330 Dr. A. Schuster. Experiments on the 



The Dark Space and Glow. 



I enter now into a more detailed account of the phenomena which 

 happen in the neigh bourhoood of the negative electrode. We con- 

 sider this electrode to be surrounded by a layer of electro-positive 

 particles. The molecules are decomposed partly by chemical and 

 partly by electrical forces, and the electro-negative part will be able 

 to follow the forces acting on it, and acquire a considerable velocity 

 within a small distance. This velocity will gradually be reduced by 

 impacts, and the temperature thereby raised : hence the luminosity 

 of the glow. The dark space must, therefore, be considered as the 

 region through which the greater number of atoms can freely pass. 

 But, as already observed, the dark space is itself slightly luminous, as 

 it should be. We cannot, of course, know anything at present as to 

 the mean free path of the constituents of the decomposed molecules, 

 especially as they move in a non-homogeneous atmosphere, traversed 

 from one side by the molecules coming from the positive pole, and 

 from the other by the products of decomposition. The chief difficulty 

 seems to me to be the explanation of the sharpness of the boundary of 

 the dark space in certain cases. 



Mr. Goldstein has described some interesting experiments under 

 the title of " A New Kind of Electrical Repulsion." I think that his 

 experiments admit of a very simple explanation. When the glow is 

 allowed to fall on a screen through which a small aperture is cut, its 

 rays are seen to be propagated in straight lines from the aperture. If 

 such a ray passes close to another negative electrode it is deflected. 

 This seems to me to be a necessary consequence of the fact that the 

 potential in the neighbourhood of an electrode alters very rapidly, 

 and that therefore strong forces must act on a passing particle charged 

 with negative electricity. Mr. Goldstein finds that as long as the two 

 kathodes are metallically connected the effect is the same, whatever 

 the pressure of the gas, whatever the nature of the gas, and whatever 

 the strength of the current. All these laws are easily deduced from 

 our theory. The velocity is acquired in the immediate neighbourhood 

 of the negative electrode ; if the fall of potential is increased in a 

 given ratio the square of the velocity is increased in the same ratio, 

 and throughout the path all the forces are increased also in the same 

 ratio. Hence the path must be the same, and as neither the amount 

 of electricity carried by each particle nor its mass would affect the 

 result, the total deflection of the ray is independent of the nature of 

 the gas. 



Goldstein claims to prove that the repulsion is not exerted through 

 solid substances like glass or mica, but his experiment admits of a 

 better explanation. According to Hittorf we must consider the glow 

 to be a good conductor, that is to say, metal wires which are placed 



