ON RADIATION IN A MAGNETIC FIELD, 39 



Badiation in a Magnetic Field. — Report of the Committee, consisting of 

 the late Professor G. F. FitzGerald (Chairman), Professor W. E. 

 Thrift (Secretary), Professor A. Schuster, Principal 0. J. 

 Lodge, Professor S. P. Thompson, Dr. Gerald Molloy, and Dr. 

 "W. E. Adeney. 



The Committee have to refer with feelings of the deepest regret to the 

 death of their Chairman, Professor G. F. FitzGerald, and acknowledge 

 that their work has been much impaired by the loss they have sustained. 



That work seemed twofold : in the first place, to obtain specimen 

 prints and enlargements of the negatives left by Preston, in order to 

 consider the advisability of publishing them ; in the second place, to 

 study the negatives and measure the separations of the various lines. 



Nineteen of these negatives are interesting, viz., ten of iron, five of 

 cadmium and zinc, two of magnesium, one of strontium, and one of nickel, 

 but their value is much lessened because no information is obtainable 

 concerning the corresponding strength of the magnetic field. However, 

 from their examination of the specimen prints and enlargements which 

 they have obtained, the Committee conclude that it would be desirable 

 to publish prints of some, at least, of the negatives. They are interesting 

 on account of their priority as photographic records of the effect of a 

 magnetic field upon the spectral lines, and on account of the clearness with 

 whfch they exhibit the effect, both in its normal and in many anomalous 

 forms ; and the information derivable from them would thus become 

 a.vailable to all. The Committee, therefore, recommend their publication, 

 and ask for reappointment, with a grant of 15^., in order to carry this 

 recommendation into effect. 



The work of measuring the negatives has been confined to preliminary 

 investigations on the degree of accuracy attainable, and to some observa- 

 tions on the iron spectrum. With the instrument used by Sir Robert 

 Ball and Dr. Rambaut for measuring star photographs it was possible by 

 special arrangements to measure, in general, to 0'006 tenth metre. This 



\ 2 



would imply that the resulting values of -—, for example, 25-8 X 10^ are 



accurate to 0-2 or 0-3. But the calculated values of ~— for the lines, 



A\ 



observed so far, show such variety that the verification for iron of the 



law demonstrated by Preston for cadmium, zinc, and magnesium seems 



most improbable at present. 



Several anomalous lines have been observed, particularly the quintet 

 at 3743-51. 



No unaffected lines have been met with ; those which are not split 

 up into separate components are much broadened. 



Interference ami Polarisation of 'Electric Waves. 

 By Professor Dr. G. Quincke. 



[Ordered by the General Committee to be printed in extenso.'] 

 In the Physical Laboratory of the University of Heidelberg Dr. August 

 Becker has measured the wave-lengths of electric vibrations in inter- 

 ference-tubes with two bi-anches or in T-shaped tubes of the form which 

 Professor Quincke used for acoustical researches. 



The maxima and minima of the waves have been observed by means 



