MAGNETO-OPTIC PHENOMENA OF IRON, NICKEL, AND COBALT. 
101 
The values of n and k for iron, steel, and nickel will be found in a paper of Drude’s 
(‘Wied. Ann.,’ vol. 39, p. 481), quoted in Thomson’s ‘Recent Researches,’p. 421, 
The constants for cobalt are g’iven by Drude in ‘ Wied, Ann.,’ vol. 46, p. 407. These 
values are shewn in the following table :— 
Red light. 
Sodium light. 
nh. 
n. 
k. 
nh. 
n. 
h. 
Iron. 
3-20 
2-36 
l-3(i 
Steel. 
3-47 
2-62 
1-32 
3-40 
2 41 
1 -38 
Nickel. 
3-56 
1-89 
1-88 
3-32 
1 79 
l-8() 
Cobalt .... 
4T9 
2‘22 
1-89 
4-03 
2T2 
1-90 
wherein, for red light, \ = 630 X 10 centiin., and for sodium light we may take 
\ = 589'6 X 10“'^ centiin. 
Hence we find tlie corresponding values of R and «. 
Red 
light. 
Sodium liglit. 
R2. 
— a. 
R2. 
— a. 
Iron. 
15-86 
53° 40' 
Steel. 
I8-k 
.52° .51' 
16-87 
54° 4/ 
Nickel. 
16-20 
62° 0' 
14-29 
61° 44' 
Cobalt. 
22-48 
62" 7' 
20-72 
62° 14' 
The Kerr Experiments. 
14, We shall first compare our theory with the results of the Kerr experiments, 
which are so well known that they need not be here described. 
In Dr, Kerr’s second experiment the magnetisation is parallel to the reflecting 
surface, and to the plane of incidence ; and the incident light is polarised 
perpendicularly to the plane of incidence. Thus, in our notation, /3,-, = 0, yo — 
and Bq = 0 ; and the reflected light is specified by A and B, whose values as given 
by formula (36) are 
A = 
— (R"e^‘“ — M/m) (M + m) A^, 
(:RV‘“ + M/m) (M + m) 
— 2tcA (ci)~/Mm) Ai Aq 
'(RV 2‘“ + M/m)(M + m) 
1 
I 
}> 
I 
J 
B = 
(38). 
