400 Sir Oliver Lodge on the 



It is admitted that each negative electron has a certain 

 intrinsic inertia or massiveness, dependent upon the amount 

 of electricity which constitutes it, and on its size when 

 pictorially represented as like a charged sphere ; the mass 

 being constant for all ordinary ranges o£ speed. 



The simplest way of illustrating such a mass is to treat 

 it as if it were a sphere of radius a moving through a simple 

 irrotational perfect liquid, of density p, which it merely 

 displaces. 



The aether being supposed incompressible, as stated above, 

 the density inside and outside the sphere must, on the 

 simplest hypothesis, be assumed the same. And accordingly 

 the total effective mass of the moving body is half as much 

 again as the mass of the sphere itself, viz. 27rpa d ; since in 

 such a case the body is known, from ordinary hydrodynamics, 

 to behave as if it carried half its bulk of fluid with it, while 

 all the rest was annihilated. 



That is the simplest mode of regarding the matter. 



7. But it is known that the apparent mass of an electric 

 charge really resides in the space outside it ; being due to the 

 circular magnetism which surrounds its path. If its speed 

 is it, the intensity of magnetic field at any place rd, due to 

 the motion, is, in every system of units, 



Tj eu sin 6 



[Parenthetically we may here observe, without any hypo- 

 thesis, how enormous is the magnetic intensity immediately 

 surrounding the equator of an electron, moving along an 

 axis at say g^th the speed of light. It is no less than 10 15 

 c.G.s. units. At a third the speed of light, even in the 

 completer theory of which the above is the dominant term at 

 ordinary speeds, it is still not appreciably more than 10 16 ; but 

 it begins to run up suddenly towards infinity when the velocity 

 of light is closely approached. The reason probably being 

 that it is then no longer a small fraction of the intrinsic 

 rotational energy of the sether itself.] 



8. Now mathematical speculation has suggested that there 

 is an aetherial flow or circulation along lines of magnetic 

 induction, which are well known to be always closed curves ; 

 and it is natural to assume that the energy of the field may 

 be represented by the energy of this motion. Denote the 

 speed of this hypothetical aather-drift by w, then the energy 

 per unit volume is expressible in two equivalent ways, namely, 



i 2 i ^H 2 



as 4pmt, and as - 



C57T 



