THEORY OF HEAT. 



Et ignem rcgunt numeri. PLATO*. 



CHAPTER I. 



INTRODUCTION. 



FIKST SECTION. 



Statement of the Object of the Work. 



1. THE effects of heat are subject to constant laws which 

 cannot be discovered without the aid of mathematical analysis. 

 The object of the theory which we are about to explain is to 

 demonstrate these laws ; it reduces all physical researches on 

 the propagation of heat, to problems of the integral calculus 

 whose elements are given by experiment. No subject has more 

 extensive relations with the progress of industry and the natural 

 sciences ; for the action of heat is always present, it penetrates 

 all bodies and spaces, it influences the processes of the arts, 

 and occurs in all the phenomena of the universe. 



When heat is unequally distributed among the different parts 

 of a solid mass, it tends to attain equilibrium, and passes slowly 

 from the parts which are more heated to those which are less; 

 and at the same time it is dissipated at the surface, and lost 

 in the medium or in the void. The tendency to uniform dis 

 tribution and the spontaneous emission which acts at the surface 

 of bodies, change continually the temperature at their different 

 points. The problem of the propagation of heat consists in 



1 Cf. Plato, Timaus, 53, B. 



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