[ 727 ] 



LXVI. Xote on the JEther and on the Hypothetical 

 Magnetic Flow. By Sir Oliver Lodge *. 



IX connexion with my paper, on the Inertia of iEther 

 per unit volume, in the April number of the Phil. Mao-., 

 Professor Hicks, of the University of Sheffield, has kindly 

 called my attention to his Address to Section A of the 

 British Association in 1895 at Ipswich, wherein he gives 

 some reasons for conjecturing an atherial density not much 

 less than that of water ; and he likewise postulates for the 

 aether an intrinsic mean square velocity about twice the speed 

 with which it transmits light. I would have referred to these 

 confirmatory speculations, in the Appendix to my paper, if 

 I had remembered them. 



Concerning a hypothetical petherial flow along magnetic 

 lines of force, suspected by some mathematical physicists — 

 whence we get the term " permeability/'' — the deduction from 

 my series of experiments demonstrating the lack of all per- 

 ceptible influence on the speed of light, as recorded in the 

 paper above referred to, was to the effect either that the 

 magnetic flow was very slow or else that it was actually zero. 



My conception of the aether involves the supposition that 

 as regards locomotion it is quite stationary, although full of 

 constitutional rotational energy ; and the hypothetical mag- 

 netic flow, though auxiliary, was not an essential part of my 

 doctrine concerning the substantiality and extraordinary 

 massiveness of every portion of the aether of space. So I am 

 rather pleased to find in Professor Hicks's Address a footnote 

 containing a simple and ingenious proof that whatever be the 

 kinetic nature of a magnetic field, it cannot consist of mere 

 irrotational setherial streaming. The argument may be para- 

 phrased thus : — A conductor moving across a magnetic field 

 generates an E.M.F. If the magnetic field itself were nothing 

 but locomotion of aether along the lines of induction, then that 

 motion could be compounded with the motion of the conductor, 

 so as to be equivalent to a stationary conductor in a field 

 inclined at some different angle. But in a stationary con- 

 ductor no E.M.F. is generated. Therefore when a conductor 

 moves so as to generate E.M.F. it must cut a structure of 

 some kind, not a mere flow. The suspected magnetic 

 streaming therefore — though not negatived — must be regarded 

 as a superfluity, and becomes improbable. 

 University of Birmingham, May 1, 1907. 



* Communicated by the Author. 



