76 Proceedings of the Royal Society of Edinburgh. [Sess. 
fewer than 17 to 19 components, the largest numbers hitherto found — 
Professors Voigt and Lorentz made use in their theories of couplings between 
electrons of the same vibration frequencies. The latest step taken by 
Professor Voigt as a result of these newest observations on dissymmetry 
is to introduce couplings between two electrons of different vibration 
frequencies. The theory shows that cases of normal and abnormal dissym- 
metrical triplets arise, that the intensities of the two outer components are 
the same, and that the displacement of the lines which produces the 
dissymmetry is proportional to the square of the magnetic field strength 
used. All these conclusions may be compared with the results arrived at 
for the uncoupled electrons. Thus the subject of the dissymmetry of the 
components is important, as it may lead to a more accurate knowledge of 
the grouping of the electrons and the constitution of the atom. While 
Professor Voigt’s book was being printed, observations appeared by P. 
Gmelin * showing that in the case of the dissymmetrical triplet, A — 5790,f 
of the mercury spectrum, the displacement of the middle line was propor- 
tional to the square of the field strength. 
In the following my observations are given, and an attempt is made to 
show that in addition to the possibility of the presence of such couplings 
in some cases, as Professor Voigt has assumed, there is evidently some con- 
nection between the rotation of the plane of polarisation produced by the 
concave grating apparatus used and the dissymmetry observed in many of 
the cases. There are, however, also examples of dissymmetry which are 
exceptions to such a rule ; and further, there are symmetrical separations 
which seem to be wholly uninfluenced by the rotation of the plane of 
polarisation. 
With the concave grating apparatus of the Physical Institute, University 
of Gottingen, photographs of the transversal Zeeman Effect were in the first 
place taken, i.e. the light at right angles to the magnetic lines of force was 
used, and hence in the case of triplets all three components were present. 
From these photographs both the type and the amount of the dissymmetry 
were observed, but one could decide nothing about the displacement of the 
components which had caused the dissymmetry. The variation in the 
separations of the components is very striking, the difference between the 
separations towards red and violet amounting in some cases to over 25 per 
cent. 
The grating apparatus in that laboratory has already been described.^ 
* P. Gmelin, Phys. Zeit ., ix. 212, 1908. 
t All wave-lengths will be given in angstroms. 
% Phys. Zeit., vi. 25, 1905. 
