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LX VII. On the Caloric of Gases and Vapours, hy M. PoissoN ; 

 f)-om the Annalcs dc CJiimic, ^o??2exxiii. ^?. 3S7 .• 'with Obser- 

 vations hy John Herapath, Esq. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



THINKING M.Poisson's paper, which you had the goodness 

 to put into my hands, would not be unacceptable to your En- 

 glish readers, I have taken the trouble to translate it from the 

 French, and have added some notes and observations which 

 appeai-ed necessary either to elucidate it or to set its merits 

 in a proper light. 



From this paper and those of M. Laplace it is plain with 

 what ardour the subject of gases and heat is pursued on the 

 continent. Would our English philosophers but lend their 

 aid in the securer course of deciding some of the more impor- 

 tant and disputed points by experiments, it is manifest we 

 should speedily come to decisive conclusions respecting the 

 nature and laws of heat. In hopes that some of them will 

 shortly take up the complete experimental investigation of so 

 important a question, 



I am, gentlemen. 



Yours truly, 

 Cranford, October 15, 1823. J, HebapaTH. 



On the Caloric of Gases and Vapours ; hy M. Poisson*. 



§ I. Let p be the density of a gas, 5 its temperature in centi- 

 grade degrees, and p its elastic force, or its pressure on a unity 

 of surface ; then shall we have 



_p=«p(l+«6) _ (1) 

 a. and a being two coefficients of which the first is the same 

 for every gas, and equal to "00375, and the other should be 

 given for each particular gas. The total quantity of caloric 

 contained in a given weight of gas, a grammef for instance, 

 we have no method known of computing ; but we may consi- 

 der the excess of this quantity above that which a gramme of 

 the gas contains under a pressure and temperature arbitrarily 

 chosen. Denoting this excess by q, it will become a function 



* This paper sets out with a formula drawn from the hypothesis, tliat 

 the increments of expansion under a constant pressure are proportional to 

 the increments of heat. Other hypothetical views are afterwards intro- 

 duced to account for particular phenomena, the success of which will best 

 appear in the course of the paper. It may however here be observed, that 

 though this paper does not profess to descend deeply into physical princi- 

 ples, it is nevertheless completely hypothetical ; but I shall not stop to 

 point out all the hypothetical parts ; I shall merely call the attention of the 

 reader to the more material points. — J. H. 



f 15-4457i) English grains Troy. 



of 



