passed from one method of thought to another by slow processes of intellectual growth which required time as well as exertion, and he has pushed further on in the scientific direction and away from the metaphysical position than perhaps any other writer. How complete has been the revolution in his own mind is well illustrated by a passage in his preface referring to his former work.
He says: "I deem it important to have it understood at the outset, that this treatise is in no sense a further exposition of the doctrines of a book ('The Philosophy of Nature'—Boston: Crosby & Nichols, 1848) which I published more than a third of a century ago. That book was written while I was under the spell of Hegel's ontological reveries—at a time when I was barely of age, and still seriously affected with the metaphysical malady which seems to be one of the unavoidable disorders of intellectual infancy. The labor expended in writing it was not, perhaps, wholly wasted, and there are things in it of which I am not ashamed, even at this day. Cut I sincerely regret its publication, which is in some degree atoned for, I hope, by the contents of the present volume."
Having slowly recovered from his serious Hegelian attack and mastered in a very thorough manner the principles and methods of modern physical science, it was inevitable that Judge Stallo's attention should be forcibly drawn to the relations of these two systems, and to the question how far science is still dominated by the old metaphysical method. It is his opinion that the metaphysical influence lingers and rules in scientific thought to a greater degree than is commonly suspected. It is generally supposed that physical science, at any rate, has quite freed itself from the mischievous tendencies of metaphysical speculation, and that Newton's admonition to the physicists, "to beware of metaphysics," has been so effectually heeded that this branch of investigation may be taken as illustrating the true scientific method in its purity and perfection. The author of the "Concepts and Theories of Modern Physics" holds that this assumption is but partially true, and the present work is devoted to a comprehensive examination of what may be regarded as basal theories of physics, to the evidence that may be given of their errors, and to tracing out the metaphysical origin of these errors. We can not here do better than to restate his position as given by himself in the preface to his book: "It will be seen at once, upon a most cursory glance at any one of the chapters of this little book, that it is in no wise intended as an open or covert advocacy of a return to metaphysical methods and aims; but that, on the contrary, its tendency is throughout to eliminate from science its latent metaphysical elements, to foster and not to repress the spirit of experimental investigation, and to accredit instead of discrediting the great endeavor of scientific research to gain a sure foothold on solid, empirical ground, where the real data of experience may be reduced without ontological prepossessions. An attentive perusal of these pages will make it clear, I think, that this endeavor is continually thwarted by the insidious intrusion into the meditations of the man of science of the old metaphysical spirit. This fact having been established, it was incumbent on me to ascertain, if possible, its causes and, within the narrow limits at my command, to develop its consequences."
The first or introductory chapter of Judge Stallo's book is devoted to a statement of those theoretical ideas which are maintained to be fundamental in physical science. These involve the mechanical conception of the constitution of matter, or the atomomolecular theory. A large number of the most authoritative writers are quoted, who agree that, in the language of Du Bois-Reymond, "the resolution of all changes in the material world into motions of atoms, caused by their constant central forces, would be the completion of natural science." The author sums up the doctrine as follows: "The mechanical theory of the universe undertakes to account for all physical phenomena by describing them as variances in the structure or configuration of material systems. It strives to apprehend all phenomenal diversities in the material world as varieties in the grouping of primordial units of mass, to recognize all phenomenal changes as movements of unchangeable elements, and thus to exhibit all apparent qualitative heterogeneity as mere quantitative difference."