1075 
: 4 Rae B On 
with radii vectors that always have the same direction: — = + 0,627; 
rp 
this we call the motion D,. There is another mode of motion D,, 
in which the electrons describe straight lines and always have the 
same and equally directed deviations, but in which the frequency is 
inp, =+0,55 iw. To the value —0,55 dw belongs the direction of motion 
B NNT : : Ae 
— == 0,49, which is indicated in the figure and in which the deviations 
ry 
decrease exponentially; to +0,55 {w belongs one, in which the deviations 
increase exponentially; the lines of motion being equally but oppositely 
inclined with respect to the circle in the two cases. In the scond case 
core D, 
B | core 
= — 0,49. 
6 
re 
The system therefore is unstable, as has already been remarked 
by Bonr*) for all systems consisting of two nuclei with a ring of 
electrons between them. 
§ 3. In the vibrations A, C, and C, the molecule does not possess 
any resultant electric moment. Therefore an external electric force 
will never set the molecule in vibration, in this way and if the 
molecule had this motion, it would not exert an influence on the 
propagation. 
It is otherwise with the motions 5, D, and D,. In DeBie’s dispersion 
formula the second term corresponds to the motion B, the 1st and 
3 terms together correspond to the motion D,, the 4 and 5t together 
to the motion D,. This becomes evident by the following reasoning. 
The periodic electric force, which itself is proportional to cos (st-+-p), 
1) N. Bour, loc. cit. 
