198 Mr. A. Schuster on the Disruptive Discharge 



close to the surface of the solid ; and if we once admit the 

 possibility of such a contact-layer which diminishes in 

 density by a reduction of pressure, some of the most 

 puzzling facts of the disruptive discharge admit of explana- 

 tion. One objection, Avhich occurs to me, must be answered. 

 It may be said that if \ is large near the surface of the solid, 

 the spark will start wherever B/A, is largest, and therefore not 

 within the condensed layer, but between it and the remainder 

 of the gas. This objection would be justified if we take the 

 discharge to be a passage of electricity between the molecules; 

 but according to the theory I advocate the dissociation of the 

 molecules may, as already explained, take place more easily in 

 the condensed layer, and probably soonest in direct contact 

 with the metal. 



Let us see how far the theory is capable of dealing with the 

 known difficulties of the discharge. I think it will be found 

 sufficient to explain the fact that when the planes or spheres 

 are near together, the normal force sufficient to produce a 

 spark diminishes with increasing distance of the conductors. 

 No explanation which has as yet been suggested can deal with 

 this fact. Prof. Chrystal, in the paper quoted above, has 

 really disposed of all suggestions except one proposed by him- 

 self, which, however, does not seem to me to be supported by the 

 observations on spheres. According to the views of this paper 

 the polarized particles within the surface-layer of the gas can 

 slide along the surface of the electrode, and will do so under 

 the action of the electric forces. They will crowd together 

 where the field is strongest, that is to say at that point at 

 which the spark is about to pass. The increased number of 

 particles will increase X, and will therefore introduce an 

 additional impediment to the formation of the discharge. As 

 the conductors are removed, the field will become more and 

 more uniform all round, the particles will no longer crowd 

 together to the same extent, and the spark will pass more 

 easily. 



The increased stress required to produce a spark when the 

 striking-distances are small are due therefore, if I am correct, 

 to the inequality of the field along the surface of the con- 

 ductor. In the case of plane surfaces which are opposed to 

 each other, the inequality lies between the back and front of 

 the plates, and the surface-particles will be drawn from the 

 back to the front. A fact which seems to me to support the 

 idea that some such thing may take place has been deduced 

 by Mr. Gr. Jaumann * from a large series of experiments. 

 * Wiener Berichte, July 1888. 



