( 330 ) 
^ = <r“ f*+) = 
n,fto 2pv 
c 4 i? 2 -f 9' ’ 
(27) 
per unit of length. 
As for the case 0- = \ x, it will suffice to mention here that the 
two principal beams are rectilinearly polarized. For the one, whose 
vibrations are parallel to the lines of force, the maximum of absorp¬ 
tion, which occurs when n = n & , has an intensity determined by 
hi == 
c 9 
(28) 
For the other beam, whose vibrations are at right angles to the 
lines of force, the absorption for n = n 0 may be calculated by the 
formula 
hn = 
<«*•+*■) 
(29) 
$ 6. Let us now pass on to consider the propagation in a direction 
making an angle & with the lines of force. In doing so we shall, 
however, exclude cases in, which this angle is very near 0 or iar, 
because for these directions some terms which may in general be 
omitted, might become of influence *). 
When both sin and cos & are large in comparison with the 
small quantities occurring in our calculations, formula (12) may be 
replaced by 
! a — £i] sma* =0,. (30) 
so that 
(31) 
At the same time (14) becomes 
_ Xt 
w $ 
We have, therefore, when the quantities relating to the two principal 
beams are distinguished by the indices I and II, 
m m 
\PrJi\2>*)u ii Sii ' 
or, on account of (30), 
1} Notwi thstandmg this, we shall find that, if we put 3 =0 or 3 = \ we 
can deduce from some of our formulae results that are true for a propagation 
along the lines of force or at right angles to these lines. 
