72 LAW OF CONSERVATION REALIZED. 



animal were engaged in turning a piece of machinery, or 

 in ascending a mountain, I apprehend that in proportion to 

 the muscular effort put forth for the purpose a diminution 

 of the heat evolved in the system by a given chemical 

 change would be experienced. 



"I will observe, in conclusion, that the experiments detailed 

 in the present paper do not militate against, though they 

 certainly somewhat modify, the views I have previously 

 entertained respecting the electrical origin of chemical heat. 

 I had before endeavoured to prove that when two atoms 

 combine together, the heat evolved is exactly that which 

 would have been evolved by the electrical current due to 

 the chemical action taking place, and is therefore propor- 

 tional to the intensity of the chemical force causing the 

 atoms to combine. I now venture to state more explicitly 

 that it is not precisely the attraction of affinity, but rather 

 the mechanical force expended by the atoms in falling 

 towards one another which determines the intensity of the 

 current, and, consequently, the quantity of heat evolved, so 

 that we have a simple hypothesis by which we may explain 

 why heat is evolved so freely in the combination of gases, 

 and by which, indeed, we may account ' latent heat ' as a 

 mechanical power prepared for action as a watch spring is 

 when wound up. Suppose, for the sake of illustration, that 

 81b. of oxygen and lib. of hydrogen were presented to one 

 another in the gaseous state and then exploded, the heat 

 evolved would be about I degree Fahr. in 60,000 lbs. of 

 water, indicating a mechanical force expended in the com- 

 bination equal to a weight of about 50,000,000 lbs. raised to 

 the height of 1 foot. Now, if the oxygen and hydrogen 

 could be presented to each other in a liquid state, the heat 

 of combination would be less than before, because the atoms 



