242 



decrease of /i with the temperature should be so clearly brought out 

 by observations performed on different liquids, at different tempera- 

 tures. 



(2.) On the Heat developed hy the Compression of Air. 



Carnot demonstrates the following proposition : — 



Equal volumes of all elastic fluids, when compressed to equal 

 smaller volumes, disengage equal quantities of heat. 



This very remarkable proposition, given as a theorem by Carnot, 

 was enunciated as a probable experimental law by Dulong ; and it 

 therefore affords a very powerful confirmation of Carnot's funda- 

 mental principle. 



Mr Joule of Manchester has made some important experiments 

 on this subject. The view which he takes of a thermal " equiva- 

 lent" for motive power is at variance with Carnot's theory, but his 

 experimental results agree with its indications in a very satisfactory 

 manner. In endeavouring to effect a comparison, I found that the 

 following propositions are a consequence of Carnot's Theory. 



1. In compressing a gas of which the temperature is kept in- 

 variable, the amount of work spent is exactly proportional to the 

 quantity of heat developed. 



2. The amount of work necessary to produce a unit of heat in 

 this manner is the same, whatever be the gas operated on, but de- 

 pends upon the temperature, being determined by the expression 



■ K 



(3.) On the Specific Heats of Gases. 



Carnot proves, as a theorem, that the excess of the specific heat* 

 under a constant pressure above the specific heat at a constant vo- 

 lume is the same for all gases at the same temperature and pressure. 



This result agrees well with the experimental results obtained by 

 Dulong. 



Carnot's theory affords the following determinate expression for 

 the difference alluded to in the enunciation : 



M.a+Etf 



* i. e. The " capacity for heat" of a unit of volume. 



