Light Absorption and Fluorescence. 637 



then it is to be expected that there should also exist the 

 various possibilities 



(n — l)v x = vi, 



(n — 2)v x = v 2 , 



(n — 3>a.= v 3 , 



&c. 



That is to say, there should exist possibilities of the 

 absorption by one and the same substance of light of 

 frequencies v 1} v 2 , v 3 , &c, and that each quantum of energy 

 hv Jw 2 , I1V3, &c. thus absorbed should be evolved as 

 h(n—l)v xy h(n — 2)v x , h(n-3)v x , &c. quanta of infra-red 

 radiation respectively. 



Since 



Vq— v 1 = v 1 — v 2 = v 2 — v 3 = = v x , 



we should expect to find evidences of absorption bands with 

 constant frequency differences exhibited by one and the same 

 substance. Inasmuch as such constant frequency differences 

 do exist between the absorption maxima, the deduction 

 made from the energy quantum theory is experimentally 

 verified. 



Again, the absorption and fluorescent maxima appear to 

 give a means of determining the values of v u v 2 , z> 3 , &c. 

 Since the differences v l — v 2i v 2 — v Zi &c. equal v x , they should 

 equal the frequency of a band in the infra-red. Presumably, 

 however, this infra-red band should only be exhibited by the 

 substance when in the opened up condition ; and as yet no 

 measurements have been made of infra-red absorption in this 

 direction. This also I hope to be able to carry out in the 

 near future. 



It would seem that a further experimental verification 

 might be sought in the refractivities of compounds which 

 Sellmeyer has shown can be connected with an absorption 

 band in the ultra-violet. Sellmeyer's formula in its simplest 

 form is 



1 N 



v^ — v- 



where N is a constant, v is the frequency of the ultra-violet 

 absorption band, and v the frequency of the light for which 

 a given value of the refractivity, /*— 1, is found. 



Phil. Mag. S. 6. Vol. 27. No. 160. April 1911. &2 U 



