al point of view, is as follows, referring to Figure 159:

The "A" battery heats the filament, causing a stream of electrically
charged particles to flow out from the filament in all directions.
These electrons act as a conductor, and close the circuit which
consists of the plate, the "B" battery, and the telephone receivers,
one end of this circuit being connected to one side of the filament
circuit. Current then flows from the positive terminal of the "B"
battery to the plate, then to the filament by means of the stream of
electrons emitted by the filament, along one side of the filament,
through the wire connected to the positive terminal of the "A" battery
to the telephone receivers, through the receivers to the negative
terminal of the "B" battery.

As long as the filament remains lighted a steady current flows through
the above circuit. The "grid" is connected to the aerial wire to
intercept the radio waves. These waves produce varying electrical
charges on the grid. Since the stream of charged particles emitted by
the filament must pass through the grid to reach the plate, the
charges which the radio waves produce on the grid strengthen or weaken
the stream of electrons emitted by the filament, and thus vary the
current flowing in the telephone receiver circuit. The changes in this
current cause the receiver diaphragm to vibrate, the vibrations
causing sounds to be heard. Since the variation in the telephone
receiver circuit is caused by electrical charges produced by the radio
waves, and since the radio waves change according to the sounds made
at the transmitting station, the variations in the telephone receiver
current produces the same sounds that are sent out at the transmitting
station. In this way concerts, speeches, etc., are reproduced in the
receivers.

The modern radio receiving set includes various devices, such as
variable condensers, variocouplers, loose-couplers, variometers, the
purpose of which is to "tune" or adjust the receiving set to be
capable of receiving the radio waves. An explanation of such devices
is not within the scope of this book, but there are numerous
reasonably priced books and pamphlets on the market which describes in
a simple manner all the component parts of a radio-receiving set.

From the foregoing remarks it is seen that a six-volt storage battery
is required with each receiving set which uses the audionbulb type
detector. The filament current of an audion-bulb averag