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 authority, especially in the literature of science, in addressing the Chemical 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 priority 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 perceived 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 afterward suggested to him the important principle with which his name will be connected for ever. . . . We also find in the same memoir (1842) a first determination of the mechanical equivalent of heat deduced from the properties of gases, which is perfectly exact in principle."
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 "Mayer's later papers are extremely remarkable and excessively interesting, and certainly deserve high credit." Yet his claim as the first to determine the mechanical equivalent of heat is still pointedly denied. Indeed, Professor Tyndall himself does not lay the highest stress upon this achievement of Dr. Mayer. He observes: "I must here say distinctly 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, Colding, and Joule.