_receiver_, or, more properly, the _receptor_. The aerial wire is
precisely the same for either wireless telegraphy or wireless
telephony. The transmitter of a wireless telegraph set generally uses
a _spark gap_ for setting up the electric oscillations, while usually
for wireless telephony a _vacuum tube_ is employed for this purpose.
The receptor for wireless telegraphy and telephony is the same and may
include either a _crystal detector_ or a _vacuum tube detector_, as
will be explained presently.

The Easiest Way to Start.--First of all you must obtain a government
license to operate a sending set, but you do not need a license to put
up and use a receiving set, though you are required by law to keep
secret any messages which you may overhear. Since no license is needed
for a receiving set the easiest way to break into the wireless game is
to put up an aerial and hook up a receiving set to it; you can then
listen-in and hear what is going on in the all-pervading ether around
you, and you will soon find enough to make things highly entertaining.

Nearly all the big wireless companies have great stations fitted with
powerful telephone transmitters and at given hours of the day and
night they send out songs by popular singers, dance music by jazz
orchestras, fashion talks by and for the ladies, agricultural reports,
government weather forecasts and other interesting features. Then by
simply shifting the slide on your tuning coil you can often tune-in
someone who is sending _Morse_, that is, messages in the dot and dash
code, or, perhaps a friend who has a wireless telephone transmitter
and is talking. Of course, if you want to _talk back_ you must have a
wireless transmitter, either telegraphic or telephonic, and this is a
much more expensive part of the apparatus than the receptor, both in
its initial cost and in its operation. A wireless telegraph