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inch between them, the filings will about half fill the

The filings must be very carefully prepared, and in order
to make them, first use a. coarse-grained file on the edge
of a five-cent piece. Do not use the fine dust and powder,
but only the fairly coarse filings. Mix a few silver filings
from a ten-cent piece with the nickel in such proportion
that the mixture is 90% nickel and 10% silver.

You will have to experiment - considerably to find out
just the right
a m o u n t o f
filings to place
in the tube,
and how far
apart to place
the brass rods

«all! [Ill-[1‘]!








FIG. 234. —Details of the Coherer. or plugs°
Remove the

gong from an old electric bell and mount the bell on the
base as shown in Figure 2 3 3. It should be in such a posi-
tion that the bell hammer will touch the coherer very
lightly when the bell is ringing.

The two binding-posts, tube, rods, and filings constitute
the coherer. The bell is the decoherer. '

The next thing required in order to complete the appara-
tus is a relay. You may use the relay described in Chapter
X or build one according to the plan shown in Figure 235.
This relay consists of a single electro-magnet mounted


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