ON THE PHYSICAL VIKW OF NATL'KE. 1 1' 1 



extensive class of phenomena which are not produced 

 by mechanical forces, but which result solely from the 

 presence and accumulation of heat. This part of natural 

 philosophy cannot be brought under dynamical theories ; 

 it has principles peculiar to itself, and is based ui^m 

 a method similar to that of the (^ther exact sciences.^ 

 . . . The dilatations, indeed, caused by the repulsive 

 force of heat, the observation of which dilatations serves 

 as a measure of temperature, are dynamical effects ; but 

 it is not these dilatations which we calculate when we 

 investigate the laws of the ])ropagation of heat." " He 

 proceeds to Imild up this new science "upon a very 

 small nvmiber of simple facts, of which the causes are 

 unknown, but which are gathered by observation and 

 confinned by experiments," ^ and he thus arrives at 

 certain general relations, expressed in the form of equa- 

 tions, which are different from, though analogous to, and 

 not less rigorous than, the general equations of dynamics. 

 One of the great experimental facts upon which Fourier 

 bases his theory of the propagation (i.e., the conduction 

 and radiation) of heat is this, that all motion of heat 

 depends on differences of temperature. He examines 

 how differences of temperature are equalised and de- 

 duces the law of the flow of heat."^ Although he does 



'Fourier, ' Theorie analytique,' | zig, 1896), pp. 78, &c'., 116 sq/j. 

 p. 13. '^ Ibid., p. 14. I Every studeut of pliy.sic.s should 



•* Ibid., pp. xi, 18, 39. read the chapters referring to this 



* I cannot here omit to jxtint out 

 how elegantly Prof. Mach has trans- 

 lated into the language of common- 

 sense the whole process of Fourier 

 for establi.shing the fundamental 



subject. The mathematical for- 

 mulie will thus l)ecome living to 

 him ; but he will also see how 

 necessary the abstract mathematical 

 expression of common-sen.se cou- 



equation of the theory. See his ' ceptions is in order to avoid false 

 'Priucipien der Warmelehre' (Leip- | reasoning. 



