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8 HOW TO MAKE ELECTRICAL MACHINES.
~ wire about a quarter of an inch Jong, filed to a point, to the’
sides of the rod nearest the glass plate, as‘shown in Fig. 6,
80 that the plate revolves between a double row of points,
which can be done with solder, and the machine is complete.
The conductor can further be improved by inserting at the
opposite end a small piece of brass rod two and a half in-
ches high, surmounted by a ‘brass ball, which is useful in
some experiments. Care must be taken that the. unfoil of
the conductor overlaps the brass rod at either end, and thus
~ forms a metallic connection. If this is not done the con-
ductor will not become charged sufliciently. If the conduc-
tor can be made of brass it will work better still, as a me-
tallic connection is then insured. The conductor can be
fastened to the glass rod on which it is supported by ‘‘ Prout’s
elastic glue,” or other cement, a hole being made in the cen-
ter of the bottom of the conductor, and another in the stand .
of the machine for opposite ends of the glass rod. .
The machine having been constructed, afew words will be
useful in how to work it. Warmth and dryness are, above
all things, essential. If the air of the room -is damp it will
be nearly impossible to obtain any result. Before working,
the glass plate must be thoroughly warmed, taking care not
to crack it, by being placed endwise before a good fire, A
silk handkerchief is auseful adjunct to the machine,
The glass plate should be wiped quite free from dirt,
and the glass support of the conductor must also be wiped,
the handkerchief being made very hot. The rubbers must
be taken off (if constructed so as to be movable, as de-
scribed), and placed before the fire till quite hot. Their
powers may be enormously increased by covering them with
amalgam, as sold in the electrical shops, but a far better
plan is to cover the cushions with tinfoil, which can be glued
right round the rubbers and over the backs. This will need
renewing at interyals, a3 the plate in turning wears it out.
Now, when the rubbers are quite hot and all the glass of
_the machine is dry and hot (this is necessary, because, if
damp, the electricity would escape without producing any
effect), the rubbers are put into their proper places on each
side of the glass, and on turning the handle (which will be
rendered easier ifthe machine is firmly clamped to the table)
and approaching the knuckle-to the conductor, a succession
of brilliant sparks will be emitted from the conductor. If
this does not happen either the glass or some part of the
machine is damp, or the machine is not put together quite
correctly, and must be examined to find out the faalt.
A machine of the size described should give a spark an
Inch long when working properly. A great number of ex-
periments may be performed with this machine with appar-