1908] on the Carriers of Positive Electricity. Ill 



value of e/m for the negative particles is numerically equal to that 

 of e/m for the positive ones ; while the velocity of the negative ones 

 is slightly, but only slightly (about 15 per cent, in my experiments), 

 less than that of the positive ones. 



Experime7its with Goldstein's Double Cathodes. 



Goldstein * found that when the cathode consists of two parallel 

 plates m metallic connexion, rays other than the cathode rays proceed 

 from the space between the plates. If the plates are triangles, 

 Goldstem found that a pencil of easily deflected cathode rays starts 

 from the middle points of the sides, while pencils of uudeflected rays 

 start from the corners of the triangle. The difference in the character 

 of the rays can be strikingly shown by using helium in the discharge- 

 tube, when the rays from the corners are red and those from the 

 sides blue. I have examined the electric and magnetic deflexion of 

 these rays, using for the purpose a tube such as that shown in Fig. 3. 



Fig. 3. 



The cathode consists of two parallel triangles, and is carried by a 

 stopper working in a ground-glass tube. By turning the stopper the 

 different parts of the triangular cathode could be brought opposite 

 to the opening in the tube and the distribution of the rays round the 

 triangle studied. I found that this distribution depended a good 

 deal upon the pressure of the gas in the discharge-tube. At all the 

 pressures I tried, I found that the maximum emission of ordinary 

 cathode rays was along the line starting from the middle points of 

 the sides ; at the higher pressures, this was the only direction in 

 which the cathode rays could be detected ; at very low pressures, 

 however, rays could be detected starting from the corners of the 

 triangle, as well as from the middle points of the sides ; few, if any, 

 however, were given out in any intermediate position. With regard 

 to the positive rays, I found at all the pressures I tried that these 



* Log, cit. 



Vol. XIX. (No. 102) n 



