MAGNETO-OPTIC PHENOMENA OF IRON, NICKEL, AND COBALT. 
97 
In the metal, 
V = L. + — I ^ Aoe‘+ 
nij ^ 
_"i" Wli~ + pO (^-' 
?«1 ‘ »i2 ^ 
(29). 
In this assumption we take account of only two of the four possible waves in the 
metallic medium ; the other two are omitted because they are waves which travel in 
a direction that makes an acute angle with the axis of 2 ; and as in our present 
problem all waves in the metallic medium are originated at the plane z = 0, only 
those can actually occur whose direction of propagation makes an obtuse angle with 
the axis of z. 
10. The surface conditions which have to be satisfied are the continuity of 
P, Q, w 
a, b, c 
across the interface; and, as usual, the continuity of Q involves that of c, while the 
continuity of b involves that of lu. 
Thus the conditions are four, namely continuity of 
(1) w 
(2) P, which = H p 
(3) 'Q, which = H (u — 
(4) a, which leads to the continuity of dQjdz or d/dz.H (v 
We shall denote the H of the metallic medium by H' to distinguish it from that 
of air. In the air H = — If r be the periodic time, and. X the wave¬ 
length in air of the light considered, 
p — — 27rc/X, 
so that 
H = — 2icX. 
)> (30). 
I 
— IIi7P(; + Hi73m) j 
Also since t, and therefore p, is the same for the metal as for the air, we see by 
(20) that 
= — 4lttlp — d 
and therefore >.(31)> 
H/H' = ^ i)2g2.a J 
VOL. CXG.—A. 
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