Rays of Positive Electricity. 361 



it would not; be legitimate to compare the intensity of the 

 phosphorescence on the willemite if the currents were very 

 different. 



The procedure was as follows: — The discharge-tube origi- 

 nally full of air was exhausted, and measurements of the 

 brightness o£ the patch of phosphorescence produced by the 

 rays for which e/m = 10 4i were made for measured values of the 

 current through the tube : the tube was then further exhausted 

 until the discharge only passed with great difficulty. Sealed 

 on to the discharge-tube was another tube containing potassium 

 permanganate: this was connected with the discharge-tube 

 by a long spiral tube dipping into a reservoir which was kept 

 filled day and night with liquid air, so as to prevent any 

 water- vapour reaching the discharge-tube. A similar spiral 

 in liquid air was placed between the discharge-tube and the 

 pump. The permanganate was heated and the tube filled 

 with oxygen ; this was pumped out and the brightness of the 

 phosphorescence measured ; the exhaustion was then carried 

 to the stage when the discharge only passed with difficulty ; 

 the permanganate was again heated and the process repeated. 

 This procedure was kept up for six days, the total number of 

 fillings with oxygen being about 70. The discharge from a 

 large induction-coil was kept running through the tube for 

 about 6 hours each day, being only stopped during the short 

 intervals when the exhaustion had been carried so far that 

 the discharge passed with difficulty, and there was a danger 

 of breaking the tube by sparking through the glass. 

 Measurements of the brightness of the phosphorescence with 

 given currents through the tube were made from time to time, 

 but there was no indication of any diminution. At' the end 

 of the run the tube was opened and hydrogen let in, when 

 again with the same current the intensity of the phosphor- 

 escent patch was the same as before. The hydrogen was pumped 

 out and helium admitted, and in this case the phosphorescence 

 seemed a little brighter than before, though the difference was 

 not considerable. There is thus no indication that the positive 

 rays are dependent upon the presence of hydrogen in the tube. 



Positive rays are very widely distributed through the tube. 

 The positive rays are to be found throughout the tube, and not 

 merely passing through apertures in the cathode and in the 

 layer of luminosity adjacent to it. The positive rays which 

 were used in the preceding experiment as well as those used 

 in all the experiments described in the previous paper, were 

 rays which had passed through an aperture in the cathode. 

 I have found, however, that positive rays are to be found in 

 all parts of the tube which have an uninterrupted view of the 

 ordinary u Canalstrahlen " or of that luminous patch next 



