Resistance of Bismuth to Alternating Currents. 557 



3rd, that this field-strength is considerable — 4500 lines 

 per sq. cm. This latter result is also interesting from the 

 fact that Lenard and others, using very high frequencies,. 

 have found a negative effect in no field ; with the low 

 frequencies used in my experiments the negative effect can 

 just be detected, but could not be satisfactorily measured. 



Temperature Variations. 

 Experiments were next undertaken to find the effect of 

 temperature variations on the bismuth E.M.F. 



In all the previous experiments a Hartmann &, Braun 

 bismuth spiral, designed for field-testing, had been used, but 

 this became useless when experiments were made at other 

 than atmospheric temperatures, so it was replaced by a wire 

 *3 mm. in diameter and about 10 cm. long, bent into the form 



Fis. 5. 



of a flat grid and soldered to two thick copper wires (fig. 5). 

 These grids were very easily broken, and a number were used 

 during the experiments ; the bismuth wire was supplied by 

 Messrs. Hartmann & Braun. 



For temperatures above atmospheric a grid was placed in 

 a glass vessel (fig. 6) consisting of an inner vessel having a 



Fiar. 6. 



fiat tube joined on at the bottom, into which the bismuth 

 wire projected, surrounded by a similar slightly larger vessel. 



