‘ee 
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 ate 
induced in the iron bar. I have not been able to perceive much 
advantage in insulating the iron wires contained in the helix, % 
was done by Mr. Bachhoffner. The effect of an iron bar in i 
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 4 
greater effect than a solid iron bar of the same diameter, though 
Jess than when the helix is equally filled with iron wires. 
effect of an iron bar or of a bundle of iron wires, is not dimlt- 
ye 
