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LXXIII. The Change of Resistance of Metals in a Magnetic 

 Field at Different Temperatures. By S. C. Laws, M.A., 

 B.Sc* 



EXPERIMENTS on the change of resistance of metals 

 in a magnetic field have been made by Patterson f, 

 Grumnach if and others. These observers have found that 

 all metals show a change of resistance in the magnetic field, 

 all except the magnetic metals showing an increase of 

 resistance in all fields ; except for Bismuth, however, this 

 increase is very small, being usually less than yj th of 1 per 

 cent, for a field of 10,000 c.G.s. units. 



Fleming and Dewar §, working at temperatures varying 

 from 19° to — 203° 0. have made measurements on the change 

 of resistance of Bismuth, and have found a very considerable 

 increase at low temperatures ; while Righi || has made similar 

 experiments at temperatures ranging from 19° to 108° C. with 

 similar results. 



From the point of view of the electron theory as at present 

 understood, a change of this nature is to be expected if a 

 lowering of temperature produces an increase in the moan 

 free path of the corpuscle. This change is required from 

 considerations of the thermoelectric effect and the change 

 of resistance with temperature. 



The experiments described in this paper were undertaken 

 in order to get some further evidence on this point. Cadmium 

 and Zinc were selected as suitable metals for the experiments, 

 since in these the effect to be measured is larger than in any 

 others among those examined by Patterson or Grumnach. 



Experiments have also been made with pure graphite, this 

 substance being interesting theoretically from the fact of its 

 negative coefficient of increase of resistance. 



It has also been found to show a comparatively large change 

 of resistance in the magnetic field. 



The apparatus with which experiments were made con- 

 sisted of a Wheatstone bridge arrangement in which the 

 metal under examination formed one of the four arms of 

 the bridge. The adjacent arm consisted of two sets of 

 standard resistances arranged in parallel, one of these, Y, 

 serving to provide a first approximate balance, the second, X, 

 which was of higher resistance — 1000 to 2000 ohms — serving 



* Communicated by Sir J. J. Thomson, F.R.S. 



t Patterson, Phil. Mag., June 1902. 



X Grumnach, Ann. der Phys. xxii. 1, 1907. 



§ Fleming and Dewar, Proc. Roy. Soc. lx., 1897. 



|| Righi, Atti della R. Accad dei Lincei, xix., June 1884. 



