328 



Dr. A. Schuster. Experiments on the 



negative electrodes are near one another, more complicated phenomena 

 arise which we need not discuss here. 



It is curious to observe the boundary of the dark space when the 

 electrode is a cylinder. Round the surface of the cylinder the boundary 

 of the dark space is a concentric cylinder. Opposite the end of the 

 cylinder it is a plane, and the plane and cylinder are united by means 

 of a surface, which is the envelope of spheres drawn with the same 

 radius from the circular edge of the cylinder as centre, that is to 

 say, by means of a part of a circular ring made up of quadrants. 

 Goldstein has described similar forms of dark spaces. The point of 

 interest, however, is this : that while on the cylindrical and plane 

 surfaces the boundary of the dark space is well marked and bright, 

 it is extremely indistinct on the circular ring. The amount of elec- 

 tricity crossing each part of the surface seems to be the same, while 

 wherever the lines of flow separate the intensity of the current must 

 decrease. We obtain in this way a smaller intensity of current at 

 the annular surface. 



Hitherto we have only assumed a certain number of particles 

 positively electrified in the immediate neighbourhood of the negative 

 electrode, and we have left it altogether undecided what these particles 

 are. But if we consider now the fact that the glow does not appear 

 opposite the positive electrode, that is to say, that while the fall of 

 potential is the same all over the surface, the flow is stronger at some 

 places than at others, we are driven to the conclusion that the flow does 

 not altogether depend on the fall of potential, and we must again look 

 for an explanation in the chemical as well as the electric forces. 

 Wherever the fall of potential is chiefly produced by the presence of 

 the positively electrified particles, which I now assume to be the 

 decomposed molecules of the gas, these will help by their chemical 

 action to decompose other molecules. Opposite the positive pole the 

 fall of potential is principally due to nearness of that electrode; 

 chemical forces are absent, and the molecules will not be decomposed. 

 This is, I believe, the explanation of the dark area. And it brings 

 with it the explanation of a large quantity of other facts, as, for 

 instance, the one which has been so long observed and well established, 

 that once a current is set up in the gas it requires a much smaller 

 electromotive force to keep it going. For the discharge, according 

 to us, will generally be introduced by a spark which must give tho 

 first supply of decomposed molecules before the continuous glow 

 discharge can establish itself. 



The effect of an increase of current on the dark area is also easily 

 explained, but I do not propose to go into details in the present 

 paper. 



If my explanation is true, we mnst expect the glow to be strong 

 between two negative electrodes, and that is tho case. 



