To Mr. Spencer the one conception which spans the universe and solves the widest range of its problems--which reaches outward through boundless space and back through illimitable time, resolving the deepest questions of life, mind, society, history, and civilization, which predicts the glorious possibilities of the future, and reveals the august method by which the Divine Power works evermore,--this one, all-elucidating conception, is expressed by the term EVOLUTION. To this great subject he has devoted his remarkable powers of thought for many years, and stands toward it not only in the relation of an expositor, but also in that of a discoverer. The fact that all living beings are developed from a minute structureless germ has long been known, while the law which governs their evolution--that the change is ever from the homogeneous to the heterogeneous--has been arrived at within a generation. But this fact of growth is by no means limited to the physical history of plants and animals--it is exemplified upon a far more extended scale. Astronomers hold that the solar system has gone through such a process, and Geologists teach that the earth has had its career of evolution. Animals have a mental as well as a physical development, and there is also a progress of knowledge, of religion, of the arts and sciences, of institutions, manners, governments, and civilization itself. Mr. Spencer has the honour of having first established the universality of the principle by which all these changes are governed. The law of evolution, which has been hitherto limited to plants and animals, he demonstrates to be the law of _all_ evolution. This doctrine is unfolded in the first Essay of the present volume, and is more or less fully illustrated in the others; but it will be found elaborately worked out in the second part of _First Principles_. The course of the discussion in this part of the work will be best shown by enumerating the titles to the chapters, which are as follows: I. Laws in General; II. The Law of Evolution; III. The Same continued; IV. The Causes of Evolution; V. Space, Time, Matter, Motion, and Force; VI. The Indestructibility of Matter; VII. The Continuity of Motion; VIII. The Persistence of Force; IX. The Correlation and Equivalence of Forces; X. The Direction of Motion; XI. The Rhythm of Motion; XII. The Conditions Essential to Evolution; XIII. The Instability of the Homogeneous; XIV. The Multiplication of Effects; XV. Differentiation and Integration; XVI. Equilibration; XVII. Summary and Conclusion. A most interesting and fruitful field of thought, it will be seen, is here traversed by our author, and the latest and highest questions of science are discussed under novel aspects and in new relations. Not only do the pages abound with acute suggestions and fresh views, but the entire argument, in its leading demonstrations, and the full breadth of its philosophic scope, is stamped with a high originality.