THE COPLEY MEDALIST OF 1871 453 



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 "An- 

 nalen" a brief preliminary notice of the work then accom- 

 plished. 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 poten- 

 tial 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 re- 

 fers 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 de> 

 stroyed. "Our locomotives," he observes with extraor- 

 dinary sagacity, "may be compared to distilling apparatus: 

 the heat beneath the boiler passes into the motion of the 



