78 Intelligence and Miscellaneous Articles. 



In these calculations the specific heats are taken between zero and 

 200°, and the coefficients of dilatation are in relation to the interval 

 from zero to 100°; it is probable that between 100° and 200° the 

 coefficients of dilatation of air and hydrogen retain sensibly the 

 same value, and that the coefficient of dilatation of carbonic acid 

 tends to diminish, so that the value calculated for y" is a little too 

 small. 



Conclusion. — If for each of these three gases (hydrogen, air, and 

 carbonic acid) we take the proportion of the heat consumed in in- 

 ternal work to the specific heat under a constant pressure, we find the 



following values for -^, -^, -^ : — 

 C C C 



Hydrogen 0*297 



Air 0-297 + 0-904 



Carbonic acid 0-317 + 0-035 



We see, therefore, that the heat consumed in internal work, when 

 the gas dilates under the constant pressure of the atmosphere be- 

 tween zero and 200°, is a fraction of the specific heat under constant 

 pressure, which goes on increasing from hydrogen to air and from 

 air to carbonic acid. 



We may likewise compare the quantities of heat expended in in- 

 ternal work under the same circumstances by considering the three 

 gases under the same volume at the temperature of melting ice. If 

 we take as the common volume the volume occupied by 1 kilog. of 

 hydrogen, the weight of equal volumes of air and carbonic acid are 

 respectively 



1 kilog. , 1 kilog. 



5- and ^-x 1*529; 



0-06926 0-06926 



and the quantities of heat consumed in internal work are respectively 

 for these three gases, considered under the same volume, 



y A „ 1'529 



•y, — , and v X , 



7 0-06926 Y 0-06926 



or Hydrogen y 



Air ,l-0015y + 0'013 



Carbonic acid l-505y + 0'146. 



These quantities of heat likewise increase from hydrogen to air 

 and from air to carbonic acid. 



The law of Dulong and Petit applied to absolute specific heats, 

 therefore, leads us to arrange hydrogen, air, and carbonic acid, with 

 regard to internal work, in the order which the experiments of 

 Messrs. W. Thomson and Joule assign to these very gases. — 

 — Comptes Rendus, January 1 1, 1869, vol. lxviii. pp. 95-98. 



INVESTIGATIONS ON OBSCURE CALORIFIC SPECTRA. 

 BY M. DESAINS. 



I have the honour to lay before the Academy the results of new 

 investigations on obscure calorific spectra. The questions I have 

 deavoured to solve are the following : — 

 (1) Given, in a spectrum formed by a prism of definite nature and 



