476 The Etv. N. J. Callan ofi a ncio Galvanic Battery. 



of plates unless they are large. The electro-magnet which 

 I first used was a straight bar of soft iron, about 2 feet long, 

 and an inch thick. On this bar were coiled two copper wires, 

 each about 200 feet long. The voltaic battery consisted of 14< 

 pairs of zinc and of as many double copper plates : each plate 

 was about 7 inches square. The end of the first coil and the be- 

 ginning of the second were immersed into the same cup of mer- 

 cury, the voltaic current was passed through the first coil only, 

 and the shock was taken by making a communication with the 

 beginning of thefirst coilandwith theendof the second. When 

 the current of electricity was passed through the helix from 

 one pair of plates, the shock received on breaking contact with 

 the battery was equal to that of a battery containing 20 pairs of 

 plates. When two pairs of plates were used, the shock ap- 

 peared to be doubled ; with three voltaic circles, it appeared to 

 be trebled; and with every increase in the number of voltaic 

 circles, there appeared to be a proportional increase of the 

 shock. With the li pairs of plates the shock was so strong 

 that a person who took it, from an electro-magnet on which 

 therevverefour coils of wire, felt the effects of it for several days. 

 With a battery of 4-inch plates the shock increased with the 

 number of plates, but not so rapidly as when large plates were 

 used. I am inclined to think that with a battery of 4-incli 

 plates, the shock increases but little when the number of plates 

 exceeds a hundred. I could not induce any one to take the 

 shock from the electro-magnet when a greater number than 16 

 of our large plates were used. With 1 6 of them the shock was 

 exceedingly strong, although the acid mixture employed in 

 charging the battery was very weak ; and, from experience, I 

 know that the electro-magnetic effects of a battery depend very 

 much on the strength of the charge. 



From all the experiments which I have made on the mag- 

 neto-electric shock, 1 think I may fairly conclude, that, if 2000 

 feet of wire were coiled on a bar of soft iron 6 feet long and 

 an inch thick, a shock might be obtained with the aid of a 

 single pair of plates, which would equal that of a battery of 

 100 voltaic circles. Hence, since the shock increases in pro- 

 portion to, or, at least, very rapidly with the number of plates, 

 when they are large, the shock given by such an electro-magnet 

 magnetized by our battery of 20 pairs of plates, should nearly 

 equal, or perhaps exceed that of a battery of 1000 voltaic cir- 

 cles. Hence, by our battery of 20 pairs of plates, an electric 

 current of the highest intensity may be produced. This bat- 

 tery then sup|)lies the place of all the various kinds of galvanic 

 batteries. 



The shock given by the electro-magnet may be obtained 



