Joule. 337 



The specific heat may therefore be determined in the 

 following simple manner : — 



' The velocity of the particles of hydrogen, at the tem- 

 perature of 60°, has been stated to be 6,225 ^^^t per second, 

 a velocity equivalent to a fall from the perpendicular 

 height of 602,342 feet. The velocity at 61° will be 6,225 

 ^ |-|^ = 6,230*93 feet per second, which is equivalent to 

 a fall of 603,502 feet. The difference between the above 

 falls is 1,160 feet, which is therefore the space through 

 which I lb. of pressure must operate upon each pound of 

 hydrogen in order to elevate its temperature one degree. 

 But our mechanical equivalent of heat shows that 770 

 feet is the altitude representing the force required to raise 

 the temperature of water one degree ; consequently the 

 specific heat of hydrogen will be y^-^^ = 1*506, calling 

 that of water unity. 



* The specific heats of other gases will be easily deduced 

 from that of hydrogen ; for the whole vis viva and capacity 

 of equal bulks of the various gases will be equal to one 

 another, and the velocity of the particles will be inversely 

 as the square root of the specific gravity. Hence the 

 specific heat will be inversely proportional to the specific 

 gravity, a law which has been arrived at experimentally 

 by De la Rive and Marcet. 



' In the following table I have placed the specific heats 

 of various gases, determined in the above manner, in juxta- 

 position with the experimental results of Delaroche and 

 Berard reduced to constant volume : — 



Experimental Theoretical 



specific heat. specific heat. 



Hydrogen 2-352 i "506 



Oxygen 0'i68 0-094 



Nitrogen 0-195 0-107 



Carbonic oxide . . . .0-158 0-068 



