1919] on Ether and Matter 461 



times smaller in linear dimensions, is it possible to explain inertia 

 electromagnetically. But, 40 or even 20 years ago, one would have 

 said — there are no bodies of this size ; nothing can be smaller than 

 an atom ! The strange thing is that, as nearly everyone knows now, 

 bodies of this size have been discovered. They were isolated by 

 J. J. Thomson in 1899, having been gradually led up to by Crookes's 

 and many other experiments on cathode rays ; and they are shown 

 to be an apparently invisible unit or atom of electricity whose inertia 

 is wholly electric. 



The proof of this last statement I can only briefly indicate. It 

 is established by the effect of speed on electric inertia. If an electric 

 charge is moving with something approaching the velocity of light, 

 its inertia increases witliout limit ; and the formula given about 1889 

 by Heaviside, Thomson, and others, for electric inertia as a function 

 of speed, is, in its very simplest form, 



m 



= " ^ I 1 + — „ + higher powers ) 

 '6a \ "Ic^ / 



The velocity of light squared occurs in the denominator, so, before 

 we can observe the increase, enormous speeds are necessary. A 

 cannon-ball, or even the earth in its orbit, is hopelessly slow ; and 

 we know no artificial means of getting up such a speed as this last, 

 viz. about 19 miles a second. But fortunately radium does spon- 

 taneously what we cannot do, it expels electrons with something less, 

 but not very much less, than the speed of light ; and Kauffmann's 

 measure of the mass of these projectiles, thus flying at prodigious 

 velocities, confirms the theory, and removes any doubt as to the 

 reality of purely and wholly electric inertia, for electrons. 



Furthermore it was found that the very same electrons can be 

 split off or detached from any or every kind of atom, that there is 

 only one kind of negative electron ; and though at first there 

 appeared to be many kinds of positively charged particles, the 

 evidence is tending to the discovery of a single kind of positive electron 

 likewise ; so it is natural to suppose that electrons are an essential 

 ingredient in matter. And since they possess inertia, even those which 

 are clearly disembodied electric charges, it becomes possible to sur- 

 mise that in some sense, or in a certain grouping, they constitute the 

 atom, that they confer upon it the inertia with which we are familiar 

 and that in fact electric inertia is the only inertia that exists. 



Electric inertia began as the simulacrum of material inertia, it 

 has shown itself the very same thing, and it seems likely to end by 

 displacing every other kind of inertia altogether. 



This is the electrical theorv of matter. 



Assuming this theory for the present as a working hypothesis, we 

 may say that material inertia is explained electromagnetically, i.e. is 



