h the air he
can select the messages he wishes to read by sound.

You may wonder how one wireless operator gets into communication with
another. He first listens in to determine whether messages are coming
through the ether within range in the wave-length he is to use.
Hearing nothing, he adjusts his sending apparatus to the desired
wave-length and switches this in with the signal aerial which
serves both his sending and his receiving set. This at the same time
disconnects his receiving set. He sends out the call letters of the
station to which he wishes to send a message, following them with
his own call letters, as a signature to show who is calling. After
repeating these signals several times he switches out his sending set
and listens in with his receiving set. If he then gets an answer from
the other station he can begin sending the message.

Marconi was not allowed to hold the wireless field unmolested.
Many others set up wireless stations, some of them infringing upon
Marconi's patents. Others have devised wireless systems along
more original lines. Particularly we should mention two American
experimenters, Dr. de Forest and Professor Fessenden. Both have
established wireless systems with no little promise. The system of
Professor Fessenden is especially unique and original and may be
destined to work a revolution in the methods of wireless telegraphy.

With an increase in the number of wireless stations and varieties
of apparatus came a wide increase in the uses to which wireless
telegraphy was applied. We have already noticed the press service
from Poldhu. The British Government makes use of this same station to
furnish daily news to its representatives in all parts of the
world. The wireless is also used to transmit the time from the great
observatories.

Some of the railroads in the United States have equipped their trails
as well as their stations with wireless sets. It has proved its worth
in communicating between stations, taking the place in time of need
of either the telegraph or the telephone. In equipping the trains with
sets a difficulty was met in arranging the aerials. It is, of course,
impossible to arrange the wires at any height above the cars, since
they would be swept away in passing under bridges. Even with very low
aerials, however, communication has been successfully maintained at
a distance of over a hundred miles. The speed of the fastest train
affects the sending and receiving of mes