THE COPLEY MEDALIST OF 1871. 431 



A numerical solution of the relation between heat 

 and work was what Mayer aimed at, and towards the 

 end of his first paper he makes the attempt. It was 

 known that a definite amount of air, in rising one de- 

 gree in temperature, can take up two different amounts 

 of heat. If its volume be kept constant, it takes up 

 one amount; if its pressure be kept constant it takes 

 up a different amount. These two amounts are called 

 the specific heat under constant volume and under 

 constant pressure. The ratio of the first to the second 

 is as 1 : 1.421. No man, to my knowledge, prior to 

 Dr. Mayer, penetrated the significance of these two 

 numbers. He first saw that the excess 0.421 was not, 

 as then universally supposed, heat actually lodged in 

 the gas, but heat which had been actually consumed 

 by the gas in expanding against pressure. The amount 

 of work here performed was accurately known, the 

 amount of heat consumed was also accurately known, 

 and from these data Mayer determined the mechanical 

 equivalent of heat. Even in this first paper he is able 

 to direct attention to the enormous discrepancy be- 

 tween the theoretic power of the fuel consumed in 

 steam-engines, and their useful effect. 



Though this paper contains but the germ of his 

 further labours, I think it may be safely assumed that, 

 as regards the mechanical theory of heat, this obscure 

 Heilbronn physician, in the year 1842, was in advance 

 of all the scientific men of the time. 



Having, by the publication of this paper, secured 

 himself against what he calls ' Eventualitaten/ he de- 

 voted every hour of his spare time to his studies, and in 

 1845 published a memoir which far transcends his first 

 one in weight and fulness, and, indeed, marks an epoch 

 in the history of science. The title of Mayer's first 

 paper was, * Remarks on the Forces of Inorganic Na- 



