166 



presenting successfully the theory of expansive heat, is consistent 

 with that of radiant heat and light, and well adapted to form a basis 

 for that of the elasticity of solids, the author shews, by a method 

 more simple than those foi'merly employed by him, that, according 

 to this hypothesis, the pressure of a perfect gas is represented by 



P = (NQ + /.)1 



N and h being specific coefficients. Let V^ be the volume of unity of 

 weight of a perfect gas at a standard pressure P^, and temperature r^ ; 

 then absolute temperature, as measured by a perfect gas thermome- 

 ter, has this value — 



■^0 -^00 



The absolute temperature of total privation of heat is 



P V 



The quantity of heat in unity of weight of a body is 

 Q = K (r - x) 

 where 



P V 



fe = 



is the coefficient of real specific heat.* 



The introduction of this value of heat in terms of temperature 

 into the equations of the first sub-section, reproduces all the formulae 

 which were deduced directly from the hypothesis in the author's pre- 

 vious researches. In particular, the greatest proportion of heat con- 

 vertible into mechanical power in an expansive engine working be- 

 tween the temperatui-es r^ and Tj, is 



The value of/ (Q) is 



ft N" X I hyp. log r + - I 



In the Fourth Sub-Section, the author investigates the inferences 

 to be di'awn from the experiments of Messrs Joule and Thomson. 



* These conclusions have since been confirmed by M. Regnault's experiments 

 on the Specific Heat of Gases. (See Comptes Rendus, 1853, and Philos. Mag., 

 June 1853.) 



