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XV. Note on the History of the Dynamical Theory of Heat. 

 By J. P. Joule, LL.D., F.R.S. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



WILL you permit me to trouble your readers with a few 

 remarks on the subject of my friend Professor TyndalFa 

 lecture at the Royal Institution, reported in your last Number ? 

 In this lecture he enforces the claims of M. Mayer, a philosopher 

 whose merit has perhaps been overlooked by some of our English 

 physicists, and unaccountably so by his fellow-countrymen. I 

 myself was only imperfectly acquainted with his papers when, in 

 good conscience and with the materials at command, I gave a 

 sketch of the history of the dynamical theory of heat, in my paper 

 published in the Philosophical Transactions for 1850. M. Mayer's 

 merit consists in having announced, apparently without knowledge 

 of what had been done before, the true theory of heat. This is no 

 small merit, and I am the last person w r ho would wish to detract 

 from it. But to give to Mayer, or indeed to any single indivi- 

 dual, the undivided praise of propounding the dynamical theory 

 of heat, is manifestly unjust to the numerous contributors to that 

 great step in physical science. Two centuries ago, Locke said 

 that " Heat is a very brisk agitation of the insensible parts of the 

 object, which produces in us that sensation from whence we de- 

 nominate the object hot; so that what in our sensation is heat, 

 in the object is nothing but motion.' 3 In 1798, Rumford, in- 

 quiring into the source of heat developed in the boring of cannon, 

 observed that it was ( ' extremely difficult, if not quite impossible, 

 to form any distinct idea of anything capable of being excited 

 and communicated, in the manner the heat was excited and com- 

 municated in these experiments, except it be motion." In 1812, 

 Davy wrote, " The immediate cause of the phenomena of heat, 

 then, is motion, and the laws of its communication are precisely the 

 same as the laws of the communication of motion"*; and he con- 

 firmed his views by that original and most interesting experiment 

 in which he melted ice by friction. In 1839, Seguin published 

 a work entitled De V Influence des Chemins de Fer. He shows 

 that the theory generally adopted would lead to the absurd con- 

 clusion that a finite quantity of heat can produce an indefinite 

 quantity of mechanical action, and remarks (p. 328), " II me parait 

 plus naturel de supposer qu'une certaine quantite de calorique dis- 

 parait dans Facte meme de la production de la force ou puissance 

 mecanique, et reciproquement." At p. 383 he remarks, " La 

 force mecanique qui apparait pendant Pabaissement de tempera- 

 ture d'un gaz comme de tout autre corps qui se dilate, est la 

 * Elements of Chemical Philosophy, p. 94. 

 Phil Mag. S. 4. Vol. 24. No. 159. Aug. 1862. K 



