468 Sir Oliver Lodge on a jjossible means of determining' 



If that were true it would follow that the elasticity effective 

 in radiation must be o£ the order 10 33 c.g.s , so that the- 

 ratio of the two may be 9 x 10 20 , the square of the velocity 

 of light. 



The problem before us is to find out if any experi- 

 mental means can be devised for putting this hypothesis or 

 assumption to an experimental test, so as either to confirm 

 or correct it. 



Now we know that magnetic lines of force, unlike electric 

 lines of force, are always closed curves ; hence it is possible 

 for something material to flow along them continuously. 

 Round every electric current there is magnetic circulation ;. 

 is it possible that this may be setherial circulation ? 



As I understand Larmor's theory of magnetism (see for 

 instance pages 84 & 336 of his book, ' iEther and Matter/ 

 See also the Phil. Mag. for April 1907, p. 500) it postulates 

 a flow of something along magnetic lines. A magnetic 

 field is a seat of kinetic energy, while an electric field 

 is a seat of potential energy ; the interaction of the two 

 fields is responsible for wave propagation. 



If any aether is really flowing along the lines of a magnetic 

 field, and if it has a real density, it is natural to attribute 

 the energy of the field to the kinetic energy of this flow; and 

 to identify the self-induction of an electric current with the 

 surrounding setherial inertia. 



That, at any rate, is the working hypothesis which I 

 propose to make ; and if we could determine the velocity of 

 the flow in a given field, we should therebv determine the 

 jetherial density. That is an experiment the possibility of 

 which I propose to consider. 



The obvious suggestion is to split a beam of light and send 

 each half in opposite directions round a closed optical circuit 

 in such a way that when they meet they shall form inter- 

 ference bands. Examine these bands in a micrometer, then 

 magnetize the circuit in such a way that the lines of force 

 run parallel to or coincident with the beam of light, and 

 watch for a shift of the bands. 



A circuit shaped like an equilateral triangle, with mirrors 

 at the corners, would seem the best for this modification of 

 Fizeau's classical experiment on the effect of moving water. 



In 1892 & 1893 at Liverpool I performed carefuilv an expe- 

 riment of this kind (see Phil. Mag. April 1907, p. 495), using 



