118 
Proceedings of the Royal Society 
6. Laboratory Notes. By Professor Tait. 
(a) On a Possible Influence of Magnetism on the Absorption 
of Light, and some correlated subjects. 
Professor G. Forbes’ paper, read at a late meeting of the Society, 
and some remarks made upon it by Professor Clerk-Maxwell, have 
once more recalled to me an experiment which I tried for the first 
time rather more than twenty years ago, in Queen’s College, Belfast. 
I have since that time tried it again and again, whenever I suc- 
ceeded in getting improved diamagnetics, a more powerful field 
of magnetic force, or a more powerful spectroscope. Hitherto it 
has led to no result, but it cannot yet be said to have been fairly 
tried. I mention it now because I may thus possibly be enabled 
to get a medium thoroughly suitable for a proper trial. 
The idea is briefly this, — The explanation of Faraday’s rotation 
of the plane of polarization of light by a transparent diamagnetic 
requires, as shown by Thomson, molecular rotation of the lumini- 
ferous medium. The plane polarized ray is broken up, while in 
the medium, into its circularly-polarized components, one of which 
rotates with the ether so as to have its period accelerated, the other 
against it in a retarded period. Now, suppose the medium to ab- 
sorb one definite wave-length only, then — if the absorption is not 
interfered with by the magnetic action — the portion absorbed in 
one ray will be of a shorter, in the other of a longer, period than if 
there had been no magnetic force ; and thus, what was originally a 
single dark absorption line might become a double line, the com- 
ponents being less dark than the single one. 
Other allied forms of experiment connected with this subject 
were discussed. 
(6) On a Mechanism for Integrating the General Linear Differen- 
tial Equation of the Second Order. 
I am anxious to explain to the Society a kinematical device for 
the solution of the General Linear Differential Equation of the 
Second Order before I become acquainted with the principle of the 
integrating machine which, I understand, was described last Thurs- 
day by our President to the Boyal Society. 
