394 Messrs. Cross cmd Williams 07i the Strength of the 



Fig. 1. 

 Ferrotype Iron. 



Fig. 3. 

 Steel. 



Induced Current. 



30 40 50 60 

 Induced Current. 



and \ of an inch in diameter, and the diaphragm an ordinary 

 disk of ferrotype iron 2-^^ inches in diameter and -j^q of an 

 inch thick (No. 31 B.W. &.). 



Table I. gives the data from which fig. 1 was constructed. 

 The strength of field is given in terms of the tangents of the 

 anoles of deflexion of the magnetometer-needle. The induced 

 current is given in arbitrary units, as only relative values are 

 needed. A determination of the value of the deflexions was 

 made by observing the excursion due to the discharge of a 

 condenser through the ballistic galvanometer, and it was 

 found that the abscissa 100 on the curves corresponds to a 

 sudden discharge of approximately 0'00000097 of a coulomb 

 through the coils of the galvanometer. 



