478 Intelligence and Miscellaneous Articles. 



The ninth column of the Table gives the differences between the 

 calculated and observed values. 



M. A. Cornu has obliged us by placing at our service one of the 

 specimens of quartz (No. 6) which had served M. Mascart for the 

 determination of the rotatory power. It has given us results not 

 sensibly differing from those which we had previously obtained*. 

 — Comptes Rendus de VAcademie des Sciences, tome lxxxiii. pp. 

 818-821. 



ON THE RATIO OF THE TWO SPECIFIC HEATS OF A GAS. 

 BY CH. SIMON. 



My purpose, in this communication, is to determine, by the 



theory, the ratio — of the two specific heats of a perfect gas, simple 

 c 



and tetratomic. 



When a gas is regarded as a system of material points the 



C 

 mutual actions of which are negligible, the ratio — is readily found 



to be equal to -| ; and M. Yillarceau has proved that the result is 

 the same when a mutual action is supposed between two gaseous 

 molecules which is a function of their distance and directed along 

 the right line that joins their centres of gravity ; bnt this result 

 has only been verified hitherto in the case of mercury vapour, 

 which is considered to be monatomic. For any gas whatever, M. 

 Villarceaut has given the expression 



2 1 /dZSiptfi cU\ 



~ 3 Ec V dd + S2 W 



where the quantity in the brackets represents the variation, per 

 degree of increase of temperature, of the energy of the system of 

 the atoms in their motions about the centres of gravity of the mole- 

 cules of which they are parts. This quantity consequently includes 

 the internal vibrations and the rotations of the molecules. Igno- 

 rant as we are of the laws which govern the intramolecular forces, 

 it would perhaps be impossible to reach by calculation the internal 

 vibrations ; but it appears easier to take into consideration the rota- 

 tions of the molecules about their centres of gravity ; and it is to be 

 presumed that, if account be taken of the rotations, the internal 



* With this quartz we found, for the value of the rotation of the light 

 of sodium, by Mascart's method, 21°-725 ; and for different lines, by the 

 method of Fizeau and Foucault, we arrived at the following numbers : — 



A. a. D r h. M. O. P. Q. R. 



12-677 14-319 21-750 47-509 58-900 70-538 74-622 78-623 85-017 



t Comptes Rendus, May 22, 1876. 



