Magnetic Field on Metallic Resistance. 737 



1 

 its approximate value 3— *we find that "p " is of the order 



v N 



10 23 . This is exceedingly large and indicates an internal 

 radioactivity far greater than any external radioactivity of 

 which we have experience. It is quite possible, however, 

 that the ease with which corpuscles pass from one atom to 

 another in close proximity to it, is incomparably greater than 

 the ease with which a corpuscle leaves an atom and flies into 

 space. If such a transference of corpuscles actually does 

 take place it is conceivable that there-arrangement of atoms, 

 which undoubtedly results upon the creation of a magnetic 

 field, may cause a great diminution in the number of cor- 

 puscles which are so transferred. Moreover, after a certain 

 field value the internal re-arrangement ceases and one would 

 therefore expect to find a maximum value for the resistance 

 effect. 



All metals show a slight resistance change in a magnetic 

 field but those which are very susceptible to magnetic influ- 

 ence show far greater effects than others, i. e. those metals 

 whose internal structures are easily altered show the greatest 

 resistance change. Such a diminution in transference of 

 corpuscles as has been suggested would result in increased 

 resistance whether the nickel were placed in the field trans- 

 versely or longitudinally. This actually is the case as the 

 diminution observed in large transverse fields is due to 

 another factor. If the change were due to an alteration of 

 mean free path, then the two effects would be of opposite 

 signs, as the length of the wire is diminished in longitudinal 

 fields and increased in transverse ones. We may therefore 

 conclude that a magnetic field causes a re-arrangement of 

 the atoms which results in a dimensional change and a 

 diminution of " internal " radioactivity. To this latter factor 

 the resistance change is due. As the dimensional change 

 and the resistance change are both due to the atomic re- 

 arrangement we should naturally expect to find a similarity 

 between the two effects; figure 12 shows that such similarity 

 exists. 



The Transverse Effect. 



The second part of the transverse effect has a different 

 origin from the first and has no analogue in the longitudinal 

 effect. Thomson * deduced theoretically that an effect pro- 

 proportional to H 2 was to be expected in a transverse field r 



* Internationale Congres de Paris, 1900. 



