134 Contributions to Electricity and Magnetism. — 
° 
four degrees. In addition to these, the body was also introduced 
into the same circuit; the shocks were found very severe, the 
spiral magnetized needles strongly, but the galyanometer was 
still less moved than before. The current of low intensity, 
which deflects the needle of the galvanometer in these instances, 
was partially intercepted by the imperfect conduction of the wa- 
ter and the body. 
51. 'To exhibit the results of these experiments with still more 
precision, an arrangement of apparatus was adopted similar to 
that used by Dr. Faraday, and described in the fourteenth series 
of his researches, namely, a double galvanometer was formed of 
two separate wires of equal length and thickness, and wound to- 
gether on the same frame ; and also, a double magnetizing spiral 
was prepared by winding two equal wires around the same piece 
of hollow straw. Coil No. 1, connected with the battery, was 
supported perpendicularly on a table, and coils Nos. 3 and 4 were 
placed parallel to this, one on each side, to receive the induction, 
the ends of these being so joined with those of the galvanometet 
and the spiral that the induced current from the one coil, would 
pass through the two instruments, in an opposite direction to that 
of the current from the other coil. The two outside coils were 
then so adjusted, by moving them to and from the middle coil, 
that the induced currents perfectly neutralized each other in the 
two instruments, and the needle of the galvanometer and that 
in the spiral were both unaffected when the circuit of the battery 
was made and broken. With this delicate arrangement the 
slightest difference in the action of the two currents would be 
rendered perceptible ; but when a zinc plate was introduced e0 
as to screen one of the coils, the needle of the galvanometer still 
remained perfectly stationary, indicating not the least action of 
the plate, while the needle in the spiral became powerfully mag- 
netic. When, however, a plate of iron was interposed instead of 
the one of zinc, the needle of the galvanometer was also affected. 
52. From the foregoing results it would seem that the secol- 
dary current, produced at the moment of suddenly beginning 
ending of a galvanic current, by making and breaking contact 
with a cup of mercury, consists of two parts, which possess dif- 
ferent properties. One of these is of low intensity, can be intet- 
rupted by a drop of water, does not magnetize hardened steel 
needles, and is not screened by the interposition of a plate of any 
2 
wee. 
