454 FRAGMENTS OF SCIENCE 



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 tempera- 

 ture, 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 con- 

 stant 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 between the theo- 

 retic 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, 



