156 



Mr Rudge, On the Difference of Potential 



be largely increased when the discharge was passing through the 

 tube, the potential being inferred from the length of spark between 

 the knobs of a spark micrometer joined in parallel with the tube. 



The potential varied with the nature of the metal composing the 

 gauze and also with the mesh or area of aperture. 



A series of experiments was then undertaken in order to 

 investigate the relation between the nature of the metal and the 

 increase in potential of the tube. This increase was very great, 

 the potential being from two to six times that of a similar tube 

 without gauze and at the same degree of exhaustion. 



Instead of wire-gauze it was found more convenient for 

 purposes of comparison to use discs of metal perforated with the 

 same number of holes and drilled with the same drill, so that the 

 aperture areas were the same in each case. The discs were fixed 

 in the tubes by means of two wire rings of the same metal as the 

 discs. 



In order that the potentials of two tubes with discs of the 

 same or different metals might be compared at the same pressure 

 an apparatus was constructed as in fig. 2. 



The vertical tubes were about 20 cm. in length and 1*5 cm. in 

 diameter. On the tubes used at first the electrodes were attached 

 to brass caps which were fastened to the tubes by sealing-wax. 



