contact, but for sharp tuning you need a _loose coupled tuning coil_.
Where a single coil tuner is used a _fixed_ condenser should be
connected around the telephone receivers. Where a loose coupled tuner
is employed you should have a variable condenser connected across the
_closed oscillation circuit_ and a _fixed condenser_ across the
telephone receivers.

When listening-in to distant stations the energy of the received
wireless waves is often so very feeble that in order to hear
distinctly an _amplifier_ must be used. To amplify the incoming sounds
a vacuum tube made like a detector is used and sometimes as many as
half-a-dozen of these tubes are connected in the receiving circuit, or
in _cascade_, as it is called, when the sounds are _amplified_, that
is magnified, many hundreds of times.

The telephone receiver of a receiving set is equally as important as
the detector. A single receiver can be used but a pair of receivers
connected with a head-band gives far better results. Then again the
higher the resistance of the receivers the more sensitive they often
are and those wound to as high a resistance as 3,200 ohms are made for
use with the best sets. To make the incoming signals, conversation or
music, audible to a room full of people instead of to just yourself
you must use what is called a _loud speaker_. In its simplest form
this consists of a metal cone like a megaphone to which is fitted a
telephone receiver.

About Transmitting Stations--Getting Your License.--If you are going
to install a wireless sending apparatus, either telegraphic or
telephonic, you will have to secure a government license for which no
fee or charge of any kind is made. There are three classes of licenses