MACHINE, ELECTRIC. 
®ver the surface of the glass which projects The vapours of the atmosphere are con 
oil every side ; but if the glass plate be tliin, tiiiually attaching themselves to the surface 
in which case, at an equal intensity, it ad- of cold glass, and by that means destroy the 
mits of a much greater charge, the dis- electricity. Sulphur, wax, or resin bein'! 
charge will be made through its substance. less subject to this, retain their electric state 
Glass, as thick as one eighth of an inch, may much longer. A plate of glass or wood 
be penetrated by this means, one or more coated over with any substance of this na- 
holes being made where the electric matter ture, may be excited by friction, and will 
has passed, in which holes the glass is pul- 
verLsed, and may be picked out with a pin. 
It is not possible to charge an electric 
plate by inducing an electric state on one 
of its surfaces, unless the other be at the 
same time sufficiently near to a non-electric 
to assume the contrary state by emitting or 
receiving the electric matter. 
If a plate of glass be laid upon an uninsu- 
lated plate of metal, the upper surface may 
be rendered electric by friction, or by ap- 
plying an electrified body successively to its 
parts. This electricity may be taken off by 
touching the upper surface with an uninsu- 
lated metallic plate of the same dimensions 
as that upon which the glass is placed, but 
will not be entirely taken off, because the 
communication between the two surfaces in 
this method is not perfect, and because the 
metal cannot by ordinary means be brought 
into actual contact with the glass. The 
small quantity which remains, produces an 
effect which has been mistaken for a perpe- 
tual electricity. For if a plate of metal, to 
which a glass handle is affixed, be laid upon 
the glass, this small quantity of electricity 
will influence the metal, and, without actual- 
ly communicating the electric matter, will 
cause it to exhibit a similar state. If this 
be taken off, by drawing the spark, and the 
metal then removed, by means of the glass 
handle, it will be found possessed of the 
contrary state of electricity, and another 
spark may be obtained. The metallic plate 
may be then again applied to the surface of 
the glass, and the process again repeated, 
and so on for a prodigious number of times, 
without any sensible difference in the event. 
For the electricity at the surface of the 
glass being almost in tire natural state, as to 
condensation, does not disappear- for a very 
long time, and the very near approach of 
the metal enables it to produce the same 
effect as would be obtained at a greater 
distance from a stronger electricity. This 
is made obvious, by bringing the metallic 
plate near the surface of the glass before 
its first strong electricity is taken off, for the 
same event is then perceived at the dis- 
tance of four, five, or six inches, as in the 
former case is produced by contact. 
produce electricity in a metallic plate, in the 
manner above described, for a very great 
length of time. Such a plate, together with 
its metal, has been named the electropho- 
phorus, fig. 3. 
If the discharge of an electrified plate be 
made by the parts of a living animal, a con- 
siderable pain will be felt chiefly at the ex- 
tremities of the muscles. For example, if 
the lower metallic plate be touched with 
one hand, and the other brought to the up- 
per plate, at the instant of the emission, a 
pain will be felt at the wrist and elbows, 
which as instantly vanishes. If a larger 
glass plate be ussd, the pain will be felt on 
the breast; if yet larger, the sensation vvill 
be that of a universal blow'. This sensation 
has obtained the name of the shock, and 
will deprive animals of life, if sufficientlv 
strong. The shock from thirty square in- 
ches of glass, well charged, will instantly 
kill mice, sparrow's, or other small animal^ 
Six square feet of glass will deprive a man 
of sensation for a time, if the head be made 
a part of the circuit through which the elec- 
tricity moves. No inconvenience has been 
found from the electric shock by men of 
strong habits ; but women of delicate con- 
stitutions have had convulsions from a vio- 
lent shock. Itmay be observed, that the elec- 
tric shock is a propf that the electric matter 
can pass through the substance of non-elec- 
trics, and is not universally conducted along 
the surfaces alone, as some have supposed. 
The object of the philosopher being, in 
general, to collect a large quantity of elec- 
tricity, by means of the surfaces of electrics, 
it is more usual to employ jars, and not 
plates. These are made of various shapes 
and magnitudes; but the most useful* are 
thin cylindrical glass vessels, about four 
inches in diameter, and fourteen in height, 
coated within and without with tin-foil, 
which is stuck on with gum-water, paste, 
or wax, excepting two inches of the rim or 
edge, which is left bare, to prevent the 
communication between the coatings. A- 
bout four inches from the bottom, within. 
Is a large cork, that receives a thick wire, 
ending in several ramifications, which topch 
the inside coating; the upper end of the 
