( 331 ) 
This means that one of the characteristic ellipses can be considered 
as the reflected image of the other with respect to a line bisecting 
the angle X'OY, a rule which also applies to the direction of motion 
in the two cases. 
The imaginary parts of u u « 2+ , on which the absorption 
ultimately depends, have their maximum values for n = »i> n 2 +, n 2 -, 
and have diminished to a small part only of the maximum value, 
when \n —»,|, |n—« 2 +| or |»—n*-| is equal to a moderate multiple 
of the coefficient g. 
From this we can infer that, when v is sufficiently great in com¬ 
parison with g , there will be three maxima of absorption at the 
points' of the spectrum determined by (16), and that, if v greatly 
surpasses g , we have three absorption bands that are completely 
separated, the body being practically transparent to rays of the 
interlying wave-lengths. At a point where the imaginary part of one 
of the quantities u u u 2 +, u 2 - has its maximum value, both the 
real and the imaginary parts of the two other quantities may, under 
these circumstances, be neglected in comparison with that maximum 
value. For n — for instance, we may put 
by which the roots of equation (30) become 
£ = — ri cos* # and £ — 12- 
Choosing the first root, we find 
_ i__ 
2V cos#’ 
( ri=*| i -TV (1+o H’ 
and if we take the second 
00 = fV 
It appears from these results that only the first of the two principal 
rays is absorbed, and that the axes of its characteristic ellipse are 
parallel to OY and OX', being to each other in the ratio of 1 to 
cos this ellipse can be considered as the projection on the wave- 
