THE 

 LONDON, EDINBURQH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SEBIES.] 



SEPTEMBER 1881, 



XVIII. On the " Rotational Coefficient " in Nickel and Cobalt, 

 By E. H. Hall, Ph.D., late Assistant in Physics in the 

 Johns Hopkins University, Baltimore* . 



THIS article may be considered as the continuation of 

 one published in the ' Philosophical Magazine J for No- 

 vember 1880, under the title " On the new Action of Mag- 

 netism on a Permanent Electric Current," in which were given 

 the results of some quantitative investigations of a certain 

 phenomenon recently discovered in the Physical Laboratory 

 of the Johns Hopkins University. It will perhaps be remem- 

 bered that the essential feature of this phenomenon is the set- 

 ting up, in a conductor bearing an electric current, of an 

 electromotive force at right angles to the primary electromo- 

 tive force, when the said conductor is subjected to the action of 

 a magnetic force at right angles to the direction of the current. 

 In the article alluded to, results were given as obtained with 

 gold, silver, tin, platinum, iron, and nickel. The magnitude 

 of the effect observed, relatively to the strength of the primary 

 current, the intensity of the magnetic field, and the dimen- 

 sions of the conductor, had not been determined with any 

 accuracy in the case of nickel and tin, though it was known 

 to be comparatively large in nickel and small in tin. The 

 other metals ranged themselves, as regards the numerical 

 magnitude of the effect exhibited, in the following order, viz. 

 iron, silver, gold, platinum — the effect observed in iron being 



* Communicated by the Physical Society, having beeu read at the 

 Meeting on May 28, 1881. 



Phil, Mag. S. 5. Vol. 12. No. 74. Sept 1881. N 



