What is the Principle of the Wireless Telegraphy?
Drop a stone in a pool of water. Circular waves or ripples will travel
outward in all directions. That is the principle of wireless telegraph.
If a chip be floating on the water it will be rocked by each ripple,
just as a wireless receiving station will respond to the electrical
waves or impulses that make up a wireless message. It is not known
just how the invisible wireless waves are propelled through space,
but they travel through the ether in the air in very much the same
way as do sound waves. The electrical signals, too, are received only
by apparatus that is attuned to them; that is, they can not be heard
except at wireless stations, any more than sound can be heard by the
ears of a deaf person.
The wireless waves have a definite length, can be measured in feet or
meters, and are regulated according to the distance the message is to
travel. Stations that send a few hundred miles use a wave length of six
hundred meters, or less, while at the powerful land stations used for
trans-atlantic work the wave lengths used run into as many thousands.
Why Don’t the Messages Go to the Wrong Stations?
So that the hundreds of messages hurtling through space at the same
time will not interfere, the wireless stations are equipped with
tuning-apparatus through which they can adjust their wave length to
receive the particular message desired. A different wave length is
used by each ship or wireless shore station, and even though dozens of
messages fill the air, the minute the wireless operator adjusts his
tuner to the length of the station he is after, that particular message
stands out very strongly and all the others grow dim.
[Illustration: The Marconi Wireless station at Miami, Fla., which is
typical of the shore stations that handle messages to several thousand
ships at sea.]
How Does the Wireless Reach Ships at Sea?
All ships at sea report their positions regularly; thus it is a simple
matter for a shore station to send a wireless message to the ship to
which it is addressed. For example, the Marconi station at Sea Gate,
New York, wants to reach the Lusitania. The operator looks up that
vessel on the list and notes her call signal and wave length. He
adjusts his tuner to correspond and calls her signal, M F A, repeating
it three times.
The wireless man on the vessel, knowing that he is within range of a
shore station, has set his tuner at the wave length assigned to him and
is listening. When his call letters are heard, he acknowledges them
and signals to go ahead with the message. When it has been given, the
Sea Gate station “signs off” with its call letters W S E and the ship
operator enters in his record that that particular message reached him
via the Marconi station at Sea Gate. Thus, with the wide variety in
wave lengths, no confusion of messages exists and any desired ship or
shore station can be called, just as a direct telephone connection is
secured by giving the central station the call number of the subscriber
wanted.
What Kind of Signs Are Used in the Wireless?
The actual wireless message is composed of dots and dashes, which, in
certain combinations, stand for certain letters of the alphabet. This
is done through opening and closing the electrical circuit by pressing
a key, a sharp touch forming a dot and a longer pressure a dash, as
with the wire telegraph.
If secrecy in a wireless message is wanted, the words are sent in
cipher which, of course, cannot be understood by outsiders. The
Government sends thousands of words each day without a single word
meaning anything to the wireless stations that happen to be “listening
in.” While it is true that any one owning a wireless receiving set may
listen to messages flying through the air, every person within hearing
who understands the Morse Code can read the telegrams that come into a
telegraph office. Knowledge thus gained, however, is of little value,
as the law provided heavy penalties for disclosing the contents of any
kind of telegraph message.
What Does a Wireless Equipment Consist of?
The various apparatus that comprises a wireless equipment can not be
properly explained without the use of technical language, but the
general principle of operation is somewhat as follows: If a small loop
of copper wire, with a slight separation between the ends, is placed
across a room from an electric spark, it will be slightly affected.
Increase the electrical current to far greater power and control it,
and the invisible electrical wave may be thrown many miles. To send
a message across the ocean, the current used by the modern wireless
station is so powerful that it will pass through storm and fog,
even through mountains, without losing much of its force. When this
tremendous force is released by pressing the telegraph key, it leaps
from the aerial wires, or antennae, travels across the Atlantic and is
picked up by a corresponding aerial, attuned to receive the signal.
[Illustration: Pack and riding horses grouped together ready for
unloading the Marconi wireless set used in the cavalry.
Station set up and working.