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 galvanometer 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 galvanometer 

 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 dehcate arrangement the 

 slightest difference in the action of the two currents would be 

 rendered perceptible ; but when a zinc plate was introduced so 

 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 secon- 

 dary current, produced at the moment of suddenly beginning or 

 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 inter- 

 rupted by a drop of water, does not magnetize hardened steel 

 needles, and is not screened by the interposition of a plate of any 



