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It seems peculiarly appropriate that this volume should be dedicated to you. Knowing the eminent esteem in which you are held in the circles of European science, I cannot doubt that the distinguished authors of the following essays would cordially approve this connection of your name with their introduction to the American public.

There is, besides, a further reason for this in that large coincidence of purpose which is manifest in their labors and your own. For while the pervading design of the present collection is to widen the range of thought by unfolding a broader philosophy of the energies of nature, your own comprehensive course of research-beginning with an extended series of experimental investigations in chemical physics and physiology, and rising to the consideration of that splendid problem, the bearing of science upon the History of the Intellectual Development of Europe-has powerfully contributed to the same noble end; that of elevating the aim and enlarging the scope of scientific inquiry.

I gladly avail myself of this occasion to say how greatly I am indebted to your writings, in which accurate and profound instruction is so often and happily blended with the charms of poetic eloquence. That you may live long to enjoy your well-won honors, and to contribute still further to the triumphant advance of scientific truth, is the heartfelt wish of

Yours truly,

E. L. Y.


In his address before the British Association for the Advancement of Science last year, the President remarked that the new views of the Correlation and Conservation of Forces constitute the most important discovery of the present century. The remark is probably just, prolific as has been this period in grand scientific results. No one can glance through the current scientific publications without perceiving that these views are attracting the profound attention of the most thoughtful minds. The lively controversy that has been carried on for the last two or three years respecting the share that different men of different countries have had in their establishment, still further attests the estimate placed upon them in the scientific world.

But little, however, has been published in this country upon the subject; no complete work, I believe, except the admirable volume of Prof. Tyndall on "Heat as a Mode of Motion," in which the new philosophy is adopted, and applied to the explanation of thermal phenomena in a very clear and forcible manner. I have, therefore, thought it would be a useful service to the public to reissue some of the ablest presentations of these views which have appeared in Europe, in a compact and convenient form. The selection of these discussions has been determined by a desire to combine clearness of exposition with authority of statement. In the first of these respects the essays will speak for themselves; in regard to the last I may remark that all the authors quoted stand high as founders of the new theory of forces. Although I am not

aware that Prof. Liebig has made any claims in this direction, yet it can scarcely be doubted that his original researches in Animal Chemistry tended strongly toward the promotion of the science of vital dynamics.

The work of Professor Grove, which is here reprinted in full, has a high European reputation, having passed to the fourth edition in England, and been translated into several continental languages. It is hardly to the credit of science in our country, that this is the first American edition. The eloquent and interesting paper of Helmholtz, though delivered as a popular lecture, was translated for the Philosophical Magazine, and has been very highly appreciated in scientific circles. The three articles of Mayer, which were also translated for the Philosophical Magazine, will have interest not only because of the great ability with which the subjects are treated, but as emanating from a man who stands perhaps preeminent among the explorers in this new tract of inquiry. The researches of Faraday in this field have been conspicuous and important, and his argument is marked by the depth and clearness which characterize, in an eminent degree, the writings of this extraordinary man. The essay of Liebig forms a chapter in the last edition of his invaluable 'Familiar Letters on Chemistry,' which has not been republished here; and, as it touches the relation of the subject to organic processes, it forms a fit introduction to the final article of the series by Dr. Carpenter, on the "Correlation of the Physical and Vital Forces." The eminent English physiologist has worked out this branch of the subject independently, and the paper quoted gives evidence of being prepared with his usual care and ability. A certain amount of repetition is of course unavoidable in such a collection, yet the reader will find much less of this than he might be inclined to look for, as each writer, in elaborating the subject, has stamped it with his own originality.

In the introduction I have attempted to bring forward certain facts in the history of these discoveries, in which we as Americans have a special interest, and also to indicate several applications of the new principles which are not treated in the volume. It seemed best to confine the general discussion to those aspects of the subject upon which most thought had been expended, and which may be regarded as settled among advanced scientific men. But there are other applications of the doctrine, of the highest interest, which though incomplete are yet certain, and these will be found

briefly noticed in the introductory observations--too briefly, I fear, to be satisfactory. Those, however, who desire to pursue still further this branch of the inquiry-the correlation of the vital, mental, and social forces--are referred to the last edition of Carpenter's "Principles of Human Physiology; " Morell's "Outlines of Mental Philosophy;" Laycock's "Correlations of Consciousness and Organization; " Sir J. K. Shuttleworth's address before the Social Science Congress of 1860, on the "Correlation of the Moral and Physical Forces; " Hinton's "Life in Nature," and "First Principles" of Herbert Spencer's new system of Philosophy. The first and last of these works are the only ones, it is believed, that have appeared in an American form, and the last is much the ablest of all; I was chiefly indebted to it in preparing the latter part of the introduction. The biographical notices, brief and imperfect as they are, it is hoped may enhance the reader's interest in the volume.

I have been specially incited to procure the publication of a work of this kind, by the same motive that has impelled me to write upon the subject elsewhere; a conviction of our educational needs in this direction. The treatment of a vast subject like this in ordinary school text-books, is at best quite too limited for the requirements of the active-minded teacher; to such, a volume like the present may prove invaluable.

But a more serious difficulty is that, until compelled by the demands of intelligent teachers, the compilers of school-books will pass new views entirely by, or give them a mere hasty and careless notice, while continuing to inculcate the old erroneous doctrines. And thus it is that from inveterate habit, or intellectual sluggishness, or a shrewd calculation of the indifference of teachers, outworn and effeto ideas continue to drag through school-books for half a century after they have been exploded in the world of liying science. He who continues to teach the hypothesis of caloric, falsifies the present truth of science as absolutely as he would do in teaching the hypothesis of phlogiston; in fact, the reasons of fered for persisting in the erroneous notions of the materiality of heat-convenience of teaching, unsettledness of the new vocabulary, &c., are precisely those that were offered for clinging to phlogiston, and rejecting the Lavoiserian chemistry of combustion. Both conceptions have no doubt been of service, but both were transitional, and having done their work they become hindrances

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