380 FRAGMENTS OF SCIENCE. 



The fight of a pair of pugilists, the motion of an 

 army, or the lifting of his own body by an Alpine 

 climber up a mountain slope, are all cases of mechani- 

 cal energy drawn from the sun. A man weighing 1 50 

 pounds has 64 pounds of muscle ; but these, when dried, 

 reduce themselves to 15 pounds. Doing an ordinary 

 day's work, for eighty days, this mass of muscle would 

 be wholly oxidised. Special organs which do more work 

 would be more quickly consumed : the heart, for ex- 

 ample, if entirely unsustained, would be oxidised in 

 about a week. Take the amount of heat due to the 

 direct oxidation of a given weight of food ; less heat 

 is developed by the oxidation of the same amount of 

 food in the working animal frame, and the missing 

 quantity is the equivalent of the mechanical work ac- 

 complished by the muscles. 



I might extend these considerations ; the work, 

 indeed, is done to my hand but I am warned that 

 you have been already kept too long. To whom then 

 are we indebted for the most striking generalisations 

 of this evening's discourse ? They are the work of 

 a man of whom you have scarcely ever heard 

 the published labours of a Grerman doctor, named 

 Mayer. Without external stimulus, and pursuing his 

 profession as town physician in Heilbronn, this man 

 was the first to raise the conception of the interaction 

 of heat and other natural forces to clearness 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 equivalent of heat from data which only 

 a man of the rarest penetration could turn to account. 



