336 THE POPULAR SCIENCE MONTHLY. 



energy had previously been recognized, or involved in the dispute as 

 to the intimate constitution of heat, may be inferred from what has 

 been already given of the history of heat theory. But in 1822, M. A. 

 Seguin, in a letter to Sir J. F. W. Herschel, 1 explicitly asserted it in 

 support of the dynamical existence of heat, and in explanation of the 

 work obtained from caloric in the steam-engine. The view of the 

 subject he claimed to have derived, some years before, from his uncle, 

 the celebrated Montgolfier. 



Soon after he restated these considerations in a letter to Sir David 

 Brewster, 2 wherein, by a perfectly legitimate course of reasoning, and 

 in a very lucid manner, he showed that the accepted teachings of the 

 calorists led to a violation of this principle of the conservation of 

 energy. For, quoting his own language: 



" If we suppose, indeed, that at each stroke of the piston of a high-pressure 

 steam-engine the quantity of caloric employed is represented exactly by the 

 elevation of temperature of the water of condensation, abstracting all loss, it 

 follows that we have lost nothing in obtaining a very great effect, and that, if it 

 were possible (which is supposable) 3 to condense the caloric contained in a mass 



M 



M into another represented by , in such a manner that it may be reduced into 



x 



vapor at the primitive pressure, we may, by means of a small quantity of caloric, 



produce an indefinite number of oscillations." 



He expressly stated, therefore, that after a mechanical effect had 

 been produced through any given thermal agency, as in a steam- 

 engine, only that quantity of molecular motion or heat which had not 

 been thus appropriated would remain as heat. 



To him, therefore, most undeniably belongs the credit of having 

 first publicly urged the principle of the conservation of energy against 

 the materiality of heat, and of having considered in this connec- 

 tion the reverse phenomenon of the performance of work by thermal 

 agencies. 



The only indefinite or erroneous particular in his statement was 

 that arising from the rather incautious introduction of molecular hy- 

 pothesis. His leading argument was thoroughly scientific, but the 

 oversight or neglect to refer explicitly to the disturbing effect which 

 latent as distinguished from sensible heat might exert upon the ex- 

 perimental verification of his principles, served afterward as a point 

 of attack upon the accuracy of his reasoning in general, and an op- 

 portunity, abundantly improved, to detract from his true merit as an 

 early supporter of the mechanical theory of heat. 



This criticism depends upon and applies with still greater justice 



1 Published in the Edinburgh Philosophical Journal, x., p. 280. 



2 Published in the Edinburgh Journal of Science, iii., p. 276, 1825. 



3 A particular instance of this supposition will be seen in our account of Carnot's 

 engine. 



