4 oo THE POPULAR SCIENCE MONTHLY. 



trating his point by a weight resting upon the earth, suspended at a height -above 

 the earth, and actually falling to the earth. He next fixes his attention on cases 

 where motion is apparently destroyed, without producing other motion ; on the 

 shock of inelastic bodies, for example. Under what form does the vanished 

 motion maintain itself? "Experiment alone," says Mayer, "can help us here." 

 He warms water by stirring it ; he refers 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 sagacity, "may be compared to distilling appara- 

 tus : 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 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 - 421 was not, as then universally sup- 

 posed, heat actually lodged in the gas, but heat which had been actually con- 

 sumed 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 enormous dis- 

 crepancy 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 himself against what he 

 calls " Eventualitiiten," 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 Nu- 

 trition." In it he expands and illustrates the physical principles laid down in 

 his first brief paper. He goes fully through the calculation of the mechanical 

 equivalent of heat. He calculates the performances of steam-engines, and finds 

 that 100 pounds of coal, in a good working engine, produce only the same amount 

 of heat as 95 pounds in an unworking one ; the 5 missing pounds having been 

 converted into work. He determines the useful effect of gunpowder, and finds 

 nine per cent, of the force of the consumed charcoal invested on the moving ball. 

 He records observations on the heat generated in water agitated by the pulping- 

 engine of a paper manufactory, and calculates the equivalent of that heat in 

 horse-power. He compares chemical combination with mechanical combination 

 the union of atoms with the union of falling bodies with the earth. He cal- 

 culates the velocity with which a body starting at an infinite distance would 



* Translations of this and other important papers of Mayer are contained in the vol- 

 ume on the "Correlation of Forces," published by D. Appleton & Co., New York. 



