Natural history, properly so called, or the study of the origin and past history of the universe, the earth, and its organic population, is much more recent than the history of mankind. Immanuel Kant was the first to lay the foundations of a mechanical cosmogony in his remarkable _Natural History of the Heavens_ (1755), and Laplace gave mathematical shape to his ideas in 1796. Geology, also, or the story of the evolution of the earth, was not founded until the beginning of the eighteenth century, and did not assume a definite shape until the time of Hoff and Lyell (1830). Later still (1866) were laid the foundations of the science of organic evolution, when Darwin provided a sound foundation, in his theory of selection, for the theory of descent which Lamarck had proposed fifty years before. In sharp contrast to this purely empirical method, which is favored by most men of science in our day, we have the purely speculative tendency which is current among our academic philosophers. The great regard which the critical philosophy of Immanuel Kant obtained during the nineteenth century has recently been increased in the various schools of philosophy. As is known, Kant affirmed that only a part of our knowledge is empirical, or _a posteriori_--that is, derived from experience; and that the rest of our knowledge (as, for instance, mathematical axioms) is _a priori_--that is to say, reached by the deductions of pure reason, independently of experience. This error led to the further statement that the foundations of science are metaphysical, and that, though man can attain a certain knowledge of phenomena by the innate forms of space and time, he cannot grasp the "thing in itself" that lies behind them. The purely speculative metaphysics which was built up on Kant's apriorism, and which found its extreme representative in Hegel, came at length to reject the empirical method altogether, and insisted that all knowledge is obtained by pure reason, independently of experience.