258 



Mr. M. N. Shaba on Maxwell's Stresses. 



of the present paper is to show that the stresses cannot 

 account for the energy of electrification, i£ the medium is to 

 be regarded as an elastic solid. 



4. The energy of a charged system can be expressed as a 

 volume integral, 



Maxwell * states that the quantity W may be interpreted 

 as the energy in the medium due to the distribution o£ 

 stresses ; but the statement is not proved. The only rational 

 meaning which we can attach to this assertion is that the 

 energy of electrification arises from the elastic displacement 

 of sether particles. I am not aware whether any other inter- 

 pretation has been or can be given to Maxwell's statement, 

 but it has generally been taken in this sense, though Maxwell 

 himself is rather vague on the point. We should naturally 

 expect that energy calculated on this understanding would 

 lead to the expression (5), but that this is not the case will 

 be presently shown. 



5. If u, v, w be the elastic displacements of a particle of 

 the dielectric medium, the energy of deformation or the 

 train-energy function is 



state 



w 



initial state 



final state 



+ 



f ff (KM + Y V B v + Z v 8w)dS, 



initial state 



and this can be shown to be equivalent to 



(6') 



tfff« 



+ Y y e yy + Z z e 2Z -f Xytfay + Y z e yz + Z x e zx )dx dy dz> 



Assuming the aether to be isotropic and to behave as an elastic 

 solid, we can put 



1 



e yy 



and 



E 



e X y 



J 



1 —a —a 

 — a 1 — <t 

 — a —<r 1 



X^ JLz Li x 



* ' Electricity and Magnetism/ p. 165. 



x 3 



