M. V. Regnault on the Expansion of Gases. 145 



further apart. But in neither case is the difference in tempera- 

 ture inverted, as would be the case if there were a considerable 

 disengagement of heat produced by the friction of the air against 

 the sides. 



I shall not speak here of experiments I have made on the 

 passage of air through porous plates ; in order to make them in- 

 telligible, it would be necessary to describe apparatus, give nu- 

 merical results, and enter into details inconsistent with the limited 

 extent of this extract. 



Dynamical Expansion. — Second Part. 



In the first part of this memoir I endeavoured to determine 

 the calorific effects produced by a gas which readies a calorime- 

 trical apparatus under a great pressure, which there expands to 

 the external atmospherical pressure, and emerges with the tem- 

 perature of this calorimeter. Thus the gas subjected to the ex- 

 periment only traverses the calorimeter, in the conditions I have 

 mentioned, and no part of the gas remains there. The calorific 

 effect is mainly produced by variations of the vis viva. 



In the second part the gas subjected to experiment is origi- 

 nally contained in the calorimeter in a state of rest, or arrives 

 successively in the calorimeter under the influence of an excess of 

 pressure, to remain there at rest until the end of the experiment. 

 We thus work alternately by compression and expansion. 



In this mode of working, the statical expansion plays the prin- 

 cipal part in the effect produced; but the dynamical expansion 

 intervenes, in conditions resembling those realized in the experi- 

 ments of the first part of this memoir. Clement and Desormes's 

 method, with the modifications it has recently undergone on the 

 part of several experimenters, comes within the same category. 

 The essential difference in my mode of working consists in the 

 fact that the quantities of heat are determined by the calorime- 

 tric method, while my predecessors sought the differences in 

 temperature. 



These researches occupy the greater part of my memoir ; I 

 have repeated them several times, altering the arrangement of 

 the apparatus, which here exerts a very great influence. It is im- 

 possible for me to give an idea by a short extract and without 

 the aid of figures. 



Statical Expansion. 



In the third part of my memoir I have endeavoured to realize 

 experimentally the conditions of the statical expansion of gases, 

 measuring simply the changes of temperature produced. I am 

 again obliged to refer to my complete memoir, which will soon 

 appear ; for the mere statement of my method would involve 

 lengthy explanations. 



Phil. Mag, S. 4. Vol. 39. No. 259. Feb. 1870. L 



