e axle, and filed tapering so
the forging or hook E, on the trailer attachment, could be kept in
position. The washer F is held tightly against the hook by
pressure from a spring, G. The spring is held in place by a small
nut, H, and cotter pin, 1. This attachment makes a flexible joint
for turning corners. When turning from right to left the left hook
on the trailer fork stays in

[Illustration: Fig. 2-The Hook in Position]

position, while the right hook pushes the washer F outward and
relieves the strain on the fork. This attachment also makes it
easy to remove the trailer from the bicycle. The washers F are
pushed outward and the hook raised off the axle.
--Contributed by John F. Grieves, Providence, R. I.

** Home-Made Telephone Transmitter [398]

The parts for transmitting the sound are encased in a covering, H,
made from the gong of an old electric bell. A round button, D, is
turned or filed from the carbon electrode of an old

[Illustration: Telephone Transmitter]

dry cell and a hole drilled through the center to fit in a
binding-post taken from the same battery cell. This button must be
carefully insulated from the shell, H, by running the binding-post
through a piece of small rubber tube where it passes through the
hole and placing a rubber or paper washer, F, under the carbon
button, and an insulating washer under the nut on the outside.
This will provide one of the terminals of the instrument.
Construct a paper tube having the same diameter as the button and
with a length equal to the depth of the bell case, less 1/8 in.
Glue or paste this tube to the button so it will form a paper cup
with a carbon bottom.

The diaphragm, B, which is the essential part of the instrument,
should be made as carefully as possible from ferrotype tin,
commonly called tintype tin. Cut a circular piece from this metal
the exact size of the outside of the shell. A hole is made in the
center of the disk a little larger than a binding-post that is
taken from another old battery cell. When making the hole in the
disk be careful not to bend or crease the tin. Scrape the black
coating from the tin around the outside about 1/4 in. wide and a
place about 1 in. in diameter at the center.

The second electrode, C, is made the same as D, and fastened to
the tin diaphragm with the binding post without using any
insulation. A third binding post, G, is fastened to the shell
through a drilled hole to make the other terminal. The