ed magnet wire, the ends of which may be passed
through small holes in the wooden ends. If a drill small enough is
not available, the holes may be made with a hot knitting needle or
a piece of wire heated to redness. After the primary coil is wound
it should be thoroughly insulated before winding the secondary.
This may be done by wrapping with 4 or 5 thicknesses of paper.

The secondary coil should be wound with single covered wire,
preferably silk-covered, although cotton will do. The more turns
there are on the secondary the higher the voltage will be, so the
wire used must be fine. Number 32 to 36 will give good results,
the latter giving more voltage but less amperage. Each layer of
the secondary winding should be insulated from the others by a
piece of thin paraffined paper wrapped over each layer as it is
finished. It is well not to wind to the extreme ends of the paper
insulations, but to leave a space of about 1/8-in. at each end of
the winding to prevent the wires of one layer slipping over the
ends of the paraffin

[Illustration: Induction Coil]

paper and coming in contact with the layer beneath, thus causing a
short circuit. The secondary winding should have at least a dozen
layers and should be carefully wound to prevent short circuiting.

In order to reduce the strength of the current a piece of brass
tubing, F, is pushed into the space, C, surrounding the core, or
if no brass tubing of the required size is on hand, roll a paper
tube, cover with 4 or 5 thicknesses of tinfoil and then wrap with
more paper, using glue to hold the tinfoil in place and to keep
the tube from unwinding. When the tube is pushed all the way in,
the current produced

[Illustration: Induction Coil]

will be almost unnoticeable, but when it is withdrawn the current
will be so strong that a person cannot let go the handles until
the coil is shut off. After the secondary coil is wound it should
be covered with stiff paper, and the whole coil, including the
wood ends, should then be enameled black.

It is then ready to be mounted on a wooden base as shown in Fig.
2. The secondary terminals are connected to the binding-posts, AA,
which may be fastened on the base if desired. One wire from the
primary is connected with the binding-post, B, and the other is
connected with the armature, D, which may be taken from an old
electric bell. The contact screw, E, also from an electric bell,
is connected to the binding-post, C. The conta