PHOSPHORESCENT ACTIVITY 297 



appear to be any reason to suppose that there 

 should not be vibrations of a much more rapid 

 period than those which have yet been observed, 

 and to ignore this fact is to obscure our minds to 

 the possibilities of discovering phenomena which un- 

 doubtedly exist and which we may be sure perform 

 an important part in the phenomena of Nature. 



Thus the well-known model of fluorescence sug- 

 gested by Stokes can be applied in another way 

 than that proposed by him to the sether so as to 

 show that if the vibrations of the electrons on the 

 atoms are more rapid than a certain period, the 

 minimum period which the sether — as a solid or 

 fluid with ultimate molecular structure — can trans- 

 mit, the energy of the vibrations, instead of being 

 radiated away, becomes confined to the neighbour- 

 hood of the atom and its interior. The solution of 

 one of the great difficulties in the kinetic theory 

 pointed out by Lord Kelvin and FitzGerald is greatly 

 facilitated by this conception. " The average efi'ect 

 of repeated mutual collisions must be to convert all 

 the energy of translation into shriller and shriller 

 vibrations of the molecules, and when each molecule 

 is a continuous elastic solid it is rigorously demon- 

 strable that the whole translational energy must 

 ultimately be transformed into vibrational energy 

 of higher and higher nodal sub-divisions." This 

 seems to be correct, for instance, in the case of 

 billiard balls, since they have an infinite number of 

 degrees of freedom. Hence the energy of the vibra- 

 tions when the frequency becomes too rapid to be 



