front of a circle whose plane is at right angles to the lines of force. 
If we imagine a point moving along this circle in the direction in 
which the equivalent electron moves in the mode of motion x 2 +, 
the projection of this motion on the wave-front indicates the direction 
in which the characteristic ellipse is described. 
All this agrees with the elementary theory of the ZEEMAN-effect 
and similar remarks apply to the other outer component of the triplet. 
§ 7. We shall now enter upon some more details concerning the 
.propagation of rays whose frequency n 0 corresponds to the middle 
point of the triplet. In order not to exclude cases in which the 
components of the triplet are not neatly separated or hardly so, we 
shall not assume that v is much greater than g. 
For n = n 0 we may use the values (24) and (25), whereas 
'»!=-—S.(33) 
9 
Hence, if we abbreviate by putting 
.• • • < S4 > 
we find from (31) and (32) 
= V\-f , . ... (35) 
and 
s — — 1 — 2. 
4v s -j- <7 2 
In discussing these results we shall suppose the quantities v and q, 
which are related to each other in the manner shown by (34), to 
be positive * *). 
The nature of the phenomena that will be observed greatly depends 
on whether q is greater or less than 1. Both cases may occur. Indeed, 
if we determine an angle ^ by the equation 
(37) 
as we can always do, whatever be the value of -, we shall have 
or <1, according as > or <^^ 1 . ^ 
nft .L e .^ antlt y v 1S positive when the magnetic field has the direction of the 
* (S ° lhat the Action of the rays makes a sharp angle with the 
comnon When ’ besides ' the ^ and left-handed circularly polarized 
relative do<?V 6 fP ectral lme m the longitudinal Z EEM AN-effect have the ordinary 
noiifion P H T S - The Slgn ° f V is Chan ^ botb b y « Aversion of this relative 
position and by an inversion of the field. 
