e climber up a mountain slope, are
all cases of mechanical energy drawn from the sun. A man weighing 150
pounds has 64 pounds of muscle; but these, when dried, reduce
themselves to 15 pounds. Doing an ordinary day's work, for eighty
days, this mass of muscle would be wholly oxidised. Special organs
which do more work would be more quickly consumed: the heart, for
example, if entirely unsustained, would be oxidised in about a week.
Take the amount of heat due to the direct oxidation of a given weight
of food; less heat is developed by the oxidation of the same amount of
food in the working animal frame, and the missing quantity is the
equivalent of the mechanical work accomplished by the muscles.

I might extend these considerations; the work, indeed, is done to my
hand--but I am warned that you have been already kept too long. To
whom then are we indebted for the most striking generalisations of
this evening's discourse? They are the work of a man of whom you have
scarcely ever heard--the published labours of a German doctor, named
Mayer. Without external stimulus, and pursuing his profession as town
physician in Heilbronn, this man was the first to raise the conception
of the interaction of heat and other natural forces to clearness in
his own mind. And yet he is scarcely ever heard of, and even to
scientific men his merits are but partially known. Led by his own
beautiful researches, and quite independent of Mayer, Mr. Joule
published in 1843 his first paper on the 'Mechanical Value of Heat;'
but in 1842 Mayer had actually calculated the mechanical equivalent of
heat from data which only a man of the rarest penetration could turn
to account.

In 1845 he published his memoir on 'Organic Motion,' and applied the
mechanical theory of heat in the most fearless and precise manner to
vital processes. He also embraced the other natural agents in his
chain of conservation. In 1853 Mr. Waterston proposed, independently,
the meteoric theory of the sun's heat, and in 1854 Professor William
Thomson applied his admirable mathematical powers to the development
of the theory; but six years previously the subject had been handled
in a masterly manner by Mayer, and all that I have said about it has
been derived from him. When we consider the circumstances of Mayer's
life, and the period at which he wrote, we cannot fail to be struck
with astonishment at what he has accomplished. Here was a man of
genius working in silenc