( 338 ) 
is only by 1 their velocities of propagation, bnt not. by the intensity 
of the absorption, that the two beams are different. 
We can diminish ^ by making v greater. Hence, the region of 
the transverse effect expands when the magnetic field is strengthened, 
and finally, when - has become v6ry large, i. e. when the distance 
between the magnetic components far surpasses their breadth, the 
longitudinal effect is confined to a very narrow interval. 
We may add that any definite direction of propagation may be 
made to fall within the limits of the transverse effect by properly 
strengthening the field. At the same time, the phenomena become 
more and more like those that are observed at right angles to the 
lines of force. Indeed, when v is made greater, q increases continually, 
as may be seen from (34). The angle X/ whose value is given by 
(39), tends towards the limit 0, so that finally the two principal 
directions of vibration will be perpendicular to each other, the second 
of them being also normal to the field. Formula (41) shows that, at 
the limit, the index of absorption of the second beam becomes 0, 
and equation (40) may be replaced by 
or, if we take into account the formula (34) and fact that v becomes 
very much greater than g, by 
(cf. formula (28)). These conclusions may be compared with well 
known results obtained in the elementary theory of the ZEEMAN-effect 
in the radiated light, namely that the direction of vibration lies in 
the plane passing through the ray and a line of force, and that the 
amplitude is proportional to sin 
$ 11. From a theoretical point of view it is interesting to examine 
somewhat more closely the special case in which the rays have the 
direction determined by the angle & 1 . Our formulae would lead us 
to infer that in I his case the two principal beams are polarized in 
the same way, so that after all there would be only one kind of 
vibration that can be propagated. Of course this cannot be true. 
The difficulty can be overcome by pushing our approximations a 
step farther than has been done in the preceding calculations, in 
which we have omitted all quantities that are of an order higher 
than the first with respect to u\, w 2 +, u 2 —. 
