PHOSPHORESCENT ACTIVITY 295 



Analogy between Phosphorescent Molecules and 

 Radio-active Emanation from Thorium Oxide 

 and Radium, Bromide 



In the Phil. Mag. [loc. cit), the author described 

 some experiments which indicated that when a 

 discharge is sent through a gas which gives an 

 after-glow, molecules are formed that apparently 

 do not carry a free charge of electricity, unless 

 the molecules are very large, and they pro- 

 duce conductivity in the gas as they pass 

 through it. These phosphorescent molecules can 

 be made to diffuse through narrow metal tubing 

 well earthed ; but their rate of diffusion is rather 

 small, and the ionisation to which they give rise is 

 doubtless due to the radiation they emit, which at 

 a collision, as will be shown, is sufficient to pro- 

 duce ionisation. There is a striking resemblance 

 between the behaviour of these phosphorescent 

 molecules and that of the emanation from thorium 

 oxide, as was then pointed out, since the latter 

 also appear not to carry a free charge of elec- 

 tricity, but to produce ionisation in a gas through 

 which it passes. This emanation is a gas which 

 disintegrates into helium. The phosphorescent 

 glow was found to penetrate thin sheets of alu- 

 minium, but on careful examination it was dis- 

 covered that this effect was of a secondary nature. 

 If the emanation really gets through aluminium 

 the phenomenon must be one of singular import- 

 ance, since the molecules diffuse as do the 



