McKAY. — HALL EFFECT AND CURRENT DENSITY IN GOLD. 855 



E 

 The expression -^ is here seen to be practically constant over the 



range used. 



Moreau * made a series of measurements in very thin silver and nickel 

 plates. These metals were deposited on glass plates. The following 

 results were obtained with a silver plate, in which the main current was 

 varied while the magnetic field was kept constant : 



1.81 



1.80 



182 



1.78 



1.79 



1.76 



1.80 



1.76 



E is the thickness of the plate in millionths of a millimeter ; / is the 

 strength of the primary current in milliamperes ; Ai is the deviation of 



Figure 1. 



the galvanometer in the secondary circuit ; H is the strength of the 

 magnetic field. 



The greatest range of primary current seems to have been obtained by 

 IMoretto.f The only metals which he mentions in his paper as having 



* Journal de Physique, Serie 3, 10, 478-493 (1901). 

 t Nuovo Uimento, Serie 4, 11, 278-289. 



* Moreau also investigated the influence of tiie thickness of tlie metal plate. He 

 found that when the thickness of the plate was reduced below 44 ^uyu the Hall effect 

 was less than the value calculated from measurements of thick phites. 



It has been observed by various experimenters tliat the Hall effect in gold leaf is 

 less than that of thick gold. 



