376 Dr, G. J. Stoney on the 



or in some other form through the aether, or in some other 

 way, as, for example, from a disruption of chemical bonds. 

 But though the encounters would be unequal to the task of 

 arousing them from a state of quiescence, they, on their side, 

 if brought into a state of activity by some other agency may 

 be able to impart energy to A and Ba events, which are the 

 proximate dynamical cause of the ordinary gaseous laws. 

 This peculiar behaviour, whereby energy passes more freely 

 one way than in the opposite direction, is a dynamical conse- 

 quence of the linkage between molecules to which Professor 

 FitzGerald has called attention. Owing to this linkage the 

 encounters may have to produce an effect on a platoon of 

 molecules in order to affect the B& motions of any one of 

 them ; and as these encounters are many and irregular their 

 aggregate effect can be but small wherever the linkage is 

 effective ; while, as regards the reaction, the body of linked 

 B5 motions act in each encounter on the A or B« motions of 

 a single molecule and may produce a considerable effect on 

 them. The dynamical relation is analogous to what would 

 prevail between a number of light pellets bombarding a 

 massive body on all sides. Their effect on the motion of the 

 massive body is small, while its effect on their motions is 

 large. It seems to be in this way that radiant heat can warm 

 a gas through the lines in its spectrum, very slowly in the 

 more transparent gases, less slowly in coloured gases. 



An electron within a molecule may be associated with 

 either its Ba or its B6 motions. Thus, when a phosphorescent 

 body has been exposed to suitable light, it is an electron 

 associated with Bfr motions that is primarily acted on by the 

 sether. Now phosphorescence is a very prevalent property 

 of bodies, inasmuch as it has been ascertained by the phos- 

 phoroscope that a large proportion of the substances about us 

 are phosphorescent. And although most of them, after being 

 stimulated, retain their power of radiating light for but the 

 fraction of a second, there are some phosphorescent sub- 

 stances in which it lasts for hours. It must be remembered 

 that any fraction of a second which the phosphoroscope can 

 detect is an immense duration as regards the rapidity of 

 molecular events. Accordingly it is with B& events that we 

 are here dealing. All B6 events are sluggish from the 

 molecular standpoint in handing over any excess of energy 

 they may possess, either directly or indirectly, to the motions 

 of translation of the molecule. But viewing the matter from 

 our human standpoint, it is convenient to distinguish those 

 which can accomplish this in a small fraction of a second 

 lVoni tho^e which take so much longer a time that we can 



