Kunz — Electromagnetic Emission Theory of Light. 315 



by Rontgen rajs in which the energy is distributed uniformly 

 over the wave front, suffer the same change. When liontgen 

 rays pass througli a region in which there are free electrons, 

 they tend to make the electrons move in the same direction as 

 those which produced the rays ; in addition, the velocity of the 

 electrons emitted from the metals under the action of Ront- 

 gen rays is about as high as the velocity of the primary elec- 

 trons which produced tlie liontgen beams ; tlie number of 

 electrons in the photoelectric effect depends only on the inten- 

 sity of the light, not on the color, while their velocity 

 depends only on the color and not on the intensity ; — phenom- 

 ena that we should expect from the point of view of an emis- 

 sion theory. 



Thus without considering the emission of spectral lines and 

 tlie phenomena of phosphorescence, we have a certain number 

 of independent theories assiiming a discontinuity in the emis- 

 sion of light, and a certain number of phenomena Avhich have 

 not yet been explained on the ground of the ordinary undula- 

 tory theory of light. 



That theory will finally succeed in the explanation of the 

 optical phenomena which is able to combine all experimental 

 facts under one and the same point of view; the questioii then 

 arises, which of the present theories may in the future be able 

 to give the key to the secret of the mechanism of the phenom- 

 ena of light ? 



Considering the wave theory and its electromagnetic inter- 

 pretation by Maxwell as well established, we can only expect 

 a very slight change in these theories as possible and compati- 

 ble with the explanation of some new phenomena not yet 

 explained. It seems to me as if the Faraday-Thomson con- 

 ception of electrical forces or Faraday tubes may ultimately 

 lead to a satisfactory theory of light. Sir J. J. Thomson,* fol- 

 lowing the idea of Faraday, ascribes to the lines of electrical 

 force a certain physical reality, the tubes of force being 

 endowed with mass, momentum and energy. In the paper 

 mentioned above, J. J. Thomson considers the properties of 

 the field if the electric force due to an electron is exerted in 

 only one direction. It appears that the mass of the electron 

 considered as a function of the velocity varies in the same 

 way as is required by the principles of relativity. There are 

 other ways of reasoning which lead to the same result, so that 

 even if the formula 



*Sir J. J. Thomson: On the Theory of the Structure of the Electric Field 

 and Its Application to Rontgen Radiation and to Light. Phil. Mag., xix, 

 p. 301, 1910. 



