Phosphorescent Glow in Gases. 459 



This -would diminish the density in the neighbourhood of 

 the discharge and increase it, and therefore the pressure, in 

 other parts of the tube. The experiment of Hertz already 

 referred to indicates that the explosive effects of the discharge 

 are more vigorous at the anode than at the cathode. 



Neither the glow nor the " conductivity " accompanying it 

 can be due to "Kntladungstrahien" since these latter must 

 move with the velocity of light. But it is possible that the 

 phosphorescent particles in the after-glow are forced down 

 the tube by the explosive effects of the discharge, so that the 

 actual velocity of the glow down the tube is not due to mere 

 diffusion of the phosphorescent particles, but to the impulse 

 of the explosion as well. The conductivity, so far as can 

 be judged, is actually due to the phosphorescent particles ; 

 since the explosion will move faster and the conductivity due 

 to it would be detectable even when there is no glow, as its 

 existence is independent of the presence of the glow. The 

 same argument would hold against the "Entladungstrahlen." 



Thus it appears from the evidence we have adduced that 

 the after-glow consists of a radiation or " emanation " from 

 the spark of phosphorescent particles, which do not carry a 

 charge of electricity, and which by their presence give rise to 

 conductivity as they move through the gas. 



It might have been expected that the conductivity in the 

 glow would be destructive to itself; but, as we have seen, it 

 is only cathode-rays or negative ions when they are moving 

 with great velocities that destroy the phosphorescence ; and 

 even then it seems possible that the effect is simply to diminish 

 the duration considerably by increasing the brilliancy. 



The property which the glow thus possesses of conducting, 

 and yet of the conductivity not being influenced by a large 

 E.M.F. when the glow is first put under its influence, is verv 

 striking, and resembles in these respects the " emanation " 

 discovered by Professor E. Rutherford (Phil. Mag. Jan. 1900) 

 from thorium. 



If we view the phenomena of the conductivity of the glow 

 from this point of view, it would appear that the glow consists 

 of particles that do not carry an electric charge, but which in 

 their passage through the gas produce ionization to which the 

 conductivity observed is due. 



Section V. 



(17) There were some properties of the glow which led me 

 to suppose for some time that the glow itself was accompanied 

 by a stream of charged particles which moved down the tube. 



A tube as in fig. 5 contained a brass plug which was con- 

 nected to earth by a soldered wire. There were a number of 



2 H 2 



