THK COPLEY MKDALlxT OF 1871. 327 



to the force expended in overcoming friction. Motion in 

 both cases disappears; but heat is generated, and the quan- 

 tity generated is the equivalent of the motion destroyed. 

 " Our locomotives," he observes with extraordinary sagac- 

 ity, "maybe compared to distilling apparatus: the heat 

 beneath the boiler passes into the motion of the train, and 

 is again deposited as heat in the axles and wheels." 



A numerical solution of the relation between heat and 

 work was what Mayer aimed at, and toward the end of his 

 first paper he makes the attempt. It was known that a 

 definite amount of air, in rising one degree 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 vol- 

 urneand 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 num- 

 bers. He first saw that the excess 1.421 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 per- 

 formed 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 enor- 

 mous discrepancy between the theoretic power of the fuel 

 consumed in steam-engines, and their useful effect. 



Though this paper contains but the germ of his further 

 labors, 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 him- 

 self against what he calls " Eventualitaten," he devoted 

 every hour of his spare time to his studies, and in 1845 

 published a memoir which far transcends his first one 

 in weight and fullness, and, indeed, marks an epoch in 

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

 was, " Remarks on the Forces of Inorganic Nature." The 

 title of his second great essay was," Organic Motion in its 

 Connection with Nutrition." In it he expands and illus- 

 trates the physical principles laid down in his first brief 



