﻿488 Mr. J. B. Henderson on the Effects of Magnetic 



advantage which this method possesses over the usual one in 

 the case of a new system is that, in making it up, we have 

 only unmagnetized needles to handle ; an advantage which 

 those who have had much to do with this kind of work can 

 readily appreciate. 



Astro-Physical Observatory, 

 Washington, D.C., February 1893. 



LVIII. On the Effects of Magnetic Fields on the Electric 

 Conductivity of Bismuth. By James B. Hendekson, B.Sc* 



[Plates XV. & XVI.] 



^ j^HAT magnetic fields have an effect on the electric con- 

 -*- duetivity of metals was noticed first in the year 1856 by 

 William Thomson f (Lord Kelvin), who was led to suspect it 

 from the effects which he had discovered magnetization to have 

 on the thermoelectric properties of metals. He experimented 

 on iron and nickel, and found in both an increase of resist- 

 ance along the lines of force, and a diminution perpendicular 

 to them. 



Bismuth was first experimented on by TomlinsonJ, who 

 found an increase of resistance due to longitudinal magneti- 

 zation of Bi wire, and he found a similar increase in Fe, Ni, 

 Co, and steel wires. Later investigations in this subject have 

 been made by Righi§, Hurion ||, LeducIF, Ettingshausen and 

 Nernst**, Ettingshausen ft, GroldhammerJt, Lennard and 

 Howard §§, and Lennard || || ; but the last of these is the one 

 which has the most important bearing on the present in- 

 vestigation. 



In this Lennard used spirals of Bi wire, in all fifteen 

 spirals being tested, whose wires varied from 0*2 to 0'4 

 millim. in diameter, and from 50 to 150 centim. in length, 

 the respective resistances varying from 6 to 25 Siemens 

 units. The resistance was determined by the Wheatstone- 

 bridge direct-current method, and also by the method using 



* Communicated by the Author. 



t Math, and Phys. Papers, ii. p. 307. 



% Phil. Trans. 1883. 



§ Journ. de Physik. iii. p. 355 (1884). 



|| Compt. Rend, xcviii. p. 1257 (1884). 



5[ Compt. Rend, xcviii. p. 673 (1884). 

 ** Wien. Ber. xciv. part ii. p. 560 (1886). 

 t+ Wien. Ber. xcv. p. 714 (1887). 

 XX Wied. Ann. xxxi. p. 360 (1887) ; xxxvi. p. 804. 

 §§ Electro -technische Zeitschrift, ix. p. 341. 

 - || |i Wied. Ann. xxxix. p. 619 (1890). 



