296 Rays of Positive Electricity. 



paper, a tube containing potassium permanganate was fused 

 on to the discharge-tube, the connecting tube being bent into 

 a long spiral and kept continuously immersed in liquid air 

 so as to prevent any water-vapour reaching the discharge- 

 tube from the vessel containing the permanganate ; there was 

 also a similar spiral immersed in liquid air between the 

 discharge-tube and the pump. The discharge-tube was 

 exhausted and the discharge persistently sent through it, the 

 gas liberated by the discharge being continually pumped out. 

 When the pressure was very low the permanganate was 

 heated and the discharge-tube filled with oxwen at the 

 pressure of several millimetres ; the discharge was kept passing 

 through this while the gas was pumped out to a low pressure, 

 when the process was repeated. After a few fillings no 

 hydrogen lines could be detected in any part of the dis- 

 charge, the spectrum was a very clean oxygen spectrum. 

 This process of filling and pumping was kept up for 6 days, 

 but with the same current through the discharge-tube I could 

 detect no change in the appearance of the phosphorescence, 

 this consisting of the two bright patches for one of which 

 el>n = 10 i , and for the other 5 X 10 3 . At the end of the run, 

 hydrogen was purposely let in the tube, and with the same 

 current the phosphorescence at low pressures was just the 

 same as before ; though in one case there was so little 

 hydrogen in the tube that it could not be detected spectro- 

 scopically, and in the other the greater part of the gas must 

 have been hydrogen. 



With reference to Professor Wien's remark that Stark's dis- 

 covery of the Doppler effect in the Canalstrahlen proves the 

 presence of positively charged atoms in the discharge, I ex- 

 pressly stated that I thought that at higher pressures and with 

 smaller electric fields than those used m my experiments, the 

 carriers of the positive electricity had for the most part a 

 mass comparable with that of the atoms of the gas filling the 

 tube. There seem to be indications that there are other 

 cases besides that of the highly exhausted tube in which the 

 carriers of positive electricity have the constancy characteristic 

 of the Canalstrahlen at low pressure. Take the case of flames 

 containing salt-vapours. The experiments of Professor H. 

 A. Wilson, Moreau and Marx have shown that it' any salt of 

 an alkali metal is introduced into the flame, the velocity of the 

 positive ion is independent of both the nature of the salt and 

 of the metal, the value under a potential gradient of 1 volt 

 per cm. being 62 cm. /sec. according to Wilson, 82 according 

 to Moreau, and 200 according to Marx. Now, if we know 

 the charge and the mass of the carrier, we can calculate the 



