1, and the block
fastened to the under side of the table, the apparatus is ready
for use, and has only to be connected to an ordinary telephone
transmitter and batteries as shown. The apparatus will work to a
certain extent even if the weight is removed, though not so clear.
** Wax Wood Screws [137]
Some workmen use tallow on lag or wood screws. Try beeswax for
this purpose. It is much cleaner to use and is just as good if not
better.
** How to Make an Induction Coil [138]
A small shocking coil, suitable for medical purposes, may be
constructed of materials found in nearly every amateur mechanic's
collection of odds and ends. The core, A, Fig. 1, is a piece of
round soft iron rod about 1/4 in. in diameter and about 4 in.
long. A strip of stiff paper about 3/4 in. wide is covered with
glue and wrapped around one end of the core, as shown at B, until
the diameter is about 3/8 in. The portion of the core remaining
uncovered is then wrapped with a piece of paper about 4 in. wide.
No glue is used on this piece, as it is removed later to form the
space, C, after the paper shell, D, has been wound upon it.
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