Electro-Magnetic Experiments. 413 
of a galvanometer ; this roll is represented in the lower part of the 
figure as placed upon the uorth pole of a horse-shoe magnet, by 
passing it to and fro upon the leg of the magnet, or by alternately 
removing and replacing it upon the pole, a vibration is produced in 
the needle of the galvanometer. ‘The wires are continued to such a 
length as to prevent the direct action of the magnet upon the needle 
of the galvanoineter. 
Some experiments which by the kindness of Mr. Lukens I was en- 
abled to make with this apparatus resulted in a satisfactory mode of 
representing the effect which is produced upon the galvanometer in 
any given position of the coil. I offer it simply as a mode of recollect- 
ing the results of observation. 
The coil of wire (fig. 2,) was first applied to the north pole of the 
magnet, the direction of the coil being from right to left above the mag- 
net, the inside wire of the coil was on the left hand, the outside wire on 
the right, the experimenter facing the north; the outside wire was car- 
ried to the south cup of the galvanic multiplier, the inside to the north 
cup. ‘The poles of the magnet were turned to the south. On with- 
drawing the coil from the pole, the north pole of the needle was de- 
flected to the west, returning the coil carried the same pole to the east. 
Changing the wires of the coil in the cups of the galvanometer revers- 
ed the direction of the vibration of its needle. 
The effect of withdrawing the coil would have been produced by a 
galvanic current passing through the coil from left to right below the 
magnet, from right to left above it. 
The coil was next changed from right to left, that is, the direction 
of the coil changed so that it passed from right to left below the mag- 
net, and from left to right above it, the wires which dipped into the 
cups of the multiplier remained in their places; the inner wire was 
now to the right hand, the outer wire to the left. On removing the 
coil from the north pole of the magnet, the north pole of the needle 
of the multiplier passed to the east, on returning the coil the same pole 
moved to the west. 
This effect would (as before,) have been produced by a galvanic 
current passing from left to right below the magnet, from right to left 
above it. The other positions of the coil being examined showed that 
they might be represented by the same supposition of a circular cur- 
rent about the pole of the magnet, and passing through the wire. The 
reverse of such a hypothesis is of common application to represent the 
Vou. XXII.—No. 2. 53 
