Electrical Resistance of Bismuth to A Iternating Currents. 301 



the following qualitative ones : — If R r , R m , R<f, and R c are 

 the resistances of the bismuth to a rising, maximum, de- 

 creasing, and constant current respectively, then 



R y > R m > R e > R<f . 



More recently R. Wachsmuth and C. Bamberger * found 

 the resistance in strong fields to be quite independent of the 

 frequency. 



As these results are so mutually contradictory, Dr. Schuster 

 suggested that I should undertake a research on the subject ; 

 my aim being to find how the resistance of bismuth to alter- 

 nating currents depends on the frequency of the current if 

 the field is kept constant and large. 



In all my experiments a Hartmann and Braun bismuth 

 spiral (having a resistance of 17*88 ohms at 21° C. in zero 

 field) w r as placed perpendicular to the field produced by a 

 large electromagnet, the field-strength being about 17,000 

 lines per sq. cm., so that the resistance of the bismuth in the 

 field was double its value outside. The alternating current 

 used was generally obtained from a small dynamo which gave 

 a current curve approximately sinusoidal in shape. 



The method of experimenting was based on the following 

 considerations : — As any small change in the resistance of a 

 wire carrying a current may be considered as the result of 

 an E.M.F. set up in the wire, whatever the changes in the 

 bismuth may be due to they can be regarded as arising from 

 an electromotive force set up in the bismuth itself. If on 

 examination this E.M.F. (called in this paper the ''bismuth 

 E.M.F.") should prove to be opposite in phase to and of the 

 same wave-form as tbe — say simple harmonic — current 

 causing it, it may safely be inferred that the change in the 

 bismuth is really a change in the resistance pure and simple. 

 But if the " bismuth E M.F.," while still possessing the 

 proper wave-form, should be displaced 90° ahead or 90° 

 behind, it w r ould be necessary to conclude that in the one 

 case there exists something of the nature of capacity, in the 

 other something of the nature of self-induction in the bis- 

 muth. There is the further possibility of the " bismuth 

 E.M.F." having a different wave-form from that of the 



'to 



current. 



Two methods of experimenting were used. A direct 

 method of obtaining the wave-form of the. " bismuth E.M.F." 

 and of the current producing it will be fii^st described. 



* Physikalische Zeitschrift, I. ii. p. 127 (1899). 



