354 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



H is the horizontal intensity of the earth's field, about 0.19 ; C is the 

 strength of the primary current; M is the strength of the magnetic field ; 

 c is the current through the Thomson galvanometer. 



This showed the general law of the phenomenon for a plate of a given 



, ^ C X 1/ , , . , 



thickness, smce it showed to be at least approximately a con- 

 stant within the range of primary current used. 



Righi * made a series of measurements maintaining the magnetizing 

 current constant. He used gold, which he prepared according to the 

 method of Professor Hall. He found the effect observed proportional 

 to the current, except for weak currents, for which the eiFect was 

 relatively greater. The differences were always very small and Righi 

 thought that they might have been due to some unknown error. The 

 tabulated results are not given in his paper. 



Leducf made a similar series of experiments on bismuth. The trans- 

 verse difference of potential caused by the introduction of the magnetic 

 field was measured with a capillary electrometer. The following table 

 of results is given. 



C is the intensity of the current in the electromagnet ; / is the in- 

 tensity of the primary current in the plate ; E is the difference of 

 potential at the secondary electrodes, caused by the magnetic field. 



* Meniorie della Accademia delle Scienze di Bologna, p. 115 (1883). 

 t Comptes Rcndus, 98, 673-675. 



