160 



Mr Rudge, On the Difference of Potential 



The length of the dark space could not be determined with 

 this tube, but it was probably about 2 to 3 cm. 



(1) 



(2) 



PHOS 



GLASS 



Cm.1 2 3 



When the disc was actually behind the point cathode (the hole 

 in the disc was large enough to pass over the glass covering the 

 cathode) the potential was rather more than when at the central 

 parts of the tube, and a sudden rise occurred just as the disc 

 came over the cathode. The phosphorescence (A, fig. 3) which 

 previously existed just opposite the cathode was thrown down 

 the tube, the aperture pulling the rays together to form a cone 

 having its apex at the cathode (B, fig. 3), and the base of the 

 cone, i.e. the position where the phosphorescence of the tube 



