MR. J. a. LRATHEM ON THE THEORY OF THE 
If the incident ray be as represented in the figure, and i he the angle of incidence, 
and p and w be positive, then 
I = — 0 ) sin i 
m = o) cos i. 
The incident ray being plane polarised, is real. 
But A and B are both complex, and have not 
necessarily tlie same vector angle ; hence the 
reflected light is elliptically polarised. If 6 be the 
angle through which the major axis of the ellipse of 
polarisation is rotated round the reflected ray (in the 
direction from the axis of x towards the axis of y) 
from the plane x = 0, since the modulus of B is very 
small compared with the modulus of A, 6 is given by 
B = real part of (B cos i/A.) 
in circular measure. 
In the case of iron, Kerr found that when is negative, B is negative if i be 
less than about 75°; while if i be greater than 75°, B is positive. The angle of 
incidence for which B changes sig’n (and therefore vanishes) has been observed bv 
different experimenters, whose results differ considerably. They are as follows :— 
Now from (38) 
so that 
I! cos i 
A 
where 
and, therefore, since 
Kerr 75°. 
Kundt 80° to 82°. 
Bighi 78° 54'. 
SiSSINGH 80°. 
Drude 79°. 
o 
~ (];A2‘“ - M/«0 (M + m) 
2cX sin i cos i 
' + cosr)(iWR-b'-2‘“-cos0 
i« = M/w, 
a,2RV“ = D? = M* + sill* i 
sin*? 
(38*), 
(39). 
