1840] WRITINGS OF JOSEPH HENRY. 1G7 



being interposed, the small particles of iron were attracted 

 by the end of the needle, indicating a feeble, temporary- 

 development of magnetism. Hence the current which moves 

 the needle, and is not neutralized by the interposed plate, 

 also feebly magnetizes soft iron, but not hard steel. 



49. Again, the arrangement of apparatus being as in para- 

 graph 46, instead of a plate of zinc, one of cast iron, of about 

 the same superficial dimensions, but nearly half an inch 

 thick, was interposed ; with this, the magnetizing power of 

 the spiral, in reference to tempered steel, was neutralized; 

 and also the action of the galvanometer was much dimin- 

 ished. 



50. Another result was obtained by placing in the circuit 

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

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

 magnetizing 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 

 galvanometer in these instances, was partially intercepted by 

 the imperfect 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, and 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. 1, connected with the battery, was supported perpen- 

 dicularly 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 galvano- 

 meter and the spiral that the induced current from the one 



