658 Electrical Resistance of Nickel in Magnetic Fields* 

 For the longitudinal field the expression 



3R__BT 

 R ~ T 



may be derived. It is pointed out by Heaps * that " here 

 BT is o£ somewhat broader significance than in the preceding 

 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." 



With reference to the difference between the effects for 

 the longitudinal and transverse fields respectively, it may, 

 however, be mentioned that for every specimen examined in 

 the present case the effect for the longitudinal field was 

 found to be markedly greater than that for the transverse 

 field. 



If, remembering the small magnitude of the current e.m.f., 

 we assume that the molecular rearrangements due to the 

 transverse and longitudinal fields respectively produce the 

 same maximum value of BT in each case, we may obtain 

 some idea of the order of magnitude of the free period of the 

 electron in nickel. 



Taking high values of the magnetic field in order to ensure 

 saturation, and identifying H in the above equations with 

 the magnetic induction B, we have from the above results 

 for the longitudinal position 



^ = *J = 23-47x10- 



where BT is the maximum change in T due to the longi- 

 tudiual field, BR the maximum change in R. 

 For the transverse position 



B = 17513; -~ =13-9 Xl0" 3 ; 



taking the demagnetizing factor as 2ir and the saturation 

 value of the intensity as 400. 



* Loc. tit. p. 906. 



