432 FP.A-MZNTS OF SCIENCE. 



of las 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 he kept constant, it takes up one amount: 

 if its pressure he kept constant it takes up a different 

 amount. These two amounts are called the specific 

 heat under constant volume and under constant pres- 

 sure. The ratio of the first to the second is as 1 : 1*421. 

 No man, to my knowledge, prior to Dr. Mayer, pene- 

 trated 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, hut 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 deter- 

 mined the mechanical equivalent of heat. Even in this 

 first paper he is able to direct attention to the enormous 

 discrepancy between the theoretic power of the rod 

 consumed in steam-engines, and their useful effect. 



Though this paper contains hut 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 c 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 Nature.' 

 The title of his second great essay was, * Organic Motion 

 in its Connection with Nutrition.' In it he expands and 

 the physical principles laid down in his first 



