44 THE HUMAN MOTOR 



But Coriolis contented himself with writing in 1829 : "It 

 would seem that the maximum work of a steam engine depends 

 on the temperature at which the steam is formed f 1 )." 



Thus the principle of Carnot, only awakened rare echoes at that 

 period. 



On the other hand, Mohr,( 2 ) Seguin Senior ( 3 ) affirmed the 

 " equivalence " of the work produced and of the heat which was 

 its origin. And their affirmations were like the reflections of the 

 " dream " this was the word cherished by Hans Oerstedt of 

 the universality of the transformations of the forces of nature. ( 4 ) 



The doctrine of the Equivalence of work and of heat and of 

 all the terrestial energy, was definitely confirmed by Robert 

 Mayer ( 5 ) in 1842, and further developed as to " the energies of 

 life " in 1845. 



33. Principle of Mayer or of Equivalence. Heat is transformed 

 into work, and work into heat, at an absolutely invariable rate, 

 or in other words : A constant relation of equivalence exists 

 between work and heat. 



The quantity of heat necessary to raise 1 kilogramme of water 

 from to 1 centigrade is called a "Grande Calorie" or kilo 

 calorie (C). 



The experiments of Joule, of Hirn, of Edlund, and many other 

 physicists, have proved that : an amount of work of 4264 kgm., 

 or, approximately 425 kilogrammetres, is equal to one "great 



calorie " (C). Inversely a kilogrammetre is equal to T-oi a great 



calorie. 425 kilogrammetres thus defines the mechanical equi- 

 valent of Heat ( 6 ). 



^* _ 425 = E. 

 Heat 



E is the mechanical equivalent of heat. In 1843 the English 

 physicist Joule proved that the work accomplished by an electric 

 motor had its source in the chemical reactions between the acids 

 and the metal of the battery supplying energy to drive it, that is 

 to say, in the oxidation of the zinc. He claimed that the chemical 



(!) Coriolis, TraitS de la M&canique des Corps Solides et du Calcul de I'effet 

 des Machines, 2nd ed., 1844, p. 282 (1st ed., 1829). 



(*) Mohr, Liebig's Ann., vol. XXIV, (1837). 



{*) Seguin senior, Compt's Rendit* Acad. Sc., 1839, vol. XXV. (p. 420). 



( 4 ) Oerstedt, La Dynamologie (Ansicht der Chemischen Naturgesetze], 

 Berlin, 1812. 



( 6 ) Jules-Robert Mayer was born at Heilbronn in 1814 ; son of a chemist, 

 he became a doctor of medicine and travelled to Munich, Paris, etc. His 

 first memoire, of a few pages only, appeared in Annalen der Pharm. und 

 Chemie, of Liebig, vol. XLII ; 1842. 



() So named by Robert Mayer himself. 



