110 Dr. L. Silberstein on Molecular 



have selective absorption. The same is the case when y 

 (which is independent of H) is approached, for then co 

 itself, and therefore the first term in (24 a) becomes infi- 

 nite. This singular role of 7 and y' is shown explicitly 

 in (25 a), which is but another form of (24 a). 



For the numerical application of our formulae to the 

 molecular and the atomic refractivities as usually defined, 

 it will be well to write at least the last two ones in terms of 

 N instead of ay. Remember that, by definition, 



al]Sr=3d/M=fflm K : 1-008, 



where m-g_ is the absolute mass of a hydrogen atom, 

 164.10- 24 gr., so that 



and similarly, 



where a is the constant 



3ra H 



1-008 

 Thus (24 a) becomes 



10" 24 gr. . . . (27) 



and (25 a) 



N -3 No+ 3-l-2aN /RS' • • * < 246 ) 



N = 2B/_2_ + _ T i\] 



3«\y -7 7-7/' L ... (25 6) 

 7 '=7o-2B/R 3 . J 



Finally, we have for the singular distance, as a function 

 of the incident frequency Vy, 



&=(2cKJW, (26 a) 



where JV is a known function of y, viz. J3/a(yo—y). It will 

 be remembered that B stands for the constant e 2 /m. 



4. Formula? for Diatomic Substances discussed and 

 illustrated. 



Before passing on to the considerably more complicated 

 case of triatomic molecules, it will be well to discuss some- 

 what further the refraction formulae obtained in the last 

 Section and, possibly, to make in this connexion some 



