Mr Rudge, On the Difference of Potential, etc. 155 



On the Difference of Potential between the Terminals of a Vacuum 

 Tube. By W. A. D. Rudge, M.A., St John's College. 



[Read 4 May 1903.] 



During the course of some experiments which were undertaken 

 with the object of investigating the influence (if any) of a magnetic 

 field on the deposition of the metal volatilized from the cathode in 

 a vacuum tube, it was observed that the metal was concentrated at 

 certain places in the tube, especially along a line at right angles to 

 the direction of the field where the end of the positive column was 

 deflected upon the glass. 



It was suggested by Prof. J. J. Thomson that it would be of 

 interest to observe the effect produced by placing a piece of wire- 

 gauze in the path of the cathode discharge. 



When this was done the gauze acted as a secondary cathode, 

 and a deposit of metal was obtained from it as well as from the 

 original cathode. 



DISC 



Q#Wi) 



Fig.l. 



The tubes used were shaped as in fig. 1. The electrodes were 

 of iron or copper and the gauze was composed either of the same 

 metals as the electrodes or of different metal. The metal 

 volatilized from the primary cathode passed readily through the 

 meshes of the gauze, whether the latter was composed of the same 

 metal or of a different metal, and a deposit of both metals was 

 found on the sides of the tube beyond the gauze. 



The most interesting thing observed was that the presence of 

 the gauze caused the potential difference between the electrodes to 



