JULIUS ROBERT MAYER. 405 



correctly perceived and rightly enunciated the general law of nature 

 which we are here considering was a German physician, J. R. Mayer, of 

 Heilbronn, in the year 1842." Again, M. Verdet, an eminent French au- 

 thority, especially in the literature of science, in addressing the Chemi- 

 cal Society of Paris on the mechanical theory of heat in 1862, remarked: 

 " I now come to the researches which, from 1842 to 1849, definitely 

 founded the science. These researches are the exclusive work of three 

 men * who, without concert and without knowing each other, arrived 

 simultaneously in almost the same manner at the same ideas. The pri- 

 ority in the order of publication belongs, without any doubt, to the 

 German physician, Jules Robert Mayer, whose name has occurred so 

 often in these lectures ; and it is interesting to know that it was by 

 reflecting on certain observations in his medical practice that he per- 

 ceived the necessity of an equivalence between work and heat. . . . 

 He perceived in the act of respiration the origin of the motive power 

 of animals ; and the comparison of animals with thermic engines after- 

 ward suggested to him the important principle with which his name 

 will be connected for ever. . . . "VVe also find in the same memoir 

 (1842) a first determination of the mechanical equivalent of heat de- 

 duced from the properties of gases, which is perfectly exact in prin- 

 ciple." 



How Dr. Mayer arrived at the mechanical equivalent of heat, has 

 been briefly referred to by Tyndall in a previous quotation. It will not 

 be possible here to go into the full detail of Mayer's method, but the 

 reader who is curious about it may consult Tyndall's " Heat as a Mode 

 of Motion " for a clear statement, and, for a still completer account, 

 vol. xxviii. of the " Philosophical Magazine," Fourth Series, page 25. 

 Before they had become familiar with Dr. Mayer's work, Professors 

 Thomson and Tait had no word for him but that cf disparagement ; 

 but, as his results were forced upon their attention, they were compelled 

 to concede something to him, and so Tait admits, in 1863, that "May- 

 er's later papers are extremely remarkable and excessively interesting, 

 and certainly deserve high credit." Yet his claim as the first to deter- 

 mine the mechanical equivalent of heat is still pointedly denied. In- 

 deed, Professor Tyndall himself does not lay the highest stress upon 

 this achievement of Dr. Mayer. He observes : "I must here say dis- 

 tinctly that I would not for an instant allow my estimate of Mayer to 

 depend upon his determination of the mechanical equivalent of heat. 

 It is the insight which he had obtained in advance of all other men 

 regarding the relationship of the general energies of the universe, as 

 illustrated in the whole of his writings, that gives him his claim to my 

 esteem and admiration." 



Now, undoubtedly the whole is greater than a part, and Mayer's 

 fame has a far broader foundation than any one special result could 

 afford. But we think that his determination of the mechanical equiv- 



* Mayer, Cokling, and Joule. 



