McKAY. — HALL EFFECT AND CURRENT DENSITY IN GOLD. 373 



The larger absolute values of the Hall effect obtained here may have 

 been due to a smaller air-gap between the magnet poles than in the 

 preceding measurements. The strength of the magnetic field was 

 measured before this last set, but not, as had been previously the cus- 

 tom, after it also. As the wedging, intended to keep a constant width 

 of the gap, was generally changed during the removal of the plate from 

 the gap, some differences between the sets of measurements might be 

 expected from this cause. In the case of all measurements later than 

 May 7 the wedging was left unchanged by the experimenter during a 

 set of consecutive measurements involving changes from weak to strong 

 main current or vice versa. 



The following table gives the values of the current density used in 

 each set of observations on each plate, and the corresponding values of 

 the Hall effect. In the case of Plate 4, as explained above, the value 

 of the thickness given, being calculated from the resistance, is not con- 

 sidered accurate. The current density is given in c.g.s. electromag- 

 netic units of current per square centimeter of cross section of plate. 

 The Hall effect is given as above in c.g.s. units. 



Current Density. 



Plate 1 



Plate 2 



Plate 3 



Plate 3 



April 23 

 May 1G 



April 30 



May 7 

 June 20 

 June 23 



(3.9 

 3.1 



I 5.0 

 U.07 



6.0 



( 10.9 

 27.4 

 151. 



580. 

 v 860. 



( 8.6 

 \C10 



/ 9.1 

 \670 



/ 9.1 

 [670 



Hall Effect. 



0.00074 

 0.00073 

 0.00063 

 0.00079 



0.00071 



0.00066 

 0.00062 

 0.00062 

 0.00062 

 0.00066 



0.00063 



0.00062 



0.00064 



0.00068 



0.000655 



0.000695 



0.000647 0.000660 



