t is that our ears do not hear all the sounds that go on about
us. The merciful Lord has arranged that when there are less than
twenty-four vibrations a second, or more than forty thousand they
escape us. But a wireless instrument, on the contrary is spared
nothing, having attached to it a detector that catches every sound and
an amplifier that magnifies it and makes it discernible to our ears.
When you listen in on a wireless telephone you will be uncontestably
conscious of this. Also you must take into consideration that the
waves sent out by a radio transmitter are not choppy, irregular ones
such as you get when a stone is tossed into the water; wireless waves
go out in regular, well-formed relays that neither overlap nor obscure
one another. Were this not so the signals made would be jumbled
together and utterly unintelligible."

"Sure they would!" Bob's young brother nodded.

"Now to insure these several results we are compelled to resort to the
help of scientific apparatus. Therefore at every receiving station we
have devices that will intercept the waves as they come in;
retransform them into electrical oscillations; and catching the weak
oscillations make them strong enough to be read. Hence we use some
type of induction coil by means of which a battery current of such low
pressure and diffused flow as scarcely to be felt will be transformed
or concentrated into a pressure that is very powerful. In order to
form wireless waves we must have a frequency of at least one hundred
thousand vibrations a second; and as it is out of the question to
produce these by mechanical means we employ a group of Leyden jars.
Such jars you have of course seen. They have in them two pieces of
tinfoil separated by glass, which is a nonconductor of electric
currents, and various other acids and minerals. When you connect a
number of these small jars together you have a battery as powerful as
that of a large single jar."

"I never saw jars like those," objected Dick.

Bob beamed at the intelligence of the demurrer.

"When I say jar," explained he, "it does not necessarily mean that
these jars are of the round, cylindrical shape that comes to mind when
you mention the word; on the contrary Leyden jars are often flat
because such a form makes them more compact. That is also why we use
several little ones instead of one big one. But whatever their shape
the principle involved is always the same. When the terminals are
connected with