528 HISTORY OF THERMOTICS. 



Sect. 3. Verification of the Doctrines of Conduc- 

 tion and Radiation. 



THE interior and exterior conductivity of bodies are 

 numbers, which enter as elements, or coefficients, 

 into the mathematical calculations founded on the 

 doctrines of conduction and radiation. These co- 

 efficients are to be determined for each case by 

 appropriate experiments ; when the experimenters 

 had obtained these data, as well as the mathema- 

 tical solutions of the problems, they could test the 

 truth of their fundamental principles by a com- 

 parison of the theoretical and actual results in 

 properly-selected cases. This was done for the law 

 of conduction in the simple cases of metallic bars 

 heated at one end, by M. Biot 7 , and the accordance 

 with experiment was sufficiently close. In the 

 more complex cases of conduction which Fourier 

 considered, it was less easy to devise a satisfactory 

 mode of comparison. But some rather curious re- 

 lations which he demonstrated to exist among the 

 temperatures at different points of an armille, or 

 ring, afforded a good criterion of the value of the 

 calculations, and confirmed their correctness 8 . 



We may therefore presume these doctrines of 

 radiation and conduction to be sufficiently esta- 

 blished; and we may consider their application to 



" Tr. de Phys. iv. 671. 



8 Mem. I vst. 1819, p. 192, published 1824. 



