series of aluminum plates, some of which are movable and the rest
stationary.

Buy a small variable condenser. Its function is to tune the secondary
circuit, which is accomplished simply by turning the knob. Such a
condenser could not be made without the use of a good set of tools,
and the author strongly advises it be bought instead of made at home
in order to avoid trouble. The aluminum plates are spaced very closely
and great care should be taken to avoid bending them, as they must not
touch each other.

The aerial for this set should be about 60 to 100 feet in length and
as high and clear of surrounding objects as possible. A simple
porcelain cleat at either end, as shown in the drawing, will serve to
insulate it sufficiently.

Your ground connection can be made best by wiring to the cold water
pipe, although wiring to a steam or gas pipe will do almost as well.

You are now prepared to mount the various instruments in their proper
locations. For your table instruments, get a good pine board about
seven-eighths of an inch thick. Buy four binding posts and use one for
the aerial wire, one for the ground wire, and two for the phones or
head set.

To operate the set, first bring the hinged coil of wire close up to
the fixed coil and adjust the detector until you can hear in your
receivers the loudest click caused by the turning on and off of the
key to a nearby electric light. If no light is available, a buzzer and
dry battery should be used. When the detector is properly adjusted you