= 
: ; * * + 
Instruments and Experiments. 105 
tremity of the helix, pass down through the base-board, under- 
neath which they are soldered to the’ cup c. The similar ends 
at the other extremity of the helix, likewise pass down through 
the base-board, underneath which they are connected with the 
middle brass band e, which is surmounted with a brass cup con- 
taining mercury. Into this cup descends a copper wire s, con- 
nected above with the wire w, w, which by means of clock-work 
set in motion by a concealed spring, wound up at the milled head 
d, is made to vibrate rapidly, and to dip alternately into glass 
cups for containing mercury. The glass cups are open at bot- 
tom, so as to allow the mercury to be in contact with the brass 
Supports, into which they are cemented, and which are fastened 
tothe outer brass bands b and b’.. These brass bands are con- 
nected underneath the base-board: with a cup ¢’, not seen in the 
figure. and corresponding toc. Both the cups ¢ and c’, are fur- 
nished with binding screws to confine the wires by which the 
inner helix is connected with the battery. 
Exterior to the helix just described, enclosing it and insulated 
from it, is another composed of about two thousand feet of small 
insulated wire, the two extremities of which are soldered to the 
Cups m and m/, likewise furnished with binding screws. H and 
H’ are handles for shocks, connected with the cups m and m/. If 
we how suppose the copper pole of a voltaic battery to be con- 
hected with the cup ¢, and the zine pole with the corresponding 
cup ¢’, the battery current will circulate unbroken through the 
Several strands of wire composing the inner helix, to one of the 
outer bands; thence by the vibrating wire to the middle band, 
and thence to the cup ¢, whenever either end of the vibrating 
Wire dips into the mercury of the glass cups. As the vibrating 
Wire approaches to a horizontal position, previously to the other 
end’s dipping into the mercury of the other glass cup, the battery 
current is broken, anda bright spark is seen in the cup, in which 
the rupture of the current has just taken place. If the handles 
© gtasped with moistened hands, severe shocks will be felt. 
Introduce into the helix a brass tube, and the spark becomes 
=— small, and the shock feeble. Next introduce a bundle of 
“it iron wires into the brass tube, and the spark and shock are 
not sensibly increased. If the tube be now withdrawn from 
the helix without withdrawing the iron wires, the spark will be- 
come exceedingly brilliant, and the shocks so severe that they 
Vol. x1, No. 1.—Oct.-Dec. 1840. 14 
