AND MODERN PHYSICS. 177 



of which would in sonic respects closely resemble 

 those of tho ether; from this model ho deduced, 

 among other things, tho important fact that electric 

 waves would travel outwards with the velocity of 

 light Other such models have been devised since 

 his time to illustrate the same laws. Prof. Fitzgerald 

 has actually constructed one of wheels connected 

 together by elastic bands, which shows clearly the kind 

 of processes which Maxwell supposed to go on in a 

 dielectric when under electric iorcc. Professor Lodge, 

 in his book, " Modern Views of Electricity," has very 

 fully developed a somewhat different arrangement of 

 cog-wheels to attain the same result 



Maxwell's predictions as to the propagation of 

 electric waves have in recent days received their full 

 verification in tho brilliant experiments of Hertz and 

 his followers; it remains for us, before dealing with 

 these, to trace their final development in his hands. 



The papers we have l>een discussing were perhaps 

 too material to receive tho full attention they 

 deserved ; the ether is not a series of cogs, and elec- 

 tricity is something different from material idle 

 wheels. In his paper on "The Dynamical Theory of the 

 Electro-magnetic Field, 11 Phil. Trans., 18G4, Maxwell 

 treats the same questions in a more general manner. 

 On a former occasion he says, " I have attempted to 

 describe a particular kind of motion and a particular 

 kind of strain so arranged as to account for the 

 phenomena. In the present paper I avoid any 

 hypothesis of this kind ; and in using such words as 

 electric momentum and electric elasticity in reference 

 to tho known phenomena of the induction of currents 

 L 



