Refraction and Dispersion of Gaseous Compounds. 599 



and for the interatomic 



, ,. -039018 xlO 27 r , 



(/*- 1 )Br 1 -:Br l = 713'4 X HF-n 2 ' * ' W 



( ... _ -0893xl0 27 ,,.-, 



^"" i ^-l 1 ~ 456xl0«-n*' * ' W 



It will be noticed that the three expressions on the right- 

 hand side of (1), (3), (4) form a series in which the numerators 

 increase regularly with increasing atomic weight, and the 

 denominators decrease. In this respect they resemble the 

 expressions for the ref ractivity of the three inert gases argon, 

 krypton, and xenon which I published two years ago* ; and, 

 if the numerators of the six expressions are compared together 

 by pairs, it is found that the numbers bear the same pro- 

 portion to each other. 



Comparison of the values of C in the expression 

 jjl — l = C/« 2 — n 2 for the halogens and inert gases. 



C'/C". Ratio. 

 Chlorine 3-8787 



Argon 4* 7 163 



& 



Bromine 4*3566 

 Krypton ~~ 5' 3446 

 Iodine 5' 1548 



Xenon ~ 6*1209 



- -822, 

 = -815, 

 = -842. 



Since the numerical values of the refractivities of each 

 triad are in the ratio of 2, 3, and 5 approximately, it follows 

 that the denominators of the same formulae, when compared 

 in the same manner by pairs, bear approximately the same 

 ratio. 



Comparison of the values of n 2 for the 

 halogens and inert gases. 



n' 2 /n" -. Eatio. 

 Chlorine _ 10558 

 Argon - 17009 ~ ' 



Bromine 8294 e 



= 12768 = ' 6a0 ' 



Krypton 



Iodine 6325 



= -705. 



Xenon 8978 



* Phil. Mag. January 1911, p. 69. 



