Electrical Resistance of Nickel in Magnetic Fields. 657 



rIYt 

 magnetization curve, we should expect the -p— curve to 



attain a maximum, and not to fall after reaching that maxi" 

 mum, a result which would possibly be obtained under ideal 

 experimental conditions, though it is not yet certain that the 

 fall is not a real effect. 



Adams * has investigated the matter theoretically for the 

 transverse field, developing the theory of J. J. Thomson, 

 but assuming the collisions between corpuscles and atoms to 

 be of the nature of those between hard elastic spheres.]! 



He obtains the expression 



BR _BT _i H ,^ 

 R ~ T 4 m 



rp 



where R is the resistance of the conductor with no magnetic 

 field, BR the change of resistance in a field of strength H, 

 T the time of free path, and BT the change which the mag- 

 netic field produces in the free period through alteration of 

 the molecular configuration. According to this theory, in 

 order that the transverse magnetic field may produce an 

 increase of resistance, it is necessary first thatBT be positive, 



BT e 2 



and secondly, that =- be greater than JH 2 — , T 2 . 



-L 9/1" 



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



