106 New Electro- Magnetic and Magneto-Electric 



cannot be endured a moment even by the firmest nerves. The 

 intensity of the shock may be varied at pleasure by varying the 

 number of the iron wires in the helix, the addition of a single 

 wire producing a very manifest effect. If the brass tube be lon- 

 gitudinally divided on one side, it no longer diminishes the shock 

 or spark. 



The neutralizing influence of the outer helix, when its ex- 

 tremities are connected by means of a copper wire, admits of 

 very satisfactory explanation on the principles discovered by Prof. 

 Henry, and fully explained by him in his highly valuable paper 

 published in the No. of this Journal for April last. On breaking 

 the battery circuit, a secondary current being induced in each 

 helix, and flowing in the same direction with the voltaic current, 

 the secondary current in the outer helix tends to produce a ter- 

 tiary current in the inner one flowing against the secondary, and, 

 as shown by the diminution of the spark and shock, counteract- 

 ing in a great measure its effect. Secondary currents, as was 

 shown by Prof. Henry in a similar case, are likewise induced in 

 the undivided brass tube, and produce a similar counteracting 

 effect. The closed circuits must also act as a feeble prolongation 

 of the battery current, and thus prevent that sudden neutraliza- 

 tion of the magnetism of the enclosed iron bar or wires, which 

 is essential to the bright spark and strong shock. 



The superiority of a bundle of wires over a bar of iron, was 

 discovered nearly at the same time by Dr. Page in this country, 

 and by Mr. Bachhoffner in England. Dr. Page ascribes it to the 

 mutual neutralizing action of similar poles, and the consequent 

 greater suddenness of the change, which, at the moment the bat- 

 tery current is broken, takes place in the iron wires. To this 

 cause must be added the absence of the closed circuits which are 

 induced in the iron bar. I have not been able to perceive much 

 advantage in insulating the iron wires contained in the helix, as 

 was done by Mr. Bachhoffner. The eftect of an iron bar in in- 

 creasing the shock and spark, is very much enhanced by sawing 

 it longitudinally on one side to the axis, by which the closed 

 circuits, otherwise induced in it, are in a great degree prevented. 

 An iron tube one eighth of an inch in thickness, produces a 

 greater effect than a solid iron bar of the same diameter, though 

 less than when the helix is equally filled with iron wires. The 

 effect of an iron bar or of a bundle of iron wires, is not dimin- 



