THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



♦ 



[FOURTH SERIES.] 



OCTOBER 1872. 



XXIX. On the Cooling of Gases, 

 By MM. Jamin and Richard*. 



DULONG and Petit, in their celebrated work on the laws of 

 cooling, studied first the effect of a vacuum. They found 

 that the velocity of cooling* of a thermometer in the centre is 

 expressed by the formula 



v = ma^{a*—\). 



a is an invariable quantity, m a coefficient proportional to the 

 surface and the emissive power of the thermometer, t-\-6 and 6 

 the temperatures of the thermometer and the enclosure. 



No objection can be made to this law, which has moreover 

 been confirmed by the admirable researches of De la Provostaye 

 and Desains. 



The second part of the work, which is devoted to the study of 

 gases, is not so unexceptionable. Dulong and Petit, remarking 

 that in this case the diminution of temperature is more rapid, 

 assume : — (1) that the radiation persists without alteration, just 

 as if it took place m ?;«cwo ; (2) that the augmentation of the 

 observed effect represents the cooling-power of the gas. They 

 then measure the total velocity of cooling, V, from which they 

 subtract v (that which would take place in vacuo for the same 

 values of 6 and /), and find that the remainder v^ satisfies the 

 relation 



«;'=?iHC/^-233. 



It is sensibly equal to 0*5 ; and ?z is a coefficient which dc- 



* Translated from the Comptes Rendus de rAcadernle des Sciences, 

 vol. Ixxv. pp. 105-113. 



Phil, Mag. S. 4. Vol. 44. No. 293. Oct, 1872. R 



