THti COPLEY MEDALIST OP 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 
d'efinite 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- 
ume 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 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 
