Electrodynamic Equations of a Moving Material Medium, $c. 365 



smaller particles, as lias already "been suggested by J. J. Thomson 

 from entirely different evidence ; but the results are too few to make 

 further speculation on their meaning of much value. 



" Note on the Complete Scheme of Electrodynamic Equations 

 of a Moving Material Medium, and on Electrostriction." 

 By JOSEPH LARMOR, F.R.S., Fellow of St. John's College, 

 Cambridge. Received May 17, Read May 26, 1898. 



This note forms a supplement to my third memoir on the " Dynam- 

 ical Theory of the ^Ether,"* to the sections of which the references 

 are made. 



1. It is intended in the first place to express with full generality 

 the electrodynamio equations of a material medium moving in any 

 manner, thus completing the scheme which has been already devel- 

 oped subject to simplifying restrictions in the memoirs referred to. 

 To obtain a definite and consistent theoretical basis it was necessary 

 to contemplate the material system as made up of discrete molecules, 

 involving in their constitutions orbital systems of electrons, and 

 moving through the practically stagnant aether. It is unnecessary, 

 for the mere development of the equations, to form any notion of 

 how such translation across the aether can be intelligibly conceived : 

 but, inasmuch as its strangeness, when viewed in the light of motion 

 of bodies through a material medium and the disturbance of the 

 medium thereby produced, has often led to a feeling of its impossib- 

 ility, and to an attitude of agnosticism with reference to eethereal 

 constitution, it seems desirable that a kinematic scheme such as was 

 there explained, depending on the conception of a rotationally elastic 

 tether, should have a place in the foundations of aether- theory. Any 

 hesitation, resting on a priori scruples, in accepting as a working 

 basis such a rotational scheme, seems to be no more warranted than 

 would be a diffidence in assuming the atmosphere to be a continuous 

 elastic medium in treating of the theory of sound. It is known that 

 the origin of the elasticity of the atmosphere is something wholly 

 different from the primitive notion of statical spring, being in fact 

 the abrupt collisions of molecules : in the same way the rotational 

 quality of the incompressible aether, which forms a sufficient picture 

 of its effective constitution, may have its origin in something more 

 fundamental that has not yet even been conceived. But in each 

 case what is important for immediate practical purposes is a con- 

 densed and definite basis from which to develop the interlacing 

 ramifications of a physical scheme : and in each case this is obtained 

 by the use of a representation which a deeper knowledge may af ter- 

 * ' Phil. Trans.,' A (1897). 



