506 The Density of the Mther. 



known) by an irrotational motion of the aether having velocity- 

 potential of form A log li ; thus in its aggregate amount it involves 

 no elastic reaction, and disappears spontaneously by irrotational 

 flow when the electron has passed on. Thus, even with much lower 

 effective inertia of the aether, the passage of the electron would not 

 involve any permanent elastic dislocation in its surroundings, though 

 very near it there might be increased elastic reaction equivalent to 

 increase of its effective size : it being understood that so long as we 

 do not know how the core of the electron is keyed together, the 

 nature of its own penetration through aether — whether it be ana- 

 logous to the motion of a vortex ring or otherwise — is beyond our 

 cognisance, and must remain a matter of immediate hypothesis." 

 Prom this note a deduction at once follows, thus : — 

 The angular displacement at any distance h from path of electron, 

 after it has passed, is <p = 2ke/h? ; so the linear velocity of aether 

 circulation at that place, while the electron is passing, is 



. TT l-eu . 



Everywhere, except close to an electron, <p is extremely small; 

 but I see no reason for attributing to tf> any but a finite value (i. e. 

 something comparable to a radian) quite close to an electron. 

 If that is permissible, the above little calculation is confirmatory 

 of the hypothesis that iv , the rotation speed round the equator, 

 is of the same order as u, the translation speed of an electron. 

 But Larmor supposes that the angular shift must be small every- 

 where. In that case iv would be less than u, and the estimate of 

 setherial density, together with the values of the other extra- 

 ordinarily large quantities in this paper, would have to be corre- 

 spondingly increased. 



Appendix C. 



The following brief note from Professor J. J. Thomson is of 

 special interest : — 



" Cavendish Laboratory, 13 March, 1907. 



" Many thanks for letting me see the proof of your paper. I 

 have held for some time the view that the mass of bodies is the 

 mass of aether they carry along with them, and that this mass can 

 be carried along by the lines of electric force as well as the bodies 

 these lines connect. The amount carried by the small negative end 

 is small compared with that carried by the lines of electric force, 

 while the amount of the aether carried by the large positive end 

 exceeds that carried by the lines ; hence the mass of the corpuscle 

 seems wholly electrical, while that of the atom does not. I think, 

 however, both masses are identical in origin, being masses of portions 

 of aether. I went into this view at some length in my ' Electricity 

 and Matter,' and have been confirmed in it by later consideration. 

 Of course it requires a very dense aether." 



It is satisfactory thus to find a fair consensus of leading opinion 

 in favour of some such proposition as I have endeavoured to argue 

 out, and make more precise, in the above paper. 



