Dispersion in Relation to the Electron Theory. 251 



those for benzene. The values of n are deduced from 

 Rubens' measurements. £ = 20° C. 



The absolute values are obtained from Perkins' water- 

 ratio for the D line (1-8957). 



Using equation (9) the values of \ l9 from sufficiently 

 separated values of X, are progressive. 



ac = *1571 

 bd = -1588 

 ce = -1614 

 #'=•1653 



ad =» -1534 

 be = '1613 

 cf = -1633 



The existence of at least two dispersional frequencies is 

 thus indicated. Proceeding to apply equation (10) we 

 obtain 



from ace, A 2 = '1819 



bdf, X 1 = -1886. 



The second value obtained from the larger values of 8 is 

 more probably free from the effect of experimental error. 

 Using this value, k x = 1*9916, k 2 = 1-2790. Thus 



10 



u X t = Vm*( jJ± £ m ) t +1-279. 



xxio 4 . 



$ (obs.). 



<p (calc). 



Diff. 



•6708 



3634 



3627 



-•007 



•589a 



3747 



3-751 



-f- 004 



•4958 



4-014 



4-002 



-•012 



•4529 



4194 



4-194 



•ooo 



•4046 



4-538 



4-530 



- -008 



•3631 



5014 



5-014 



•ooo 



From Simon's * values for the natural dispersion of 

 m. xylene in the ultraviolet I find 



a = -01444, a x = '56073, c = '00054, 



the mean effective value of Xi being '1830. Thus 



n 2 = 1-61444 + '56073 



X 2 



X 2 — -03349 



* Loc. cit. 



-•00054 X 2 . 



