t started by his observation in Java.
But the conviction once formed, that an unalterable relation subsists
between work and heat, it was: inevitable that Mayer should seek to
express it numerically. It was also inevitable that a mind like his,
having raised itself to clearness on this important point, should push
forward to consider the relationship of natural forces generally. At
the beginning of 1842 his work had made considerable progress; but he
had become physician to the town of Heilbronn, and the duties of his
profession limited the time which he could devote to purely scientific
enquiry. He thought it wise, therefore, to secure himself against
accident, and in the spring of 1842 wrote to Liebig, asking him to
publish in his 'Annalen' a brief preliminary notice of the work then
accomplished. Liebig did so, and Dr. Mayer's first paper is contained
in the May number of the 'Annalen' for 1842.

Mayer had reached his conclusions by reflecting on the complex
processes of the living body; but his first step in public was to
state definitely the physical principles on which his physiological
deductions were to rest. He begins, therefore, with the forces of
inorganic nature. He finds in the universe two systems of causes
which are not mutually convertible;--the different kinds of matter and
the different forms of force. The first quality of both he affirms to
be indestructibility. A force cannot become nothing, nor can it arise
from nothing. Forces are convertible but not destructible. In the
terminology of his time, he then gives clear expression to the ideas
of potential and dynamic energy, illustrating 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 quantity generated is the
equivalent of the motion destroyed. 'Our locomotives,' he observes
with extraordinary sagacity, 'may be 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.