456 POPULAR LECTURES AND ADDRESSES, 



essentially taken in by the engine at the higher 

 temperature and given out at the lower tem- 

 perature. All this was taught by Carnot, in 1824, 

 but with it, in his original essay, was involved the 

 then almost universally prevailing idea that heat 

 was a material substance, and that therefore the 

 quantity of heat given out by the engine at the 

 lower temperature must be exactly equal to the 

 quantity of heat taken in at the higher temperature. 

 Carnot died in 1832 (two years after the Revolu- 

 tion of 1830), at the age of thirty-six. If he had 

 lived a few years longer, or if his short life, begun 

 in the Reign of Terror, had been less troubled l 



1 "These researches " [in thermodynamics] "were roughly 

 interrupted by a great event, the Revolution of July, 1830. . . . 

 Sadi frequented the popular meetings of this epoch, without, hov. 

 going beyond the character of a simple observer. . . . On the day of 

 the funeral of General La Marque, Sadi \vas taking a walk out 

 of curiosity in the neighbourhood of the insurrection. A mounted 

 soldier, who seemed drunk, passed at a gallop through the 

 brandishing his sabre and striking at passers by. Sadi dashed 

 forward, skilfully avoided the weapon of the soldier, sei/ed him by 

 the leg, dragged him off his horse, laid him gently in the gutter, 

 and continued his walk ; stealing himself away from the acclama- 

 tions of the crowd, who were astonished at this bold coup dc niaiiT." 

 --From A if>/ii</i/t', p. 78, by his brother Ilippolyte 



Carnot, referred to below. 



