Recent 
JUL. 
RADIATING PHENOMENA IN A STRONG MAGNETIC FIELD. PART IJ. —MAG- 
NETIC PERTURBATIONS OF THE SPECTRAL LINES. By THOMAS 
PRESTON, M.A., D.8c., F.RS. 
[ Read January 18, 1899. | 
In December, 1897, I laid before this Society an account of some experiments 
and observations which I had previously made while investigating the modifica- 
tions which the radiations from a source of light suffers when the source is placed 
in a strong magnetic field.* Briefly stated, the results then obtained showed 
that the majority of the spectral lines behaved according to the expectations of 
theory, and became resolved into triplets when viewed across the lines of force ; 
but, on the other hand, many lines deviated from this law, and became resolved 
into quartets, sextets, or other forms, under exactly the same conditions. 
In order to explain the existence of these deviations from the ordinary triplet 
type, it was suggested that they might be due to reversals in the cooler layers of 
vapour surrounding the source of light; but it was also pointed out that the 
appearance of these modified forms did not by any means favour that explana- 
tion, and, in addition, it was mentioned that deviations from the triplet type 
ought to be expected, for the conditions necessary to produce pure tripling 
could not be expected to hold good in all cases. 
It was consequently a matter of some importance to determine whether these 
more complex forms are really due to the action of the magnetic field on the 
vibrating ions, or to some extraneous cause, such as absorption. I accordingly 
tried sparking with weak solution, so as to diminish all chance of reversal, but in 
no case did the quartets or other modifications reduce to the triplet form. On the 
contrary, they became clearer and more precise as the lines became sharper with 
the reduced quantity of vapour. Nevertheless this was not regarded as seriously 
in opposition to the supposition of reversal, for the appearance of reversed lines 
in a strong magnetic field, where the spark is blown about, might differ from 
that of ordinary reversals. I then tried to further increase the strength of the 
* See Trans. R. D. S., vol. vi., p. 385, 1898. 
TRANS. ROY. DUB. SOC., N.S. VOL. VII., PART II, D 
