A HISTORY OF SCIENCE 



work. But important as his conclusions seem now 

 that we look back upon them with clearer vision, they 

 made no impression whatever upon his contemporaries. 

 Carnot's work in this line was an isolated phenomenon 

 of historical interest, but it did not enter into the 

 scheme of the completed narrative in any such way as 

 did the work of Rumford and Davy. 



The man who really took up the broken thread where 

 Rumford 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 occupa- 

 tion that of a manufacturer. He was a friend and 

 pupil of the great Dr. Dal ton. His name was James 

 Prescott Joule. When posterity has done its final 

 juggling with the names of the nineteenth 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 

 the century, which demonstrated beyond all cavil that 

 there is a precise and absolute equivalence between 

 mechanical work and heat ; that whatever the form of 

 manifestation of molar motion, it can generate a def- 

 inite and measurable amount of heat, and no more. 

 Joule found, for example, that at the sea - level in 

 Manchester a pound weight falling through seven 

 hundred and seventy-two feet could generate enough 

 heat to raise the temperature of a pound of water one 

 degree Fahrenheit. There was nothing haphazard, 

 nothing accidental, about this ; it bore the stamp of un- 

 alterable law. And Joule himself saw, what others in 

 time were made to see, that this truth is merely a par- 



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