THE CENTURY'S PROGRESS IN PHYSICS 



else even came abreast their line of thought, let alone 

 passing it. 



But then, in 1824, a French philosopher, Sadi Carnot, 

 caught step with the great Englishmen, and took a long 

 leap ahead by explicitly stating his belief that a definite 

 quantity of work could be transformed into a definite 

 quantity of heat, no more, no less. Carnot did not, in- 

 deed, reach the clear view of his predecessors as to the 

 nature of heat, for he still thought it a form of " impon- 

 derable" fluid; but he reasoned none the less clearly as 

 to its mutual convertibility with mechanical work. But 

 important as his conclusions seem now that we look 

 back upon them with clearer vision, they made no im- 

 pression whatever upon his contemporaries. Carnot's 

 work in this line was an isolated phenomenon of histori- 

 cal interest, but it did not enter into the scheme of the 

 completed narrative in any such way as did the work of 

 Kumford and Davy. 



The man who really took up the broken thread where 

 Kumford and Davy had dropped it, and wove it into a 

 completed texture, came upon the scene in 1840. His 

 home was in Manchester, England ; his occupation that 

 of a manufacturer. He was a friend and pupil of the 

 great Dr. Dalton. His name was James Prescott Joule. 

 When posterity has done its final juggling with the 

 names of our century, it is not unlikely that the name of 

 this Manchester philosopher will be a household word 

 like the names of Aristotle, Copernicus, and Newton. 



For Joule's work it was, done in the fifth decade of our 

 century, which demonstrated beyond all cavil that there 

 is a precise and absolute equivalence between mechani- 

 cal work and heat ; that whatever the form of mani- 

 festation of molar motion, it can generate a definite and 



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