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VI. — Experiments on the Transverse Effect and on some Related Actions in Bismuth. 



By J. C. Beattie. (With a Plate.) 



(Read 17th December 1894.) 



Section I. — Introduction. 



Clerk Maxwell, in his Electricity and Magnetism, vol. i. § 304, makes the 

 following remark about the rotatory coefficient : — " It should be found, if anywhere, in 

 magnets which have a polarisation in one direction, probably due to a rotational 

 phenomenon in the substance." 



The current which should arise from such a coefficient was first observed by 

 Hall. He passed a current through a strip of metal ; he then found two points on 

 opposite sides of the strip, which, while the current was flowing, were at the same 

 potential, and which therefore indicated no current when joined to a galvanometer. 

 The plate was next brought into a uniform magnetic field, and when everything was 

 steady the two points previously at the same potential were no longer so, and a current 

 flowed through the galvanometer. This effect is observable in all conductors. 



Kundt * has shown that in iron, nickel, cobalt, it is proportional to the magnetisation. 

 Whether this is true for the diamagnetic metals has not, so far as I know, been definitely 

 settled yet. But, should this be proved, we have a comparatively easy method for 

 studying the magnetisation in these metals. 



Another phenomenon which may advantageously be studied by means of the trans- 

 verse effect is the variation of resistance of conductors carrying a current in a magnetic 

 field. Goldhammer t has shown in another way that the increase or decrease of the 

 resistance in bismuth is proportional to the square of the magnetisation, and suggests 

 that the same may be true for cobalt and nickel. Evidently the proportionality or non- 

 proportionality for these two latter metals can be settled at once by comparing the 

 variation of resistance and the transverse effect at the same field strength ; and, 

 similarly, the same method can be employed to show whether or not the variation of 

 resistance bears any relation to the magnetisation in all cases where it has first been 

 proved that the magnetisation and the transverse effect are proportional. So far as I 

 know, this method has not as yet been tried experimentally. I propose in another paper 

 to give some results relating to this matter. 



In bismuth the transverse effect has not yet been proved to be proportional to the 

 magnetisation ; nor, indeed, is it certain that the so-called transverse effect in bismuth is 

 a pure Hall effect, \ or is caused by a number of separate effects. As I shall show later, 

 the transverse effect in most cases is really the sum of three effects. 



* Wiedemann's Annalen, 1893, Bd. 49, S. 257. t Wiedemann's Armalen, 1889, Bd. 36. 



\ By Hall effect is meant a transverse effect proportional to the first power of the magnetisation. See " On Rela- 

 tion between the Variation of Resistance in Bismuth, &c," Trans. R.S.E., vol. xxxviii. 



VOL. XXXVIII. PART I. (NO. 6). 2 H 



