ON MATTER AND FORCE. 37 



foot-pound, and the unit of heat that quantity 

 which raises one pound of water one deg. Fahr. ; 

 then the mechanical equivalent of heat is 772 

 foot-pounds. 



The equivalence of other forms of energy has 

 yet to be determined by experiment. 



Meanwhile, according to modern ideas, the 

 different forms are so related to one another, 

 that none can be lost, and none can be produced 

 except by passing into or out of some other 

 form of energy. 



"But," says Mr. Faraday (Researches in 

 Chemistry and Physics, p. 459), "after all, 

 the principle of the conservation of force may 

 by some be denied. Well, then, if it be un- 

 founded, even in its application to the smallest 

 part of the science of force, the proof must be 

 within our reach, for all physical science is so. 

 In that case, discoveries as large, or even larger, 

 than any yet made, may be anticipated. I do 

 not resist the search for them ; for no one can 

 do harm, but only good, who works with an 

 earnest and truthful spirit in such a direction. 

 But let us not admit the destruction or creation 

 of force without clear and constant proof. 



" Just as the chemist owes all the perfection of 



