32t> FRAGMENTS OF SCIENCti. 



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 



