PHYSICAL SCIENCE IN THE NINETEENTH CENTURY 351 



first given a substantial experimental basis by the researches of 

 Benjamin Thompson, Count Rumford (1753-1814), who showed 

 that by friction of two bodies an unlimited amount of heat could be 

 generated. His results were reported to the Royal Society in 1798. 



Rumford made a cylinder of gun-metal rotate in a box contain- 

 ing water, and by the friction of a revolving borer driven by horse- 

 power the water was heated to boiling in two and a half hours. 



Deeply impressed he exclaims : 



What is heat ? Is there any such thing as an igneous fluid ? . . . 

 Anything which any insulated body, or system of bodies, can continue 

 to furnish without limitation, cannot possibly be a material substance ; 

 and it appears to me to be extremely difficult, if not quite impossible, 

 to form any distinct idea of anything, capable of being excited, and 

 communicated, in the manner the heat was excited and communicated 

 in these experiments, except it be MOTION. 



The "mechanical equivalent of heat" i.e. the work required 

 to heat one pound of water one degree was roughly calculated. 

 Epoch-making in the theory of heat were the researches of 

 Sadi Carnot (1796-1832), whose words follow: 



Wherever there is a difference of temperature followed by return to 

 equilibrium the generation of power may take place. Water vapor is 

 one means, but not the only one. ... A solid body, for example a 

 metal bar, gains and loses in length when it is alternately heated and 

 cooled, and thus is able to move bodies fastened to its ends. . . . 



The whole process he pictures as a cycle in which a certain 

 portion of the heat applied is converted into work, a certain other 

 portion being lost. Thus the new science of thermodynamics was 

 born. The thorough and complete investigation of the "me- 

 chanical equivalent of heat" belongs to J. P. Joule (1818-1889) 

 of Manchester, England, a pupil of Dalton the chemist. 



LIGHT ; WAVE THEORY, VELOCITY : YOUNG, FRESNEL. As 

 stated in Chapter XIV Huygens had supported a wave theory of 

 light, while Newton accepted an emission theory. That sound 

 was propagated by atmospheric waves was well known. There was 

 a troublesome contrast however in the phenomenon of shadows. 



