180 Mr. G. J. Stoney. Note on the [May 30, 



In this connection, it is well to call to mind that phosphorescent 

 events can be excited with even greater splendour by electricity than 

 by exposure to light,* as has been abundantly shown by experiment, 

 especially by many experiments of exceptional brilliancy that have 

 been made by Mr. Crookes. 



There appears, therefore, to be no ground for the supposition which 

 has been sometimes entertained, that there is incompatibility between 

 the two facts that have been observed the fact that in these two gases 

 the ratio of the two specific heats is near its maximum value, and 

 the fact that these gases, when stimulated by electricity, furnish 

 brilliant spectra. 



Events of the Bb class in phosphorescent bodies may be made to 

 reach the intensity which enables them to emit visible radiation's in 

 any one of three ways, either 



1. By exposing the phosphorescent body to light of suitable wave- 



length and sufficient intensity ; or 



2. By exciting certain other electrical events in its neighbourhood ; 



or 



3. By raising the temperature of the whole phosphorescent body to 



a white heat. 



If the phosphorescence is excited by either of the first two of these 

 methods, the phosphorescent substance remains at a temperature as 

 tested by the thermometer, immensely short of that which would 

 enable an incandescent body to emit light of equally high refrangi- 

 bility. 



Accordingly the luminous effects within Geissler tubes do not 

 prove that the temperature of the luminous gas is very high: an 

 inference which is often erroneously drawn. In fact, Bb motions, 

 when once excited within molecules, may continue for a considerable 

 time to be more active [or, it may be, less active] than the Ba motions 

 simultaneously going on, since there is but feeble interaction between 

 them. 



If the molecule consist of but one chemical atom, there may be 

 both Ba and Bb events going on within that so-called atom. If the 

 molecule consist of two or more chemical atoms, a part of the Ba 

 events may be motions of the centres of mass of these atoms relatively 

 to one another. But this is not always the case : the bonding 

 between the atoms that form the molecule may be such that there is 

 but little of this relative motion. Accordingly, the ratio of the two 

 specific heats being large does not necessarily imply that the molecule 

 is monatomic. The inference involves the erroneous supposition 

 that there are no events going on within the molecule, and few 



* Or, rather, by electrical events other thau light ; since light is itself a mani- 

 festation of electricity. 



