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II. 



RADIATING PHENOMENA IN A STRONG MAGNETIC FIELD. PART II.— MAG- 

 NETIC PERTURBATIONS OF THE SPECTRAL LINES. By THOMAS 

 PRESTON, M.A., D. Sc, F.R.S. 



[Eead Januaut 18, 1899.] 



In December, 1897, I laid before this Society an account of some experiments 

 and observations whicli 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 trijjling 

 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. yi., p. 385, 1898. 



TEANS. Roy. DUB. SOC, N.S. VOL. VII., PART II. D 



