Hackett — The Ionic Theories of Magneto-optic Rotation. 11 



_ I' 



A2 



We can evidently mite c-v = ^ {n-- 1) where ^ is of the same 

 order of magnitude as the highest values of - occurring in c-v. 



Writing = ord. as an abbreviation for ''is of the same order of 

 magnitude as" 



d = ord. — - . hi' - l)^ z. 



A- c T 



Expressing Verdet's constant in radians where A„, is its value in 

 minutes 



Am -, Stt^ n , „ n 



35^ = ora.---(«--l)-^^, 



■I£ 2A(m2 - 1) 3437-75 



Taking the value of Yerdet's constant for yellow line of sodium, 



we find that the average value of . , — - is about 1 x 10'- for the 



n{n' - 1) 



following substances : — methyl alcohol, ethyl alcohol, acetone, water, 

 benzene, carbon disulphide, quartz, rock-salt, sylvine, borax, selenium, 

 blende, fluorspar, diamond. 

 For these substances then 



4^ = ord. 1-6 X lO-^ 



which is of the same order as the values got in the more precise 

 calculation for carbon disulphide and creosote. Using this approxi- 

 mation to estimate the radius of the ionic orbits, we have 



J- = = lo-^ 



tJI 4 m. 

 r = ord. 1-8 X lO-\ 



