"While the genesis of the Solar System, and of countless other systems like it, is thus rendered comprehensible, the ultimate mystery continues as great as ever. The problem of existence is not solved: it is simply removed further back. The Nebular Hypothesis throws no light on the origin of diffused matter; and diffused matter as much needs accounting for as concrete matter. The genesis of an atom is not easier to conceive than the genesis of a planet. Nay, indeed, so far from making the universe a less mystery than before, it makes it a greater mystery. Creation by manufacture is a much lower thing than creation by evolution. A man can put together a machine; but he cannot make a machine develop itself. The ingenious artisan, able as some have been so far to imitate vitality as to produce a mechanical pianoforte player, may in some sort conceive how, by greater skill, a complete man might be artificially produced; but he is unable to conceive how such a complex organism gradually arises out of a minute structureless germ. That our harmonious universe once existed potentially as formless diffuse matter, and has slowly grown into its present organized state, is a far more astonishing fact than would have been its formation after the artificial method vulgarly supposed. Those who hold it legitimate to argue from phenomena to noumena, may rightly contend that the Nebular Hypothesis implies a First Cause as much transcending 'the mechanical God of Paley' as does the fetish of the savage." This quotation is from an essay on the Nebular Hypothesis, which appeared in the Westminster Review of July, 1858, and which must, therefore, have been written before the eventful date of the reading of Darwin and Wallace's memorable paper before the Linnæan Society. The author of that essay is Mr. Herbert Spencer, and the foregoing extract from it may fitly preface a brief account of his life-work in co-ordinating the manifold branches of knowledge into a synthetic whole. In erecting a complete theory of Evolution on a purely scientific basis "his profound and vigorous writings," to quote Huxley, "embody the spirit of Descartes in the knowledge of our own day." Laying the foundation of his massive structure in early manhood, Mr. Spencer has had the rare satisfaction of placing the topmost stone on the building which his brain devised and his hand upreared. While the sheets of this little book are being passed for press, there arrives the third volume of the Principles of Sociology, which completes Mr. Spencer's Synthetic Philosophy. In the preface to this, the venerable author says: