specific Heat of Elastic Fluids. 481 



present day upon the specific heat of gases, and which are gene- 

 rally recognised by physicists. The limits within which I am 

 compelled to restrict myself in this abstract render it impossible 

 to enter upon any discussion of the methods which have been 

 adopted by my predecessors, or any description of those which 

 I have followed myself. It will be sufficient to remark, that I 

 have encountered in this class of investigations very great diffi- 

 culties, not only in regard to the actual experiments, but like- 

 wise in a theoretical point of view. The remarks which have 

 been made at the commencement of this abstract will render this 

 easily conceivable. Thus, although my first experiments were 

 made five years ago, and announced at that time in my memoirs 

 upon the specific heat of solid and liquid substances, it is only 

 now, after having employed the most difiierent methods, and 

 having caused the elements of correction to destroy each other, 

 that I can with confidence lay the results of my investigation 

 before the Academy. 



According to my experiments, the specific heat of air in rela- 

 tion to that of water is — 



Between - 30° and + \(f 02377 

 Between + 10° and 100° 0-2379 

 Between +100° and 225° 0*2376 



Thus, contrary to the experiments of Gay-Lussac, the specific 

 heat of air does not vary sensibly at difierent temperatures. Ex- 

 periments made with several other permanent gases have led to 

 a similar result. 



In experimenting with atmospheric air under a pressure 

 varying from 1 to 10 atmospheres, I have not found that there 

 is any sensible difference between the quantities of heat disen- 

 gaged by a given mass of air in cooling a certain number of 

 degrees. Thus, contrary to the experiments of Delaroche and 

 Berard, who have shown that there is a very considerable dif- 

 ference for pressures varying only as much as from 1 atmosphere 

 to 1*3 atmosphere, the specific heat of a given mass of gas would 

 be independent of its density. Experiments made with a num- 

 ber of other gases have led to analogous results. Nevertheless 

 I state this law with some degree of reserve ; for I am as yet 

 unable to decide whether the capacity for heat is absolutely con- 

 stant under different pressures, or whether it is subject to a 

 slight correction arising from the state of motion of the gas. 



The specific heat, 0*237, of air in relation to water is con- 

 siderably less than the number 0*2669, adopted by Delaroche 

 and Berard j it is moreover the result of a hundred determina- 

 tions made under various conditions. 



The other elastic fluids, for which I have determined the spe-^ 

 cific heat, are — 



