est that we have
not yet spoken of."

"What's that, Bob?" piped Walter.

"The tuner. You recall that at the beginning I mentioned the pitch,
note, or key of the sound produced or received?"

"Yes," returned the class in chorus.

"Well, it is in that tune or pitch, or whatever you prefer to call it,
that a large measure of the secret of wireless lies. To be successful
in getting and sending messages we must tune the oscillations, or key
the signals caused by the discharge of the battery in our Leyden jar,
so that they will be in harmony (or at precisely the same pitch) with
the antenna circuit. That is, the parts of the instrument must
synchronize, just as two persons who would talk together must speak in
the same language. This adjustment is made in the inductance coil
because although both the Leyden jar where the spark is generated that
causes the oscillations and the antenna can be regulated independently
of each other a few turns of the inductance coil affects each circuit.
After the two circuits have been adjusted to the same frequency they
are said to synchronize. Often to reach this result a device is used
that states precisely the wave length, and after the frequency of one
circuit has been ascertained the other can easily be adjusted to
correspond with it. The length of the wave is, you see, dependent on
the largeness of the antenna and the capacity, or strength of current,
of the Leyden jar. Just as a child uses a big stone to produce the
largest splash and greatest waves so we must have a powerful force
behind our wave lengths to make them carry most successfully. In
accordance with this law, generally speaking, we find short wave
lengths used for low power, short-distance outfits; and long wave
lengths for high-power circuits whose aim is to traverse continents
and oceans."

Bob pushed back his chair.

"I think," said he, "we have now come to a good stopping place and we
will call the lesson off for to-day. If you digest all I have told
you, you will have had an ample radio starter."

"You haven't said much about sending messages," complained Dick.

"That is quite another story," smiled the boy's tutor, "and such a
long one that were I to tell it to you now it would mean you would get
no sailing or swimming to-day."

Instantly Dick was on his feet, Leyden jars and inductance coils
forgotten.

"We'll cut it out then," he laughed. "Who is for a swim? I'll race any
man to the bath-house!" And off