PHOSPHORESCENT MOLECULES 287 



The phosphorescent molecules produce ionisation 

 in the gas as they pass through it, probably by 

 the radiation they emit, which at molecular dis- 

 tances should exercise a sufl&cient influence upon 

 neighbouring molecules so as to break them up 

 into ions. The subsequent collisions between these 

 and the glowing molecules would keep up the 

 phosphorescence, although, if the number of such 

 collisions is too numerous, the molecules would be 

 completely broken up and the glow destroyed. 

 The radiation from the glowing molecules would, 

 however, be sufficient to mitigate the efi"ects of 

 ordinary collisions. 



That Separate Large Luminous Molecules Exist 

 in Flames 



We have seen that from considerations as to the 

 specific inductive capacity of gases, Thomson has 

 deduced by means of a formula of Lorenz that in a 

 luminous gas the spectral lines are not given out by 

 every molecule, but only by a comparatively small 

 number of systems formed in some way out of the 

 molecules, perhaps by aggregations of greater com- 

 plexity than the molecules. He considers that the 

 systems which give out one line may be different 

 from those which give out the others. These 

 points, quite independently, support the theory of 

 molecular aggregates in luminosity worked out in 

 this book, some of the experimental evidence for 

 which has already been described. Since his ob- 



