THE COPLEY MEDALIST OF 1871. 439 



the animal organism can also generate heat outside of 

 itself. A blacksmith, for example, by hammering can 

 heat a nail, and a savage by friction can warm wood to 

 its point of ignition. Now, unless we give up the 

 physiological axiom that the living body cannot create 

 heat out of nothing, ' we are driven/ says Mayer, ' to 

 the conclusion that it is the total heat generated within 

 and without that is to be regarded as the true calorific 

 effect of the matter oxidised in the body.' 



From this, again, he inferred that the heat gener- 

 ated externally must stand in a fixed relation to the 

 work expended in its production. For, supposing the 

 organic processes to remain the same; if it were possi- 

 ble, by the mere alteration of the apparatus, to generate 

 different amounts of heat by the same amount of work, 

 it would follow that the oxidation of the same amount 

 of material would sometimes yield a less, sometimes a 

 greater, quantity of heat. ' Hence/ says Mayer, ' that 

 a fixed relation subsists between heat and work, is a 

 postulate of the physiological theory of combustion.' 



This is the simple and natural account, given sub- 

 sequently by Mayer himself, of the course of thought 

 started by his observation in Java. But the conviction 

 once formed, that an unalterable relation subsists be- 

 tween work and heat, it was inevitable that Mayer 

 should seek to express it numerically. It was also in- 

 evitable that a mind like his, having raised itself to 

 clearness on this important point, should push forward 

 to consider the relationship of natural forces generally. 

 At the beginning of 1842 his work had made consider- 

 able progress; but he had become physician to the 

 town of Heilbronn, and the duties of his profession 

 limited the time which he could devote to purely sci- 

 entific enquiry. He thought it wise, therefore, to se- 

 cure himself against accident, and in the spring of 



