as applied to Gases and Vapours. 525 



The coefficient — varies in many instances to a great extent 



for the same substance in the solid, liquid, and gaseous states. 

 So far as experiment has as yet shown, it appears not to vary, 

 or not sensibly to vary, with the temperature ; and this I con- 

 sider probable a priori, except at or near the points of fusion of 

 solid substances. 



Apparent specific heat differs from real in consequence of the 

 consumption and production of certain quantities of heat by 

 change of volume and of molecular arrangement, which accom- 

 pany changes of temperature. 



This subject belongs to the theory of the mechanical action of 

 heat. 



Section IV. Of the Coefficients of Elasticity and Dilatation of 



Gases. 



(20.) If in equation (ll)we substitute for ^-7 H-i its value 7^ — , 



we obtain the following value for the elasticity of a gas, 



in which -^ denotes the ratio of the actual weight of unity of 



volume to the weight of unity of volume under unity of pressure, 

 at the absolute temperature C, in the theoretical state of perfect 

 gas; 



T is the absolute temperature ; 



--r(D, 6) is a function of the temperature and density, repre- 

 senting the effect of the attraction of the atomic nucleus or centre 

 in diminishing the superficial elasticity of its atmosphere ; 



and /(D) is a function of the density only, representing the 

 effect of the mutual attractions and repulsions of the atoms upon 

 the whole elasticity of the body. 



From this equation are now to be determined, so far as the 

 experiments of M. Regnault furnish the requisite data, the laws 

 of the deviation of gases from that theoretical state in which the 

 elasticity is proportional to the density multiplied by the abso- 

 lute temperature. 



(21.) The value of — F(D, 6) is given by the infinite series of 

 equations (10), (lOA), substituting in which for its value 



T 



p — T, we obtain the following result : 



Aj, Ag, A3, &c. being a series of functions, the value of which is 

 given by the following equation : 



Phil. Mag. S. 4. No. 14. Suppl. Vol. 2. 2 N 



