326 FRAGMENTS OF SCIENCE. 
oxidation of the same amount of material would sometimes 
yield a less, sometimes a greater, quantity of heat. 
" Hence," says Mayer, " that a fixed relation subsists be- 
tween heat and work, is a postulate of the physiological 
theory of combustion." 
This is the simple and natural account, given subse- 
quently by Mayer himself, of the course of thought 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 ex- 
press 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 inquiry. 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 ac- 
complished. 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 be- 
gins, 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 con- 
vertible 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 
