524 HISTORY OF THERMOT1CS, 



and Poisson and M. Cauchy had consulted the ma- 

 nuscript itself. 



It is not my purpose to give, in this place 4 , 

 an account of the analytical processes by which 

 Fourier obtained his results. The skill displayed 

 in these Memoirs is such as to make them an ob- 

 ject of just admiration to mathematicians ; but they 

 consist entirely of deductions from the fundamental 

 principle which I have noticed, that the quantity 

 of heat conducted from a hotter to a colder point 

 is proportional to the excess of heat, modified by 

 the conductivity, or conducting power of each sub- 

 stance. The equations which flow from this prin- 

 ciple assume nearly the same forms as those which 

 occur in the most general problems of hydrodyna- 

 mics. Besides Fourier's solution, Laplace, Poisson, 

 and M. Cauchy have also exercised their great ana- 

 lytical skill in the management of these formulae. 

 We shall briefly speak of the comparison of the 

 results of these reasonings with experiment, and 

 notice some other consequences to which they lead. 

 But before we can do this, we must pay some 

 attention to the subject of radiation. 



Sect. 2. Introduction of the Doctrine of Radiation. 



A HOT body, as a mass of incandescent iron, emits 

 heat, as we perceive by our senses when we ap- 

 proach it; and by this emission of heat the hot 



4 I have given an account of Fourier's mathematical results 

 in the Report of the British Association for 1835. 



