290 



Pq = one atmosphere = 2116"-i lb. per square foot. 

 Vq = 8-15725 cubic feet. 

 PqVq = 17,264 foot-pounds. 

 a = 1*9 for the Centigrade scale. 



Specific Heats of One Pound of Carbonic Acid Gas, at the atmos- 

 pheric pressure, in units of work per Centigrade degree. 

 At constant pressure, 300-7 foot-pounds. 

 At constant volume, 235-9 „ ,, 



Eeal specific heat, 235-0 foot-pounds. 



In article 67, the constants, as determined by Messrs Joule and 

 Thomson, of a formula of the same class for atmospheric air, but 

 involving a more complicated function of the reciprocal of the tem- 

 perature, are adapted to the position of the absolute zero adopted in 

 this paper, as follows ; — 



P^Vq = 26,248 in latitude 45°. 

 26,238 in Britain. 

 a^ = 00012811 



I n-n n\ for tho Centigrade scale. 



a.2 = ooo-yj ° 



The Seventh Sectiox of the paper follows, being on the Ther- 

 mic Properties of Vapours. 



Article 68 relates to a principle, the first idea of which was im- 

 perfectly suggested by Carnot, and more fully developed by M. 

 Clausius. By the aid of improved knowledge of the laws of the 

 mechanical action of heat, it is now stated as follows : — 



The latent heat of evaporation, in units of mechanical work, of 

 so much of a substance as fills, in the state of vapour, unity of 

 space more than it fills in the liquid state, is the differential co- 

 efficient of the pressure with respect to the hyperbolic logarithm of 

 the absolute temperature. 



In article 69 the new form of the thermodynamic function, given 

 in article 65 a, is employed to determine the precise law of variation, 

 with the boiling-point, of the total heat of evaporation from a fixed 

 temperature ; a law of which the approximate form, applicable to a 

 substance whose vapour is a perfect gas, and very bulky as compared 



