1)06 Effect of Mag iu tic Fields on Metallic Resistance. 



fields than 10,000. The behaviour of the Heusler alloy is of 

 special interest, being so much unlike that of the other metals, 

 and with the exception of the Kerr effect, this is the only 

 respect in which its magnetic properties are markedly different 

 from those of iron. 



Application of these results to the electron theory of 

 metallic conduction is rather unsatisfactory. On this theory 

 E. P. Adams * has derived an expression for the change of 

 resistance of a metal in a transverse field, 



rfR oT 1 e" TT2T2 



Here R is the resistance, T the free period of an electron, and 

 ST the change in the free period due to the molecular rear- 

 rangement produced by the magnetic field H. This equation 

 satisfactorily explains results. For a longitudinal field a 

 similar expression can be derived. Here the electron pursues 

 a spiral course about the lines of magnetic induction, so that 

 there is an increase of resistance resulting from the changed 

 motion. Corresponding to any change in the free period of 

 an electron the expression for the change of resistance may 

 be derived in the form 



R T" 



Here ST is of somewhat broader significance than in the pre- 

 ceding formula. It includes the change of free period due to 

 the altered path of the electron as well as the change due to 

 modified molecular structure. A longitudinal field should 

 thus produce a greater effect than a transverse field ; and this 

 is contrary to observed facts. By assuming that the molecular 

 rearrangement due to a transverse magnetic field produces a 

 greater increase of free period than that due to a longitudinal 

 field, the two equations above can be taken as expressing 

 experimental results. However, the effect of magnetization 

 on the molecular structure of a metal is of so complex a nature 

 and is so little understood that the equations probably tell 

 only a small part of the story. 



The experimental work was suggested by Professor E. P. 

 Adams, and his advice has been of the greatest help throughout 

 the experiments. 



Palmer Physical Laboratory, 

 Princeton University. 



* Phys. Rev. xxiv. p. 428 (1907), 



