Hall Effect in Liquid and Solid Mercury. Ill 



(a) which changes sign with the intensity of the magnetic 

 field ; a second (ft) which changes sign with the primary 

 current ; and a third (7) which reverses with both the field 

 intensity and the current. 7 has the characteristics of the 

 Hall effect. If these are the only effects present 



A + B + C + D = (1) 



If only a and /3 exist, that is, if the Hall effect is zero, 



A + C = B + D = (2) 



Liquid Mercury. — Three different cavities for holding the 

 mercury were used ; several sets of readings were taken 

 with each. The strength of the magnetic field ranged from 

 3ibout 10,000 gausses to 22,400 gausses ; the primary current 

 from 0*14 ampere to 3*07 amperes. Although the work on 

 the first two cavities indicated the absence of the Hall effect, 

 the unsteadiness of the galvanometer was such that one 

 ■could not say with certainty that the observations indicated 

 a coefficient smaller than O'OOOIO electromagnetic unit. 

 With the third cavity, however, the steadiness and the 

 sensitiveness were improved. A pressure of about three 

 hundred grams per sq. cm. was applied to the mercury in 

 the cavity. (Greater pressure produced no improvement.) 

 Headings were taken with this cavity which satisfied exactly 

 equations (1) and (2). Due allowance being made for un- 

 steadiness, which prevented readings being taken to less than 

 \ mm., we find that this experiment indicates the absence 

 of a Hall effect in liquid mercury with a coefficient larger 

 than 0*00002 electromagnetic unit, one-half the smallest 

 value Amerio could observe. 



Solid Mercury. — In this part of the work the galvanometer 

 was much more nearly steady than before. The thermal 

 electromotive force in the circuit was large, but was very 

 nearly constant. No vibration of the image could be 

 detected, but in some cases there was a slight drift which 

 was easily compensated. By taking these precautions 

 readings were easily taken to one-fifth mm. 



Two different strengths of field, 12,100 and 10,000 gausses 

 respectively, and two different strengths of primary current, 

 2*00 and 3'93 amperes respectively, were used. In each case 

 A = B = C = D = 0, showing that a. — ft — 7 = 0. 



The thickness of the sheet of mercury was 0'080 cm. 

 The electromotive force which would produce one mm. 

 •deflexion on the galvanometer scale was 3 23xl0~ 8 volt. 

 The Hall coefficient R which, if present, would produce 



