ire. At one side secure
two receptacles, B B, and one single post switch, C. Place another
switch at I and another binding-post at F. The oven is now ready
to be connected.

Withdraw the wooden core from the coils of wire and secure the
latter by bands of tin to the board. Connect the ends of the wire
to binding-posts E and F, as shown. From the other set of
binding-posts, E, run a No. 12 or No. 14 wire, connecting lamp
receptacles, B B, and switch, C, in parallel. Connect these three
to switch, D, in series with binding-post, F, the terminal of the
coil. Place 16-cp. lights in the receptacles and connect the fuses
with a 110-volt lighting circuit. The apparatus is now ready for
operation. Turn on switch, D, and the lamps, while C is open. The
coil will commence to become warm, soon drying out the
plaster-of-paris. To obtain more heat

[Illustration: Electric Furnace]

open one lamp, and to obtain still more open the other and close
switch C.
--Contributed by Eugene Tuttles, Jr., Newark, Ohio.

** How to Make an Ammeter [49]

Every amateur mechanic who performs electrical experiments will
find use for an ammeter, and for the benefit of those who wish to
construct such an instrument the following description is given:
The operative principle

[Illustration: Complete Ammeter and Details]

of this instrument is the same as that of a galvanometer, except
that its working position is not confined to the magnetic
meridian. This is accomplished by making the needle revolve in a
vertical instead of a horizontal plane. The only adjustment
necessary is that of leveling, which is accomplished by turning
the thumbscrew shown at A, Fig. 1, until the hand points to zero
on the scale.

First make a support, Fig. 2, by bending a piece of sheet brass to
the shape indicated and tapping for the screws CC. These should
have hollow ends, as shown, for the purpose of receiving the
pivoted axle which supports the hand. The core, Fig. 3, is made of
iron. It is 1 in. long, 1/4 in. wide and 1/8 in. thick. At a point
a little above the center, drill a hole as shown at H, and through
this hole drive a piece of knitting-needle about 1/2 in. long, or
long enough to reach between the two screws shown in Fig. 2. The
ends of this small axle should be ground pointed and should turn
easily in the cavities, as the sensitiveness of the instrument
depends on the ease with which this axle turns.

After assembling the core as shown in Fig.