404 Mr. R. T. Glazebrook on the Molecular 



d¥ 

 eloctroniotive force — -=—, which arises from the electromag- 

 etc 



netic action. Thus, in a dielectric, electromagnetic phenomena 



may be explained by the strains in an elastic solid. If K be 



the specific inductive capacity of the dielectric medium, and 



B the coefficient of rigidity of the elastic solid, 



K- P ' 



If we suppose the motion such that 



dx dy dt ' 



so that the solid is incompressible, the electric displacement 



at any point in the direction of x is given by ^— V 2 ?- The 



magnetic force is equal to the molecular rotation at that point 

 in the solid. 



In the paper in the Philosophical Magazine already referred 

 to, Prof. Maxwell has shown that the state of stress which 

 exists in the magnetic field is just that which would be pro- 

 duced by vortices in an incompressible fluid. To account for 

 electricity, he supposes that there are a number of moving 

 particles between these vortices. If we suppose that in a con- 

 ductor Maxwell's moving medium behaves like a viscous fluid, 

 while in a dielectric its properties are those of an elastic solid, 

 the electrical current at any point is the "concentration " of 

 the velocity at that point, and the electrical displacement the 

 " concentration " of the displacement ; and the additional 

 " idle wheels " become unnecessary, except as explaining how 

 the vortices may be conceived to rotate. 



So far we have been considering the analogy between the 

 motion of the elastic solid and electromagnetic action. Let 

 us make the assumption that magnetic force in a dielectric 

 arises from molecular vortices in a medium which may be 

 treated like an elastic solid, and let us suppose that, owing to 

 a wave of displacement travelling through this medium, the 

 vortices are displaced, and a term arises in the kinetic energy 

 of the form 



2U(«ft>i + /3o> 2 + 7^3); 



co 1 , co 2 , co 3 being the angular velocities of the element considered 

 which arise from the displacement £, ??, J. Then Maxwell has 

 shown that the kinetic energy T per unit volume is given by 



