244 Prof. E. P. Adams on some Electromagnetic 



3. In the case of elements such as platinum, mercury, and 



lead there is a small amount of an " extra-radiation " 

 with an absorption coefficient of about 40 cm. -1 in 

 lead. This " extra-radiation " may be characteristic 

 of the radiator. 



4. The production of secondary y rays plays an important 



part in the absorption of the primary y rays. 



5. Lead produces more secondary y rays than does an 



equal mass of aluminium, zinc, or tin. 



6. The distribution of the secondary radiation Las been 



examined under various conditions. 



I wish to express my best thanks to Prof. Rutherford for 

 the supply of large quantities of emanation and for his advice 

 during the course of these experiments. 



XXYI. Some Electromagnetic Effects related to the Hall 



Effect. By E. P. Adams, Professor of Phy sirs, Princeton 

 University *. 



AX UMBER of interesting electromagnetic effects 

 were described by Professor Corbino two years ago 

 (Physikalische Zeitschrifi, xii. pp. 561, 842, 1911), which 

 have an important bearing on the electron theory of metallic 

 conduction. The theory of the experiments given bv him 

 does not lead directly to results which admit of numerical 

 calculation. He introduces both positive and negative carriers 

 of electricity, and his results involve the mobility of these 

 two kinds of ions. It is the purpose of this paper to develop 

 the theory of these effects in terms of the electrons and their 

 characteristics. While it is certain that the simple electron 

 theory of metallic conduction, involving collisions with the 

 atoms like those between hard elastic spheres, is very im- 

 perfect, it seems worth while to examine its consequences in 

 these cases. The results obtained are very simple and furnish 

 an excellent opportunity of testing the hypotheses involved. 



The three electromagnetic effects predicted and discovered 

 by Professor Corbino are the following : — 



(1) A metallic circular disk in which a uniform radial 

 electric current flows is placed in a magnetic field at right 

 angles to its plane. There results a circular current in the 

 plane of the disk such that the current density is inversely 

 proportional to the radius. 



(2) The disk with the radial current flowing in it is 



* Communicated by the Author. 



