MAGNETO-OPTIC PHENOMENA OF IRON, NICKEL, AND COBALT. 115 
The experimental results used in the following’ table are taken from a paper by 
Dr. C. H. Wind (‘ Communications from the Leiden Laboratory of Physics,’ No. 9);— 
Polar Reflection from Nickel. Yellow Light. 
Angle 
of incidence. 
Strength 
of magnetic field in 
C.G.S. units. 
Calculated value of 
h - X. 
Observed value of 
Vli. 
■d; + uii — r. 
,39° 4' 
2190 
21 r 43' 
14° 32' 
287° 15' 
55° 
9560 
266° 7' 
17° 47' 
283° 54' 
75° 
12470 
249° 28' 
32° 25' 
281° 53' 
For incidence of 39° 4' Zeeman’s result is to be preferred to that of Wind, as he 
took more precautions to eliminate causes of error. For the other two angles of 
incidence agreement is indicated if x is about 77°. 
In estimating the consistency of the above results it is to be remembered that the 
optic constants (R and a) for different sjiecimens of nickel are often sensibly different. 
(I have used the same set of values all through.) Itideed in the case of iron Zeeman 
found that his obsei’vations of the optic constants of a particular mirror, made respec¬ 
tively before and after an observation of the Kerr phenomena, differed considerably. 
Cohalt. 
27. In his paper in the ‘Archives Neerlandaises,’ vol. 27, Zeeman describes 
experiments made by himself on mirrors of cobalt, and also quotes the results of 
experiments made by Drude. The comparison of these with the present theory is 
shewn in the following tables :— 
Polar Reflection from Cobalt. White Light. 
Angle of 
incidence. 
Calculated value of 
180°. 
Zeeman’s observed 
value of 
m — 180°. 
m — X — 360°. 
45° 
272° ir 
20° 34' 
-67° 15' 
60° 
265° 34' 
27° 40' 
-66° 46' 
73° 
255° 6' 
37° 55' 
-66° 59' 
Good agreement is indicated if x = 67°. 
Q 2 
