20-A Prof. L. T. More on the 



existence of aether stresses, wo can still avail ourselves of all 

 the mathematical transformations by which the application 

 of the formula may be made easier. We need not refrain 

 from reducing the force to a surface-integral, and for con- 



t? > t? " 



venience sake we may continue to apply to the quantities 

 occurring in this integral the name of stresses. Only, we 

 must be aware that they are only imaginary ones, nothing 

 else than auxiliary mathematical quantities." It is also, 

 I think, safe to say that Sir J. Larmor believes in the 

 fictitious character of the Maxwellian stresses. Does not 

 this also lead to the idea that electrons, which are disem- 

 bodied electricity and which produce these imaginary stresses, 

 are themselves imaginary ? 



There is at present a controversy whether these electrons 

 are rigid or deformable. The only consequence of these two 

 views necessary to comment on now is a very pertinent 

 remark of Hr. Abraham*, that if the electron be deformable, 

 work will be required to effect this deformation, and to avoid 

 contradiction with the law of conservation of energy, thj 

 electron must possess internal potential energy. This 

 opinion of Hr. Abraham is almost impossible to avoid. To 

 provide the electron itself with this kind of energy is to deny 

 its character as the fundamental and indivisible unit of 

 matter, for a body having potential energy must contain 

 mutually reacting parts which may themselves be considered 

 as units of a lower order; nor will many approve of 

 M. Poincare's rather embarrassing suggestion, that the aether 



& t>t? ' 



may be a great and inexhaustible store-house of energy, 

 drawn on at will by the electron each time it moves. This 

 idea will hardly be taken seriously, as the assumption of 

 unlimited energy existing in a fictitious aether is in no sense 

 a scientific notion ; it contradicts the prevailing idea of the 

 inertness of the aether and makes of it a sort of dens ex 

 machina which interposes to help us out of difficulties. And 

 indeed the electromagnetic aether, without material properties 

 other than imaginary stresses, is an explanation more difficult 

 to grasp than the phenomena of radiant energy which require 

 explanation. 



Such a revolution in the nature of aether requires a like 

 one in our ideas of matter. The most notable effort in 

 theoretical physics, at the present time, is the hypothesis that 

 the ultimate element of matter is not a material atom, a sort 

 of microcosm of sensible matter, but a free electrical charge, 

 considered to be an entity for the purpose ; added to this are 

 the dependent ideas that inertia and all other properties of 

 * Theorie der Elekirkitcit. II Eap. '3. Leipzig 1905. 



