368 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



the trausverse effect with the primary current. The observations were 

 taken in the same manner as with Plate 1. The first set of observations, 

 in which the main current, I, was increased by steps from 0.02 ampere 

 to 1.59 amperes, gave the following results : 



April 30. Plate 8; thickness 0.000184 cm. 



As these results were somewhat irregular, it was determined to make 

 measurements with weak and strong currents alternately. In the follow- 

 ing set of measurements the readings of the ammeters for the weak 

 current were taken at about one-sixth of the full scale reading for the 

 Weston ammeter, and about one-tenth of the full scale reading for the 

 Siemens and Halske ammeter. 



Mat 7. Plate 3. 



On account of the position of the ammeter scale readings for weak 

 currents, these measurements are not considered as accurate as the 

 succeeding measurements. 



Plate No. 4 was very kindly prepared by Professor Hall. The 

 metliod adopted was the same as that in preparation of the plate in which 

 the phenomenon was discovered. A glass plate was covered with a thin 



