108 New Ellectro-Magnetic and Magneto-Electric ~ 
showing the Spark of a magneto-electric machine, that is fur- 
nished with the contrivance, called by Dr. Page a unitrep, for 
causing the current induced by the magnet to flow in a constant 
direction. By making the proper connections, the magneto-elec- 
tric current may be made to circulate through the inner helix in- 
the same way as the voltaic current, producing sparks in the glass 
_eups, and, if the handles connected with the outer helix be grasp- 
ed, slight shocks. In addition to the experiments I have enume- 
rated, the double helix and electrotome may be used for most of 
the purposes of a common simple helix. ) ui 
eparable Helices and Revolving Armature.—This instru- 
ment, represented by figure 2, is similar in many respects to the 
preceding, and will require but little description. The two heli- 
ces are composed of wires of about the same length and size, as 
those of the double helix and electrotome, but entirely discon- 
nected with each other, so that the outer may be removed from 
the inner one. ‘The latter is firmly secured in a vertical position 
to a base-board, underneath which one set of similar ends of its 
wires is soldered to the cup A, and the other set to the cup B. 
R R isa steel rasp, confined in close contact with the cup B. 
P P is a modification of Page’s revolving armature, described in 
Vol. xxxv, p. 262, of this Journal. The extremities of the wire 
wound round the two branches of the electro-magnet, are respec 
tively connected underneath the base-board with the cups Band O. 
The voltaic current may be transmitted in sequence through this 
instrument and the inner helix, by connecting the cups, A and ©, 
with a battery. It is here used to break the battery current, 
which it does twice during each revolution of the armature 
The battery current may be broken, without including the revol- 
ving armature in the voltaic circuit, by connecting one of the 
battery wires with the cup A, and drawing the end of the otbet 
over the steel rasp, in which case brilliant scintillations will be 
produced. § and 8 are cups fastened to brass caps, longitudin- 
ally. divided, which enclose the ends of the outer helix, and t0 
which the ends of the wire composing it are soldered. In the 
figure there is seen, projecting from the upper end of the innef 
helix, a brass tube filled with iron wires, which may be with- 
drawn. This instrument is peculiarly suited to the lecture-room 
on account of its simplicity, and the facility with which the 
powers and uses of its several parts may be separately exhibited. 
