258 THE FORCES OF INORGANIC NATURE. 



the ground in order that its falling force may be equivalent to 

 the raising of the temperature of an equal weight of water 

 from to 1 C. The attempt to show that such an equa- 

 tion is the expression of a physical truth may be regarded as 

 the substance of the foregoing remarks. 



By applying the principles that have been set forth to the 

 relations subsisting between the temperature and the volume 

 of gases, we find that the sinking of a mercury column by 

 which a gas is compressed is equivalent to the quantity of 

 heat set free by the compression ; and hence it follows, the 

 ratio between the capacity for heat of air under constant pres- 

 sure and its capacity under constant volume being taken as 

 = 1*421, that the warming of a given weight of water from 

 to 1 C. corresponds to the fall of an equal weight from 

 the height of about 365 metres.* If we compare with this 

 result the working of our best steam-engines, we see how 

 small a part only of the heat applied under the boiler is really 

 transformed into motion or the raising of weights ; and. this 

 may serve as justification for the attempts at the profitable 

 production of motion by some other method than the expendi- 

 ture of the chemical difference between carbon and oxygen 

 more particularly by the transformation into motion of elec- 

 tricity obtained by chemical means. 



* When the corrected specific heat of air is introduced into .the calcu- 

 lation this number is increased, and agrees then with the experimental de- 

 terminations of Mr. Joule. 



