Methods of Theoretical Physics, 43 



mechanical example which shows great analogy with elec- 

 trical phenomena, and he wishes to bring the latter into a 

 form in which the understanding can readily grasp them *. 



In his second paper he goes still further, and from liquid 

 vortices, and friction wheels working within cells with 

 elastic sides, he constructs a wonderful mechanism which 

 serves as a mechanical model for electromagnetism. This 

 mechanism was of course mocked at by those who, like 

 Zollner, regarded it as a hypothesis in the older sense of the 

 word, and who thought that Maxwell ascribed to it a real 

 existence : this he decidedly repudiates, and only modestly 

 hopes " that by such mechanical fictions any one who under- 

 stands the provisional and temporary character of this 

 hypothesis will find himself rather helped than hindered by 

 it in his search after the true interpretation of the pheno- 

 mena.'" And they were so helped ; for by his model Maxwell 

 arrived at those equations whose peculiar, almost magical 

 power Hertz, the person most of all competent to judge, thus 

 vigorously depicts in his lecture on the relations between 

 Light and Electricity : — " We cannot study this wonderful 

 theory without at times feeling as if an independent life and 

 a reason of its own dwelt in these mathematical formulas ; as 

 if they were wiser than we were, wiser even than their dis- 

 coverer ; as if they gave out more than had been put into 

 them." I should like to add to these words of Hertz only 

 this, that Maxwell's formulae are simple consequences from 

 his mechanical models ; and Hertz's enthusiastic praise is 

 due in the first place, not to Maxwell's analysis, but to his 

 acute penetration in the discovery of mechanical analogies. 



It is in Maxwell's third important paper f and in his 

 Text-book that the formulas more and more detach themselves 

 from the model, which process was completed by Heaviside, 

 Poynting, Rowland, Hertz, and Cohn. Maxwell still uses 

 the mechanical analogy, or, as he says, the dynamical illus- 

 tration. But he no longer pursues it into detail, but rather 

 searches for the most general mechanical assumptions calcu- 

 lated to lead to phenomena which are analogous to those of 

 Electromagnetism. Thomson was led, by an extension of the 

 ideas which have already been cited, to the quasi elastic and 

 the quasi labile aether, as well as to its representation by the 

 gyrostatic-adynamic model. 



Maxwell of course applied the same treatment to other 



* Maxwell, Scientific Papers, vol. i. p. 157. 



f Maxwell. "A Dynamical Theory of the Electro-magnetic Field." 

 Scientific Papers, i. pp. 526 ; Koy. Soc. Trans, vol. 155. p. 459, 1865, 



