Dispersion in Relation to the Electron Theory. 463 



very closely with that obtained by Rubens from natural 

 dispersion, namely, 



\ 1 =-103/a. 



Hence we may conclude that only one value of rj occurs 

 here. For this substance Rubens gives a 1 \ 1 2 = "010654. 

 Substituting these values in equation (12), and taking 

 £ = •01664' for X= '5893, I find 



7? — = 1'37 x 10 7 e.m.u. 

 m 



If the values of the effective e/m thus determined are 

 used in place of the normal value for calculating the value 

 of p from the natural dispersion (Table II.), we obtain *: — 



Quartz j9 = 5"l, Sylvine p=2'4, 



Fluorite p=5'l, Rock-salt ... p = 4*2. 



For other substances the value of a is not known with 

 the same degree of certainty, since the determinations of n 

 have not been made with sufficient accuracy over a large 

 range of the spectrum. Taking the values at present ob- 

 tained, the results for several liquids are given below, 

 equation (10) being used. 



Table V. 



Substance. 



P- 



1 



3-250 



2-305 



1-896 



3-826 



d. 



n j>- 



a . 



P- 



Water 



1 

 1-263 



•879 



•878 



1-487 



1-333 



1-6307 



1-5005 



1-4950 



1-65S2 



•268 

 •634 

 •557 

 •614 

 •954 



1-4 

 4-9 

 5-1 

 6-7 



5-7 



Carbon-bisulphide 



Benzene 





Naphthalene bromide 



It will be noticed that the values of p in comparison 

 with v are always much smaller in unsaturated compounds 

 than in others. This is in all probability due to the existence 

 of a long dispersional period widely separated from the 

 next shorter period. 



The calculation of p from the formula for magnetic 

 rotation alone could be made if the constants were known. 

 From the formulas obtained in Part I. for some of the above 



* See Note 2. 



