148 ANNUAL OF SCIENTIFIC DISCOVERT. 



volume. The first definition alone coincides with that admitted for 

 solid and liquid bodies, and it is also the only one which has been 

 found practicable for a direct experimental determination. As to the 

 second it seems accessible only to very indirect methods, of so difficult 

 practice that an illustrious natural philosopher, the conscientious Du- 

 long, died laboring at it. 



Among all the researches made to determine the specific heat of 

 gases, under constant pression, that of Delaroche and Berard, which 

 was crowned in 1823 by the Academy, is still the most complete trea- 

 tise on this subject ; it is also that which the nearest approaches the 

 results M. Regriault has just obtained. Delaroche and Berard have 

 obtained to express the specific heat of simple gases, considered under 

 the same volume, numbers which diifer little each from the other. 

 Besides, in augmenting by condensation the density of the atmospheric 

 air, these two natural philosophers have remarked an increase of spe- 

 cific heat ; but they thought they remarked the latter increased less 

 rapidly than the former. Lastly, Delaroche and Berard admitted, ac- 

 cording to theoretical considerations, founded besides upon the direct 

 experiments of Gay-Lussac, that the specific heat of gases rapidly aug- 

 mented with the temperature. Thus, at the same time that oxygen, 

 hydrogen and azote had, under the same volume, the same specific 

 heat, science had admitted as an inextricable complication of the me- 

 chanism of simple gases, that the specific heat of the same mass varied 

 with the temperature and the density. In examining the new figures, 

 obtained by M. Regnault, the student will find that invariability which 

 aids the memory and satisfies the mind. We see that a gramme of air 

 requires, say to elevate its temperature to 10 degrees, the same quan- 

 tity of heat, whatever may be the space it occupies, whatever may be 

 its initial heat. The physical atoms heat themselves each for itself, as if 

 it were alone, and independently of the distance its neighbors may be. 

 And yet, it may be said, when that air is dilated, cold is produced by 

 its forcing outwards the sides which confine it in a vessel. This is an 

 additional reason to regard this lost heat as a purely mechanical phe- 

 nomenon an additional reason to endeavor to find it merely in the 

 labor produced. Let us renounce, then, this false idea that the gases 

 possess so much the more heat as they occupy a larger space. The 

 experiment of connected reservoirs demonstrates the contrary ; it was 

 an inexact notion, founded upon a gross assimilation of a gaseous mass 

 to a sort of sponge, capable of absorbing or expressing the caloric fluid, 

 according to the extension it was allowed to occupy. 



SPECIFIC HEAT OF ELASTIC FLUIDS. 



THE following is an abstract of a paper recently read before the 

 French Academy, on the specific heat of elastic fluids, by M. Regnault. 



After a preliminary introduction and allusion to Ericsson's engines, 

 he says : For more than twelve years I have been occupied in col- 

 lecting the data necessary for the solution of the following problem: 

 What is, theoretically, the motive power which may be obtained from a 



