hread might be
wound round a spool. One end of the inductance is connected
permanently with the ground and from the other end two movable wires
go out, one of which can be connected with the spark gap and the other
with the antenna that goes into the air and catches the sound waves.
There isn't anything very terrible about that, you see."

"Antenna is what butterflies have," suggested Nancy vaguely.

"Quite right!" assented the wireless man. "Only radio antennae are not
to feel with--at least not in the same way. Nevertheless they do reach
out and capture the sound. On all wireless stations you will notice
the masts that support them. Sometimes there is one wire, sometimes a
group. It is the wires themselves, remember, not the masts, which are
the antennae. Nowadays, however, you will occasionally see an indoor
aerial used in connection with small, low-power outfits. It does away
with the masts and outside equipment and frequently serves the same
purpose quite satisfactorily. But most persons prefer the older method
and for long-distance work it has, up to date proved to be
indispensable. Now the antenna has both electrical capacity and
inductance, and when connected up with the apparatus a wireless
operator can at will cause it to disturb the magnetic fields
surrounding the earth."

"You didn't say how high these masts had to be, Bob," put in Mr.
Crowninshield. "Are they always the same length?"

"Oh, no, indeed, sir," was the prompt response. "Their length varies
according to the type of service required of them. I'm glad you asked
the question. Sometimes the masts are about two hundred feet high;
again they may approximate four hundred and eighteen feet. And
sometimes in emergencies you will discover no masts at all, the wires
being fastened instead to captive balloons or kites which hold them in
place long enough to send or receive hasty messages. This latter
method is usually resorted to in wartime or during army or navy
maneuvers. There are also compact radio sets to be had that can be
carried on mule-back and set up and taken down on a hurried army
march. On shipboard the ordinary masts of the vessel serve, of
course, to support the antenna."

"Thank you, Bob. That is exactly what I wanted to know," said Mr.
Crowninshield.

"I'm glad, sir. Now you'd think by this time we had everything
necessary to produce our wireless waves and yet we haven't. There is
still one thing almost more important than all the r