62 Sjjeyers — Heat of a Change in Connection with 



znr Lebensaufgabe gemacht hat, muss an irgend einer Stelle 

 seiner Yergangenheit den Tribiit zahlen." 



The barrenness of the notion of chemical energy shows how 

 useless to seek an explanation of chemical action inside the 

 reacting system. How very productive was Faraday's treat- 

 ment of electricity and magnetism ! Outside the charged 

 sphere, the wire, and the magnet, are the energies. 



Just so in chemical reactions, let us say, for example, those 

 involving heat, outside the material part of the system is where 

 we are to find the source of the heat. 



Consider an infinite uniform electric field whose dielectric 

 constant is K^,, whose electric intensity is E^, and whose dielec- 

 tric displacement is D^. Then the energy W,, in a volume v^ is 



or, since in a uniform field 



we have 



W. = -^ 'V (1) 



JSTow introduce into the infinite field a sphere of radius l 

 and of volume v^ and whose dielectric constant is K^. Since 

 the field is infinite, we consider that no change is made in the 

 total energy of the field outside the sphere, for there is nothing 

 to mamtam a change in the intensity of the field if it is not 

 directed, and if it is directed any change produced on one side 

 of the sphere is balanced by an equal opposite change on the 

 other side. Inside the sphere, the electric force is changed to 

 Ej^ such that 



-p _ 3K„E^ 



the moment M of the imaginary doublet representing the 

 sphere being 



^ E„(K.-K„) 

 K, + 2K, 



Substituting 2 in 1, we have for the electric energy Wj in the 

 sphere 



_jk;e; 



* Elements of Elect, and Mag., J. J. Thomson, chap. v. (1895), 



