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Eighth, Thomson's theory of dissipation.

As regards the true theory of the connexion of heat with mechanical effect, this list contains all the most important direct steps, nearly in chronological order; but it is to be remembered that experimental investigation, mainly due to Joule, has indissolubly connected by laws of equivalence all forms of energy, including even such mysterious forms as are observed in electro-chemistry and electro-magnetism; and that a complete account of the dynamical theory of heat necessarily involves, what we propose to give on another occasion, an account of the one grand law of natural philosophy--the CONSERVATION OF ENERGY.

In the brief sketch we have given, a vast amount of valuable matter has been of necessity omitted, but we are not conscious of having left unnoticed any direct step of real consequence to the development of the true theory of heat. Where the results of early experiments were sufficiently accurate, we have not alluded to subsequent more perfect ones; and many curious, but not very important, points have not been mentioned. The details of such a history as this would fill volumes.

The work of M. Verdet consists of two lectures delivered in 1862 to the Chemical Society of Paris, and is evidently intended for an audience already well acquainted with the fundamental principles of natural philosophy. Like all the works of the most distinguished of French scientific men, it is clear and distinct almost to a fault; the author has evidently not only read deeply, but carefully arranged his ideas, before writing his lectures; and the consequence is the production of a little treatise, brief but comprehensive, in which every sentence has its meaning and its definite bearing on the development of the subject. We shall not consider the mathematical developments which are interspersed through the text, and which occur freely in the notes, further than to remark that they show how extensive is the author's acquaintance with all that has been done in the extension of the theory. Nor do we profess at present to review even the popular portion in all its details, because M. Verdet las considered in his lectures, not merely the direct relation between heat and mechanical effect, to which our article has been limited, but has included in his comprehensive sketch the indirect developments of heat from work by the intervention of electrical currents, etc., and has, in fact, treated of the whole theory of energy. To some of his remarks on this subject, we may take exception in our next article; but so far as our present subject is concerned, we consider that M. Verdet has on the whole fairly represented its history, and that he has put it

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before his readers in an extremely clear and impressive form. More could hardly be said of an essay which does not in any way pretend to novelty. Since a critic can hardly be supposed to have done his work properly unless he find some fault, we are tempted to express our opinion that M. Verdet would have done wisely in devoting much less space to the consideration of Hirn's errors as to the actual amount of heat put out of existence in the working of a steam-engine. Not that we object to the introduction of the results, but there appears to be no necessity for such an elaborate refutation of conclusions known to be wrong, especially as M. Verdet tells us that Hirn has renounced his erroneous opinions.

As to the history of the science, we are astonished that M. Verdet should say of Mayer's method of determining the equivalent of heat that it is " parfaitement exacte quant au principe"! We have already shown that this idea is untenable. Besides, we can hardly reconcile this statement of M. Verdet's with the last clause of the following sentence, which occurs in the very next page of his work, with reference to Joule: “C'est à ses expériences de 1845, sur les effets calorifiques de la dilatation et de la compression des gaz qu'il appartenait de donner droit de cité dans la science aux idées nouvelles ; ce sont ses expériences sur le frottement qui ont donné de l'équivalent mécanique de la chaleur la première détermination digne de confiance; ce sont ses vues sur la constitution des gaz qui ont donné le premier, et jusqu'ici le seul exemple d'une explication complète d'un phénomène dont la théorie fait prévoir les lois sans en indiquer le mécanisme." Nothing could be more candid than this, nor could more have possibly been expected, as M. Verdet has evidently overlooked Joule's friction result of 1843, which was unfortunately only mentioned, in few words and without any details, in an appendix to a paper devoted to a totally different class of experiments. In our second article we shall recur to M. Verdet's very interesting lectures.

Dr. Tyndall's volume contains a series of lectures delivered in the Royal Institution in London, which of course are much more popular in form than those of M. Verdet. We wish we could call them as clear and definite. Unfortunately they are deficient in the precise qualities which the French philosopher possesses so completely. Grandiloquence, especially when rising almost to the style of the modern sensational school of fictionwriters, is not adapted even to popular science; true scientific language is ever calm and dignified, and we fear the worst when we hear of magnetic needles moving as if “ inspired by a sudden affection " for the audience, medals “struck dead by the excitement of the magnet," and other catastrophes too numerous to mention. In another sense, also, the language employed is bad; it is ambiguous, and this is utterly indefensible in a scientific work. Examples of such ambiguity can be quoted almost without number, but we shall confine ourselves to one or two of the most important. Thus, the words “force,” “strength,” and “energy," are sometimes used as antagonistic, and anon as synonymous terms. Energy, again, is confounded with “moving force," which has a perfectly definite meaning in no way related to energy. In collisions, we are told, “the heat generated increases as the square of the velocity.” This is a palpable mistake, evidently arising from the confusion in the author's mind of the phrase A varies as B (or is proportional to B) with the very different one, A increases as B (i.e., the rate of change of A is proportional to B). Again, what can be the meaning of such a sentence as this : “Let me now pass from the sun to something less-in fact, to the opposite pole of nature”? Or this: “as we proceed light will gradually appear, and irradiate retrospectively our present gloom”! It is needless to collect further examples of this constant perversion of the common meanings not only of scientific, but even of popular, words.

With the exception of these blemishes, and of other more serious faults which we shall presently consider, the volume, so far as it goes, is creditable enough. Many experimental novelties, well suited to the lecture-room, are carefully described ; and, on the whole, the work is calculated to prove exceedingly interesting even to the scientific reader. But we look in vain through its pages for so much as a mere mention of Carnot; and, beyond a few casual remarks about the disappearance of heat in the production of mechanical effect, there is nothing to give the reader even a hint, that the laws which regulate the production of work from heat are now as well known and as capable of being popularized, as anything in Natural Philosophy. That radiant heat and light are identical, and that there are many peculiarities in their radiation and absorption by matter, which require only patient experiment for their discovery, was known long ago; and though the new results obtained by the author are curious, and in some cases even startling, they can scarcely, even if completely verified by other experimenters, claim anything like the comparative value which has been assigned them in this work, to the exclusion of so much that is of vital importance.

But the dissipation of energy is not even alluded to; and many other remarkable branches of the subject, due as much to the mathematician as to the experimenter, are alike ignored; though, in a volume with such a title as this, they might be expected to

Dr. Tyndall's Lectures.

69

have found a corner. They can be made intelligible to any educated reader, and ought to have a place in every work, especially a British work, in which the subject is treated with any detail.

But what we most object to in Dr. Tyndall's volume is his erroneous history of the development of the subject. His errors in this way are numerous and great. Thus he says, “Dr. Mayer enunciated the exact relation between heat and work, giving the number which is now known as the 'mechanical equivalent of heat.'”—(The italics are our own.) Compare this with the facts as recorded above; first as to the value of Mayer's statements, and second as to the number which Mayer did give. Again, “ Mr. Thomson suggested that the stretched India-rubber might shortenwhen heated. We cannot fancy that any one would consider this a fair representation of a prediction mathematically deduced, without hypothesis, as a result necessarily following from known facts. The beautiful reasoning of J. Thomson, about the lowering of the freezing-point of water by pressure, is introduced in such a manner that any uninstructed reader would fancy Dr. Tyndall had the chief merit, Messrs. Hopkins and Fairbairn a secondary position, and Thomson merely the credit of making a happy guess, in the establishment of this most important result. For the credit of British science, we hope that Dr. Tyndall will, when a second edition of his really interesting work is called for, pay some attention to the by-no-means microscopic faults which it possesses in such rich profusion.

[Note.—Since the above was put in type we have seen in the Philosophical Magazine (Jan. 1864) a brief account of the work of Colding. So far as this enables us to judge, he appears to have been led by a species of metaphysical reasoning to the idea of the conservation of energy; but, unlike other speculators, to have appealed to experiment before publishing his views. The value (350 kilogrammètres) of the equivalent of heat which he thus obtained in 1843 from friction experiments, is not much more accurate than that deduced from Rumford's data, —and is not to be compared with Joule’s of the same year. Still Colding evidently went to work in the right way, and deserves an amount of credit to which Séguin and Mayer have no claim.

ART. III.--1. Mémoires d'un Bibliophile. Par M. TENANT DE

LATOUR. Paris, 1861. 2. The Book-Hunter. By J. HILL BURTON. Second Edition.

Edinburgh, 1863.

NOTHING, we suspect, is less intelligible to the uninitiated than the sort of pleasure which the inveterate book-collector derives from his peculiar pursuit, or than the intense eagerness which he often displays in it. One of the fraternity—a man of vast knowledge, and of great power as a thinker and a writer after having followed the “ business," as he calls it, from early youth to well-nigh fourscore, lately declared that it “ had never palled upon him for a single moment."1 Yet, to most persons, this amassing of literary treasures is simply a “mania ;" even Mr. Burton, who ought to know better, has thought proper, in his very pleasant and witty Book-Hunter, to affect the satirical and depreciatory strain ; and whether he intended it or not, the impression left on the minds of his readers is, that a collector is a poor lost creature who greatly needs to be taken care of by his friends ; an office, by the way, which these same friends (particularly if they happen to belong to the female order), are always very ready to perform. The great Lord Bacon too once threatened Sir Thomas Bodley, whom he found slow to appreciate his new philosophy, with "a Cogitation against Libraries,” to be added to the Cogitata et Visa. And we all remember Sir Walter's quiet quizzing of the book-collecting race in the mock heroics which he puts into the mouth of Mr. Jonathan Oldbuck : " Happy, thrice happy, Snuffy Davie; and blessed were the times when thy industry could be so rewarded!”

But notwithstanding our having such high authorities against us, we are about to venture a word or two in defence of this much misunderstood and much calumniated class. And we shall attempt to show that even what are commonly regarded as the oddest and most fantastic of their proceedings, often possess a foundation of intelligent interest which the very dullest must comprehend as soon as it is pointed out to them. To most persons, for instance, the fastidiousness of a genuine book-lover about the editions which he admits into his library; his frequent preference of an old and dingy copy, to the finest modern re print; and above all, his anxiety to have two or three different editions of the same work in his possession, are quite unaccount

1 Preface to Catalogue of Books, the Property of a Political Economist [J. R. M'Culloch, Esq.), with Critical and Bibliographical Notices. Lond. (privately printed) 1862.

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