1915.] ADAMS— HALL AND CORBINO EFFECTS. 51 



His results are in good agreement with previous measurements 

 made with wires and strips. For example, in the case of bismuth, 

 using the same disk that was employed to measure the circular cur- 

 rent he found, for a field //=; 5,000, 8a/a = 0.16. Now c = 2X0"^ 

 for //= 5,000, so that c-//*^.oi. It is thus certain that some 

 other influence is efi^ective in causing the main part of the change of 

 resistance of a metal in a magnetic field ; it is very probable that the 

 field affects the molecular structure of the metal. 



The interpretation of these results from the point of view of 

 the electron theory of metallic conduction is unsatisfactory. I have 

 worked out their theory^ assuming free electrons in the metal that 

 collide with the metallic atoms and obtained very simple expres- 

 sions for the number of electrons in unit volume and their time 

 between collisions. The numbers so obtained are of the same order 

 of magnitude as have been obtained by other methods. But the 

 difficulty of accounting for the difference in sign of the effect for 

 different metals on any such simple theory indicates that if we are to 

 hold to the electron theory of metallic conduction other forces than 

 those resulting from collisions like those between hard elastic 

 spheres must be supposed to act upon the electrons. The surpris- 

 ing thing is that so much can be explained by the simple theory 

 of electrons when all such forces are neglected. 



We have seen that the Corbino effect is, essentially, the same as 

 the Hall effect. In its measurement and interpretation the Cor- 

 bino effect has some important advantages over the Hall eff'ect. In 

 the first place it is not necessary to use the very thin films that are 

 required to produce measurable Hall effects. And in the second 

 place the absence of the free transverse boundaries render the in- 

 terpretation of the Corbino effect simpler than that of the Hall 

 effect. 



Palmer Physical Laboratory, 

 Princeton University. 



3 Philosophical Magazine, XXVIL, p. 244, 1914. 



