CONVERTIBILITY OF HEAT AND MOTION. 323 



stices between the material atoms, or other hypotheses of like 

 nature, have not availed to solve the problem. It is, notwith- 

 standing, of no less wonderfully simple a nature than the laws 

 of the lever, about which the founder of the peripatetic phi- 

 losophy cudgelled his brains in vain. 



After what has gone before, the reader cannot be in any 

 doubt about what is the course now to be pursued. We must 

 again make quantitative determinations : we must measure 

 and count. 



If we proceed in this direction and measure the quantity 

 of heat developed by mechanical agency, as* well as the 

 amount of force used up in producing it, and compare these 

 quantities with each other, we at once find that they stand to 

 each other in the simplest conceivable relation that is to say, 

 in an invariable direct proportion, and that the proportion also 

 holds when, inversely, mechanical force is again produced by 

 the aid of heat. 



Putting these facts into brief and plain language, we may 

 say, 



Heat and motion are transformable one into the other. 



We cannot and ought not, however, to let this suffice us. 

 We require to know how much mechanical force is needed for 

 the production of a given amount of heat, and conversely. 

 In other words, the law of the invariable quantitative relation 

 between motion and heat must be expressed numerically. 



When we appeal hereupon to experiment, we find that 

 raising the temperature of a given weight of water one degree 

 of the Centigrade scale corresponds to the elevation of an 

 equal weight to the height of about 1,200 [French] feet. 



This number is THE MECHANICAL EQUIVALENT OF HEAT. 



The production of heat by friction and other mechanical 

 operations is a fundamental fact of such constant occurrence, 

 that the importance of its establishment on a scientific basis 

 will be recognized by naturalists without any preliminary 



