374 



Prof. A. Schuster. On the 



[June IB, 



positive halls in its neighbourhood, the question remains whether they 

 will collapse ultimately, whatever their distance from the discharge, 

 or whether there is a finite distance beyond which no effect can be 

 observed, even if the discharge be continued indefinitely. Without 

 wishing to express any final opinion on the point, I may yet give the 

 impression I have obtained from the experiments I have made. I 

 believe that, whenever we have a continuous and steady discharge in 

 an inclosure, however large, the complete neutralisation of all normal 

 forces on surfaces through which no current goes is only a question 

 of time, but that if there is any discontinuity in the currents (as I 

 believe is the case in all discharges at atmospheric pressure) there is 

 a definite distance (depending on the time intervening between two 

 discharges) beyond which no effect will be observed. 



The conclusion thus arrived at, which will be proved beyond 

 possibility of doubt in the second part of this paper, is this : we can 

 only have tangential forces at the surfaces of vessels enclosing a gas 

 through which a discharge is passing, provided no current crosses the 

 surface. It may be that this conclusion will appear evident to some 

 without experimental proof, but I found it necessary to obtain definite 

 evidence, because the fact itself has been constantly neglected and 

 disregarded. 



Thus, for instance, it is found that electrified bodies placed outside 

 a vessel through which a gaseous discharge is passing, do not 

 permanently affect the appearance of the discharge, and this fact is 

 commonly taken to prove that there can be no free electricity of either 

 kind in the discharge. But it follows from the surface condition at the 

 inside of the vessel, that this surface must act as a complete screen 

 between the electrified bodies placed inside and those placed outside 

 the vessel ; and the experiment therefore proves nothing. 



In similar fashion, Goldstein observed that certain actions of one 

 negative electrode on another were destroyed when a screen was 

 interposed between them. The results obtained in this paper give 

 the obvious explanation of this fact. 



After I had convinced myself that an electrified body placed in a 

 partial vacuum through which an electric current is going, has its 

 electricity quickly neutralised, it was doubtful still whether this 

 neutralisation was due to an actual discharge or merely to a covering 

 of electrified particles of an opposite sign. The question is a vital one 

 in all cases where potentials have to be measured. For we can only 

 measure potentials of a gas by measuring the potential of a metal 

 in contact with it ; and if an electrified body is covered by electrified 

 particles of a different sigD, there is a finite difference of potential 

 between the metal and the gas, and we should have to inquire care- 

 fully, in each particular case, how far such a difference would affect 

 our conclusions. 



