= Rotation of Equipotential Lines of Electric Current. 419 
velocities, as in (91). For D, &. write B, &.; and we have 
the same equations for the induction directions. For Dj, &c., 
write c,H,, &., and the resulting equation gives the directions 
of EK. For D,, &e., write ju, Hy, &c., and the resulting equation 
gives the directions of H. 
XLVI. On the Rotation of the Equipotential Lines of an 
Electric Current by Magnetic Action. By HE. H. Hatt, 
Instructor in Physics at Harvard College*. 
N this article the results will be given of experiments 
made during the month of August 1883, and at intervals 
since, in the Physical Laboratory of Harvard College. The 
substances which have been chiefly examined are copper, zinc, 
certain of their alloys, and iron and steel. Some mention will 
be made also of gold, cobalt, nickel, bismuth, and antimony. 
In most cases when possible the metal was used in the form 
of a thin strip, about 11 centim. wide and about 3 centim. 
long, between the two pieces of brass B, B (fig. 1), which, 
soldered to the ends of the strip, served as electrodes for the 
entrance and escape of the main current. To the arms aq, a, 
about 2 millim. wide and perhaps 7 millim. long, were soldered 
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the wires w, w, which led to a Thomson galvanometer. ‘The 
notches c, c, show how adjustment was secured. The strip 
thus prepared was fastened to a plate of glass by means of a 
cement of beeswax and rosin, all the parts shown in the figure 
being imbedded in and covered by this cement, which was so 
* From Silliman’s American Journal, February 1885. 
