( 841 > 
by dd Bois in the case of iron, nickel, and cobalt, we may assert 
the proportionality between s and j with great probability. Bearing 
in mind this fact we are able to determine from purely magneto- 
optic measurements the order of magnitude or at least an inferior 
limit of maximum magnetization. As du Bois has shewn in the 
case of an unlimited homogeneous plane disc, the magnetization of 
which is uniform and normal, the abscissa of the point of intersection 
of the straight line e = Kj — if p/4?r and of the asymptote f = const 
has the value 4ar3 m . 
Accordingly 3m ^ 140 c .g.s. in the case of cupriferrite. The small 
inclination of the upper part of the curve in Fig. 3 may be explained 
by the fact that for irregularly formed specimens the real conditions 
do not correspond to those in the ideal case mentioned above. How¬ 
ever this inevitable difference can only produce a decrease in the 
apparent value of so that an inferior limiting value is really 
determined ; small fissures, cavities, and impurities in the reflecting 
surface are particularly capable of exerting such an influence. 
2. Magnetite . The dispersion of the KERK-Effect is shown in Table 3 
and Fig. 4 (continuous line). If we compare this curve with the 
TABLE 3. 
+ 24.9 
+ 21.0 
+ 3.32' 
+ 2.5O' 
± (MB'=0.9% 
i 0.05'= t.5 
±0.03'= 2 
± 0.02'= 0.6 
± 0.02'= 0.5 
±0.02'= 0.4 
± 0.02'= 0.5 
±0.04'= 1 
± 0.07'= 3 
>) H. „u Bois, Wied. Am. 31 p. 966, 1887; PUL Mag. (5) 29 p. 301, 
