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discourse ? They are the work of a man ol whom you 

 have scarcely ever heard the published labors of a Ger- 

 man doctor, named Mayer* Without external stimulus, 

 and pursuing his profession as town physician in Heil- 

 bronn, this man was the first to raise the conception of 

 the interaction of heat and other natural forces to clear- 

 ness 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 equiva- 

 lent 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 me- 

 chanical 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 Thom- 

 son 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 silence, animated 

 solely by a love of his subject, and arriving at the most 

 important results in advance of those whose lives were 

 entirely devoted to Natural Philosophy. It was the acci- 

 dent of bleeding a feverish patient at Java in 1840 that 



