to Electricity and Magnetism. 497 



of the helix (fig. 3.)> at the same time, the galvanometer, the 

 spiral, and a drop of distilled water ; with these the magneti- 

 zing power of the spiral was the same as without the water, 

 but the deflection of the galvanometer was reduced from ten 

 to about 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 galvanome- 

 ter in these instances, was partially intercepted by the imper- 

 fect conduction of the water 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 galvano- 

 meter was formed of two separate wires of equal length and 

 thickness, wound together 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. J, 

 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. Tiie 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 

 so as to screen one of the coils, the needle of the galvanome- 

 ter still remained perfectly stationar}', indicating not the least 

 action of the plate, while the needle in the spiral became 

 powerfully magnetic. When, however, a plate of iron was 

 interposed instead of the one of zinc, the needle of the galva- 

 nometer was also affected. 



52. From the foregoing results it would seem that the se- 

 condary current, produced at the moment of suddenly begin- 

 ning or ending of a galvanic current, by making and breaking 

 contact with a cup of mercury, consists of two parts, which 

 possess different properties. One of these is of low intensity, 

 can be interrupted by a drop of water, does not magnetize 

 hardened steel needles, and is not screened by the inter})ositioii 



PhiL Mag. S. 3. Vol. 18. No. ] 19. Jme 1811. 2 K 



