, full length of iron core,
and 3/4 in. in diameter.
Procure a bundle of small iron wire, say 1/4 in. in diameter, and
cut it 3-1/2 in. long; bind neatly with coarse thread and file the
ends smooth (Fig. 1). This done, make two wood ends, 1-1/4 by
1-1/4 in. and 3/8 in. thick, and varnish. Bore holes in the center
of each so the core will fit in snugly and leave about 1/4 in.
projecting from each end (Fig. 1).
After finishing the core, shellac two layers of thick paper over
it between the ends; let this dry thoroughly. Wind two layers of
bell magnet wire over this, allowing several inches of free wire
to come through a hole in the end. Cover with paper and shellac as
before. Wind about 1/8 in. of fine wire, such
[Illustration: Medical Induction Coil]
as used on telephone generators, around the coil, leaving long
terminals. Soak the whole in melted paraffin and let cool; bind
tightly with black silk.
The vibrator is made of a piece of thin tin to which is soldered
the head of an iron screw and on the other side a small piece of
platinum, which can be taken from an old electric bell (Fig.
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