back which is exactly what we illustrated by our experiment
with the two violins. If two strings are in tune and one is
caused to vibrate, the second will sound back and is in resonance.
So, when a Radio receiver is tuned to a certain station,
it is also said to be in resonance with that station.
    
Coming back to Radio, let us imagine that the transmitting
station is violin number 1 and the receiving set is violin number
2. If our set is in resonance tuned with the transmitting
station, we will hear its signals--if we are not in resonance we
naturally don't get the station.
    
We know that to tune a receiver it is necessary to turn one
or more dials on the panel of the set, but just what goes on in
the set when the position of the dial is changed, and what principles
make it possible to tune in one station and all others out,
is a matter that must be kept until a little later. However, by
this time you should have a clear idea of what is meant by tuning
and have a clear understanding of simple waves--water,
sound, and also--Radio waves--as far as possible in this first
lesson, which after all is just an introduction to Radio. In later
lessons we shall meet the acquaintances we made in this lesson
and learn to know them much better. We shall see how we can
vary the amplitudes of simple Radio waves and how this will
allow us to combine sound waves with the Radio waves.
FROM TRANSMITTER TO RECEIVER
    
Having considered the natural phenomena that make Radio
possible, we are now ready to look at our receiving apparatus
for a few moments. You may wonder why we don't start with
the details of the transmitting apparatus, but there are several
reasons why it is much better to start at the other end. In the
first place, receiving apparatus is much simpler than that of
transmitting. In the second place, there are many more receivers
in operation than transmitters, and much more chance
to see them and get on our road of repairing and servicing
receivers. And last of all, after you understand the receiver it
will be easy to start work on the transmitter and get a thorough
understanding of it in short order.
    
You know that the Radio wave is sent across, transmitted
from the transmitter, to the receiver through the ether. Remember
that ether forms a part of everything in nature--that is why
Radio waves travel everywhere, through houses, through the
earth, through the air.