250 Professor Ty^idaVs Lecture on Force. 



oxidised in about a week. Take the amount of beat due to the 

 direct oxidation of a given amount of food ; a less amount of heat 

 is developed by this food in the working animal frame, and the 

 missing quantity is the exact equivalent of the mechanical work 

 which the body accomplishes. 



I might extend these considerations ; the work, indeed, is done 

 to my hand — but I am warned that I have kept you already too 

 long. To whom, then, are we indebted for the striking general- 

 isations of this evening's discourse ? All that I have laid before 

 you is the work of a man of whom you have scarcely ever heard. 

 All that I have brought before you has been taken from the la- 

 bors of a German physician, 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 in- 

 teraction of natural forces to clearness in his own mind. And 

 yet he is scarcely ever heard of in scientific lectures, 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 his first paper on the "Mechanical Value of 

 Heat," in 1843 ; but in 1842 Mayer had actually calculated the 

 mechanical equivalent of heat from data which a man of rare 

 originality alone could turn to account. From the velocity of 

 sound in air Mayer determined the mechanical equivalent of heat. 

 In 1845 he published his Memoir on " Organic Motion," and ap- 

 plied the mechanical theory of heat in the most fearless and pre- 

 cise manner to vital processes. He also embraced the other 

 natural agents in his chain of conservation. In 1853 Mr. Wa- 

 terston proposed, independently, the meteoric theory of the sun's 

 heat, and in 1854, Professor William Thomson applied his ad- 

 mirable mathematical powers to the development of the theory ; 

 but six years previously, the subject had been handled in a mas- 

 terly manner by Mayer, and all that I have said on this subject 

 has been derived from him. When we consider the circum- 

 stances of Mayer's life, and the period at which he wrote, we 

 cannot fail to be struck with astonishment at what he has accom- 

 plished. Here was a man of genius working in silence, animated 

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

 tant results, some time in advance of those whose lives were en- 

 tirely devoted to Natural Philosophy. It was the accident of 

 bleeding a feverish patient at Java in 1840, that led Mayer to 

 speculate on these subjects. He noticed that the venous blood 



