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XXVII. On the Electrical Resistance of Bismuth to Alternating 

 Currents in a Strong Magnetic Field. By Geokge C. 

 Simpson, B.Sc, Scholar of the Victoria University*. 



OXE of the many anomalous properties of bismuth is the 

 change which the resistance of a filament undergoes 

 Avhen placed perpendicuLir to the lines of force in a strong 

 magnetic field ; not only does its resistance very much 

 increase, but, as discovered by Lenard, its resistance to alter- 

 nating currents under these conditions is apparently different 

 from its resistance to direct currents. Many experimenters 

 have studied this difference, and although nearly all are agreed 

 as to the way in which it varies with the strength of the field 

 — the frequency remaining constant — each experimenter seems 

 to have arrived at a different conclusion as to the way it varies 

 with the frequency — the field remaining constant. 



Lenard f (who measured the resistance of the bismuth by 

 means of a Wheatstone-bridge, using an induction-coil to 

 supply the alternating current, and a telephone in place of 

 the galvanometer) concluded that the resistance of bismuth 

 in a strong field is the same for alternating as for direct 

 currents until frequencies of the order of magnitude of 

 10,000 per sec. are used. 



On the other hand M. Sadovsky J, working at St. Peters- 

 burg, showed that with the bismuth in a strong field, an 

 alternating current having a frequency of three or four 

 alternations per second produced a change in the resistance 

 of the bismuth. 



In M. Sadovsky's apparatus an alternating current from a 

 dynamo was supplied to a Wheatstone-bridge containing the 

 bismuth. On the shaft of the dynamo three segments of 

 brass, each extending over 60° of the circumference, were 

 fixed. By pressing a spring into contact with the first 

 segment, the galvanometer-arm was closed for J of an alter- 

 nation ; on pressing another spring, the galvanometer arm 

 was closed for the next £ ; and a third spring closed it for 

 the next ^ of an alternation. In this way the galvanometer 

 was connected to the bridge, 1st, when the current was rising 

 in the bismuth; 2nd, when it was at the crest of a wave 

 (current maximum) ; 3rd, when it was decreasing. M. Sa- 

 dovsky did not aim at quantitative results, but he obtained 



* Communicated by Prof. A. Schuster, F.R.S. 

 t "Wied. Ann. xxxix. p. 619 (1890). 



X Journal de la Societe Physico-Chimique Husse, vol. xxvi. no. 2 

 (1894). 



