MACHINE, 
The rubber is usually a piece of wood fit- 
ted to the surface intended to be subjected 
to friction, and covered first with two or 
three thicknesses of elastic cloth, then with 
smooth leather, and lastly with a flap of 
silk, pasted upon the edge at which the 
glass in its rotation arrives, and passing 
loose over the face of the cushion, and 
thence upon the surface of the glass, as far 
as the commencement of the (irime con- 
ductor. Its use has been explained under 
the article Excitation. 
In fig. 1, Plate Machine Electric, A repre- 
sents tl)e glass cylinder of a machine, tin ned 
by, B, the handle. Its surface rubs against, 
C, the cushion, from which proceed, D, the 
silk flap, and the electricity is conveyed to,' 
E, the prime conductor. The supports of the 
cylinder, the cushion, and (indispensably) 
of the prime conductor, are made of glass or 
baked wood, in order that the electricity may 
not be conveyed to the earth, unless when 
the operator chooses to make the commu- 
nication by some condneting body. A prime 
conductor is sometimes applied to the rub- 
ber. 
Though we liave produced as strong an 
excitation as we have ever heard of, by the 
amalgam of meicuiy and zinc, with a little 
tallow, as mentioned under the article Ex- 
citation, yet as maily electricians, parti- 
cularly tlie experienced Mr. Cuthbertson, 
prefers tin and zinc, and it is probable, that 
this mixture may afford a speedier oxyda- 
tion ; we shall give his receipt. 
Melt two parts of tin and zinc in a cruci- 
ble, and pour them on two parts of mercury 
in a wooden box made for that purpose, 
which close and agitate till the metals are 
cold. Then pulverize the granulated mass 
very finely, and make it into a paste with 
hog's lard. 
Fig. 2, shews the plate machine, with Ni- 
cholson’s cylinder improvements for chang- 
ing the two states at pleasure, as adapted 
by Dr. Von Marum, of Haerlem. 
The glass plate, G G, is fastened to the 
axis, B B, by means of a screw on the axis 
passing through a hole in the centre of the 
plate, and secured by a nut, C, on the op- 
posite side. The axis is supported by a 
fingle pillar. A, which for this purpose is 
provided with a bearing piece, K, on which 
are two brass collar pieces, that carry the 
axis; and on the end of the axis, opposite 
the glass, is a counterpoise, O, of lead, to 
prevent too great a friction in the coilar 
nearest the handle. The arc of tlie con- 
dactor, E E, which carries the two small re- 
ELECTRIC. 
ceiving conductors, FF, is fixed to an axi.<( 
turning in the ball, H. On the othei- side of the 
plate is the otlitr arc, I, of brass wire, fixed 
in the bearing piece, K, but so as to admit 
of being turned round like tlie arc EE. P 
is a copper tube, moving like a radius on 
the stem of the ball, .S, which, being screw- 
ed into the conductor, II, serves to confine 
the arm, P, in any position that may be re- 
quired. Tlie dissipation of electricity along 
the glass supports is prevented by a kind 
of cap, T, of mahogany, which affords an 
electrical well or cavity underneath, and 
likewise effectuall)' covers the metallic cap 
into wiiich the glass is cemented. The 
lower extremity of the pillar is guarded in 
the same mariner by a hollow piece or ring 
of mahogany, V. The three glass pillars 
are set in sliding pieces, M'^WW, adjustable 
by screws ; at each extremity of the hori- 
zontal diameter of the plate are two rub- 
bers, X, one on each side, pressed regularly 
and uniformly against the plate by means 
of a spring, Y, the force of pressure of 
wliich is regulated by means of a screw. 
To these rubbers are attached silk flaps, 
Z Z, those of one pair of rubbers descend- 
ing, and tliose of the other pair ascending, 
in the direction in wliich the plate is work- 
ed. A piece of fine dry writing paper, as 
long as the rubber, and half an inch 
broader, so as to cover the seam that fas- 
tens the silk to the leather, allows greater 
pressure to be employed by diminishing 
the friction, and prevents both the glass and 
silk from being soiled by the amalgam, so 
that the excitement is more pow'erful, and 
the amalgam requires to be renewed less 
frequently. As the semicircular branch of 
the prime conductor is moveable, it may be 
made to exhibit Ihe electricity of the rub- 
ber at any time, by placing the cylindri- 
cal ends in contact with the cushions, the 
semic^ular wire, I, being at the same time 
turnM so as to cross it at riglit angles, 
which insulates the cushions. M'hen the 
conductor is required to give electricity 
from the glass, the arc I must be in contact 
with the cushions, and the arc E E perpen- 
dicular to the horizon. 
If the insulated prime conductor of a 
machine be well polished, and without cor- 
ners or angles, it will retain its electric state 
very well, and will emit strong sparks upon 
the approach of any uninsulated conduc- 
tor. If the uninsulated conductor be broad, 
round, and polished at the ehd, the sparks 
will be short and dense, and will produce a 
considerable sound ; if less broad, the spark 
