128 Whitehead — Magnetic Effect of Electric Displacement. 



_ 2 V2 . 8800 27r . 133 . 10' 1 

 ^ "" 4^ * 2 . 45 • '(3><10^yTcP * ^ 



and the total amount is 



6-45 q= 3-34 X 10"' amperes. 



The experiment was tried with paraffin and with hard rubber 

 and no sound conld be detected in either case. The question 

 whether the telephone receiver would respond to such a small 

 current was of course still open, nor could it be completely 

 answered. The following approximation was, however, made : 

 a conductor was placed through the opening of the iron annulus 

 and included in a circuit with an ammeter, a resistance, and a 

 source of alternating electromotive force in low values ; the 

 lowest division on the ammeter scale was '02 amperes, and the 

 voltage was adjusted to give this reading, the telephone receiver 

 giving a good note. Resistance was then inserted by steps up 

 to about 100 ohms (inductive), apparently bringing the ammeter 

 needle to zero ; sound in the telephone receiver was still audi- 

 ble, though faint. The experiment was performed very roughly 

 and hurriedly, and is susceptible of considerable improvement. 



The writer's thanks are extended to Professor Ames for his 

 interest and kindness in furnishing every facility needed in the 

 course of the investigation. 



The mechanical work was done by Mr. Charles Childs ; for 

 his skill and interest at all times the writer wishes to extend 

 his appreciation. 



It is proposed to carry this work further in both forms of 

 apparatus. 



Physical Laboratory, 



Jolins Hopkins University, 



May, 1902. 



