Instruments and Experiments. 107 
ished by inserting them in a tube of glass or other non-conduct- 
ing substance, before introducing them into the helix. A 
When a bar of iron is contained in the helix, and a small key 
‘orsome nails are applied to one end of it, notwithstanding its 
magnetic attraction is intermitted every time the voltaic circuit 
is broken, yet, it being almost instantaneously renewed, they do 
not cease to be sustained. This experiment succeeds best when 
the iron bar is enclosed in a brass tube previously to being intro- 
duced into the helix, the closed cincaile of the tube tending to 
prolong its magnetism. ' 
The double helix and electrotome, in consequence of being 
provided with a mechanical contrivance for breaking the battery 
circuit, may be used with a very small battery, although its effects 
are of course most striking, when used with a powerful one. If 
avoltaic pair, consisting of a silver dollar anda piece of rolled 
zine of the same size be used, and the helix be filled with soft 
iron wires, the shock is quite severe. 
Water may be decomposed by connecting the outer helix with 
an instrument for that purpose having very small platinum wires 
guarded with glass, as originally used by Wollaston. The ex- 
tremities of the platinum wires, while the decomposition is going 
on, appear in a dark room, one constantly and brightly, and the 
other intermittingly and feebly luminous. If the apparatus for 
decomposition is removed out of the noise of the double helix 
and electrotome, rapid discharges are heard in the water, produ- 
cing sharp ticking sounds, audible at the distance of eighty or 
ahundred feet, and synchronous with the ruptures of the vol- 
taic circuit. Decomposition is effected both»by the initial and 
terminal secondary currents, that is to say, by the currents indu- 
ced both on completing and on breaking the battery circuit ; but 
the ticking noise and sparks accompanying the rapid discharges 
in the water, are produced only by the terminal secondary cur- 
rent, Hydrogen may be kindled and brilliant scintillations pro- 
duced by the double helix and electrotome. A Leyden jar, the 
nob of which is connected with the inside coating by a contin- 
ash Wire, may be- feebly charged, and slight shocks be rapidly 
"scelved from it, by bringing the knob in contact with one of the 
cups of the outer helix, and grasping with the two hands respec- 
tively the outer coating of the jar and a handle connected with 
the other cup. The instrument is likewise very convenient for 
