WHAT IS ELECTRICITY? — HEYL 225 



motion through the ether, t-o flatten into an obhite spheroid. Exper- 

 iments by Bucherer -<^ in 1909 were interpreted as favoring the 

 hypothesis of Lorentz. 



But in 1927 a new line of experimental evidence as to the structure 

 of the electron was opened up by Davisson and Germer,*'^^ soon fol- 

 lowed by G. P. Thomson.-^ These investigators found in brief, 

 that electrons (of the negative variety) might be scattered by re- 

 flection or diffracted by passage through very thin films of metal 

 in such a way as to suggest that an electron is at least as much like 

 a little bunch of waves as it is like a particle, and that neither aspect 

 can be ignored. 



This is well brought out by G. P. Thomson's diffraction rings. 

 The electron must have a wave aspect, or there would be no inter- 

 ference pattern; it must have a charged particle aspect, or the 

 whole ring system would not be deflected by a magnet, as it is found 

 to be. The whole situation, in fact, had been foreshadowed theo- 

 retically by the wave mechanics of de Broglie and Schrodinger. 



A number of explanations have been offered for this dual be- 

 havior. Perhaps the most completely worked out is that of J. J. 

 Thomson,-^ based upon the diffraction rings obtained by his son, 

 which lend themselves particularly well to theoretical treatment. 

 On this view the electron is associated with and accomjjanied by a 

 group of waves which guide and direct its motion. Now it was 

 found by a study of the speed of the electrons and the associated 

 wave lengths in the diffraction rings that a curious and complicated 

 relation existed between these quantities. If u is the velocity of an 

 electron and A its associated wave length, this relation is : 



in which c is the velocity of light and G is a constant. 



But this, as J. J. Thomson shows, is exactly the relation that should 

 hold for the group speed of electromagnetic waves in a medium such 

 as the Keimelly-Heaviside layer, containing a multitude of electric 

 charges, positive and negative. 



J. J. Thomson therefore suggests the following structure for the 

 negative electron: 



I. A nucleus which, like the older concept of the electron, is a 

 charge of negative electricity concentrated in a small sphere. 



II. This nucleus does not constitute the whole of the electron. 

 Surrounding it there is a structure of much larger dimensions which 



2" Bucherer, Ann. Phys., vol. 28, p. 513; vol. 29, p. 1063, 1909. 

 " Davisson and Germer, Pliys. Rev., vol. 30, p. 705, 1027. 

 *2 Thomson, G. P., Proe. Roy. Soc, vol. 117, p. 600, 1928. 



2» Thomson, J. J., Beyond the Electron, Cambridge Univ. Press, 1928; Phil. Mag., vol. 6, 

 p. 1254, 1928. 



