CONDUCTION THROUGH GASES 153 



opposite signs. Here we have two charges ; but, 

 for an isolated charged body, the Hnes of electric 

 force must evidently be radial. 



Now Thomson explained electro-magnetic 

 momentum as an effect of the Faraday tubes of 

 force in pulling after them as they move some of 

 the surrounding medium. A solid body moving 

 through water drags some of the liquid with it, 

 and, in this way, its effective mass is increased. 



« » 



\ 



1 . ' ' 



-. *«. \ \ • ; / / / / 



::::--:-v>n\; ; / / / / /' 

 — :::-.>\\\ i ; / / / / / 



,---- .'■■.''>7'^W^r\ :.^^>v77?n^?^^V':--. - -- 



.'- .-'.'// /,*;\ \-.\ •.;-.;- ---''•'-''//! 1 \^ ^'v '% ^-. 



/ / / / ; ; \ \\ v.-« ' ,-,'/;. . *; ^ \ \ 



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Fig. 31. 



A vortex filament, too, carries with it some of the 

 fluid of which the vortex is composed. So with 

 the F'araday tubes if we look on them as physical 

 realities. Maxwell showed that the same medium 

 would explain both light and electric waves, and 

 we may perhaps, as an illustration, think of tubes 

 of force as vortex filaments in the luminiferous 

 aether. We may then suppose that they move 

 some of the surrounding aether with them. If the 

 aether possess mass, it will endow the moving 



