is undergoing expresses the predominance of the one process over the other. This being the universal law to which all material things at all times are subject, there come to be recognized certain derivative laws that are not universal, although highly general. Evolution is distinguished into simple and compound: simple Evolution being that in which the character of the matter and the rate of its integration are such that this primary process of change from a diffused state to a concentrated state is uncomplicated by secondary changes—compound Evolution being that in which, along with the general integrations, there go on more or less marked differentiations and local integrations. Thus the changes which were originally conceived to constitute Evolution itself came to be recognized as in order of time and importance subordinate; integration may go on without differentiation, as in crystals; but differentiation is made possible only by antecedent integration.
The doctrine of Evolution as a theory of the genesis and dissolution of things in the onward course of Nature was elaborately presented in "First Principles," and might have been there left to take its place and its chance among philosophical theories. But it had not been exploited by Mr. Spencer in the way of mental gymnastics, as a piece of novel and ingenious speculation. He believed it to embody a living and applicable principle of the greatest moment. If the law of Evolution be true, it is a truth of transcendent import, no less in the sphere of practical life than in the world of thought, and it was important that it should be carried out in the various fields of its application. Moreover, Mr. Spencer had been drawn to the investigation by his interest in the study of human affairs, and his task was but fairly begun with the establishment of the principle by which they are to be interpreted. In the strict logical order the next step would have been