﻿Fields on the Electric Conductivity of Bismuth. 489 



alternating current and telephone, and a remarkable difference 



was found in the resistances obtained by the different methods. 

 Two kinds of Bi were used, one chemically pure and the 

 other containing traces of Fe and Zn, but differences were 

 not more than those due to observational errors. Deviations 

 from the mean values amounted to 1 per cent. The tem- 

 perature varied from 10° to 25° C, and once was 0° C. 



The present investigation was instituted to determine de- 

 finitely the relation between the magnetic field and the 

 resistance of Bi wire going to much higher field-intensities 

 than had e\er been experimented with, and also to determine 

 the influence of temperature on that relation if any was 

 found. The investigation was started purely from the scien- 

 tific standpoint, but the importance of it to the practical 

 application of Bi wire as a field-tester was not lost sight of. 



Owing to the purity with which Bi wire is now prepared 

 for instruments for magnetic-field testing, and the convenient 

 form for experimenting which these field-testers offer, it was 

 detsrmined to use them in this investigation. Two such were 

 employed, the spiral of one having a diameter of about 

 18 millim. and a resistance of 24 ohms, and that of the other 

 a diameter of 6 millim. and a resistance of about 9 ohms. The 

 form of the instrument is shown in fig. 1. 



Fig.l. 



The magnetic fields were obtained by means of a Euhm- 

 korff electromagnet, and the very highest field-intensities 

 from the large ring-electromagnet lately designed by H. du 

 Bois* for the production of very strong fields for experi- 

 mental purposes. With the large spiral the ordinary dome- 

 shaped pole-pieces belonging to the Ruhmkorff magnet were 

 used, the holes in them being first blocked up with pieces of 

 soft iron to render the field as uniform as possible. For the 

 small spiral special pole-pieces were prepared, which were 

 designed to fit the ring-electromagnet, but by using a pair 

 of flat poles with them they also fitted the Ruhmkorff 

 magnet. They had an angle of 60°, and their faces, which were 

 7 millim. in diameter, were held at a distance of 1*5 millim. 

 apart by means of a brass casting to which both pole-pieces 

 were rigidly attached. This casting consisted of two thick 

 rings held rigidly parallel and coaxial by means of two stout 



* Maynetische Kreise, p. 277 j Wied. Ann. li. (1894) ; Phil. Mag. May 

 1894. 



Phil. Miuj. 8. 5. Vol. 38. No. 234. Nov, 1894. 2 L 



