NATURAL PHILOSOPHY BY WILHELM OSTWALD TRANSLATED BY THOMAS SELTZER _With the author's special revision for the American edition_ NEW YORK HENRY HOLT AND COMPANY 1910 COPYRIGHT, 1910, BY HENRY HOLT AND COMPANY _Published November_, 1910 THE QUINN & BODEN CO. PRESS RAHWAY N. J. The original of this book was published as volume I in Reclam's BÜCHER DER NATURWISSENSCHAFT. PREFACE The beginning of the twentieth century is marked by a sudden rise of interest in philosophy. This is especially manifest in the vast growth of philosophic literature. The present movement, it is noteworthy, is by no means a revival proceeding from the academic philosophy traditionally represented at the universities, but has rather the original character of _natural philosophy_. It owes its origin to the fact that after the specialization of the last half century, the synthetic factors of science are again vigorously asserting themselves. The need finally to consider all the numerous separate sciences from a general point of view and to find the connection between one's own activity and the work of mankind in its totality, must be regarded as the most prolific source of the present philosophic movement, just as it was the source of the natural philosophic endeavors a hundred years ago. But while that old natural philosophy soon ended in a boundless sea of speculation, the present movement gives promise of permanent results, because it is built upon an extremely broad basis of experience. The laws of energy in the inorganic world and the laws of evolution in the organic world furnish mental instruments for a conceptual elaboration of the material provided by science, instruments capable not only of unifying present knowledge, but also of evoking the knowledge of the future. If it is not permissible to regard this unification as exhaustive and sufficient for all time, yet there is still so much left for us to do in working over the material we have on hand from the general points of view just mentioned, that the need for systematizing must be satisfied before we can turn our gaze upon things more remote.