In logical order the formulation of “First Principles” should have been followed by the application of them to Inorganic Nature.  This great division of Mr. Spencer’s subject is passed over, however; partly because, even without it, the scheme is too extensive to be carried out in the lifetime of one man; and partly because the interpretation of Organic Nature, after the proposed method, is of more immediate importance.  Before noting how Mr. Spencer applies his fundamental principles to the interpretation of the phenomena of life, it may be well to put before the reader’s eye the “formula of evolution” in the author’s own language:  “Evolution is an integration of matter and concomitant dissipation of motion; during which the matter passes from an indefinite, incoherent homogeneity to a definite, coherent heterogeneity; and during which the retained motion undergoes a parallel transformation.”  This law of evolution is equally applicable to all orders of phenomena,—­“astronomic, geologic, biologic, psychologic, sociologic, etc.,”—­since these are all component parts of one cosmos, though disguised from one another by conventional groupings.  It is obvious that, so long as evolution is merely established by induction, it belongs, not to philosophy, but to science.  To belong to philosophy it must be deduced from the persistence of force.  Mr. Spencer holds that this can be done.  For any finite aggregate, being unequally exposed to surrounding forces, will become more diverse in structure, every differentiated part will become the parent of further differences; at the same time, dissimilar units in the aggregate tend to separate, and those which are similar, to cluster together ("segregation"); and this subdivision and dissipation of forces, so long as there are any forces unbalanced by opposite forces, must end at last in rest; the penultimate stage of this process “in which the extremest multiformity and most complex moving equilibrium are established,” being the highest conceivable state.  The various derivative laws of phenomenal changes are thus deducible from the persistence of force.  It remains to apply them to inorganic, organic, and superorganic existences.  The detailed treatment of inorganic evolution is omitted, as we have said, from Spencer’s plan, and he proceeds to interpret “the phenomena of life, mind, and society in terms of Matter, Motion, and Force.”

IV.

The first volume of the “Principles of Biology” consists of three parts, the first of which sets forth the data of biology, including those general truths of physics and chemistry with which rational biology must start.  The second part is allotted to the inductions of biology, or, in other words, to a statement of the leading generalizations which naturalists, physiologists, and comparative anatomists have established.  The third and final part of the first volume of the “Principles of Biology” deals with the speculation commonly known as “the development hypothesis,” and considers its a priori and a posteriori evidences.