462 POPULAR LECTURES AND ADDRESSES. 



an axiom in the following terms : " It is im- 

 possible, by means of inanimate material agency, 

 to derive mechanical effect from any portion of 

 matter by cooling it below the temperature of the 

 coldest of the surrounding objects. If this axiom 

 be denied for all temperatures, it would have to 

 be admitted that a self-acting machine might be 

 set to work and produce mechanical effect by 

 cooling the sea or earth, with no limit but the 

 total loss of heat from the earth and sea, or, in 

 reality, from the whole material world." 



My statement of this axiom was limited to 

 inanimate matter because not enough was known 

 either from the natural history of plants and 

 animals or from experimental investigations in 

 physiology to assert with confidence that in animal 

 or vegetable life there may not be a conversion of 

 heat into mechanical effect not subject to the 

 conditions of Carnot's theory. It seemed to me 

 then, and it still seems to me, most probable that. 

 the animal body docs not act as a thermodynamic 

 engine in converting heat produced by the com- 

 bination of the food with the oxygen of the inhaled 



