Masters of Space - Morse, Thompson, Bell, Marconi, Carty | Page 6

system is also used by the Army.
The perfection of wireless telegraphy has caused the Ardois and other
signal systems depending upon sight or sound to be discarded in all but
exceptional cases. The wig-wag and similar systems will probably
never be entirely displaced by even such superior systems as wireless
telegraphy. The advantage of the wig-wag lies in the fact that no
apparatus is necessary and communication may thus be established for
short distances almost instantly. Its disadvantages are lack of speed,
impenetrability to dust, smoke, and fog, and the short ranges over
which it may be operated.
There is another form of sound-signaling which, though it has been

developed in recent years, may properly be mentioned in connection
with earlier signal systems of similar nature. This is the submarine
signal. We have noted that much attention was paid to communication
by sound-waves through the medium of the air from the earliest times.
It was not until the closing years of the past century, however, that the
superior possibilities of water as a conveyer of sound were recognized.
Arthur J. Mundy, of Boston, happened to be on an American steamer
on the Mississippi River in the vicinity of New Orleans. It was rumored
that a Spanish torpedo-boat had evaded the United States war vessels
and made its way up the great river. The general alarm and the
impossibility of detecting the approach of another vessel set Mundy
thinking. It seemed to him that there should be some way of
communicating through the water and of listening for sounds
underwater. He recalled his boyhood experiments in the old
swimming-hole. He remembered how distinctly the sound of stones
cracked together carried to one whose ears were beneath the surface.
Thus the idea of underwater signaling was born.
Mundy communicated this idea to Elisha Gray, and the two, working
together, evolved a successful submarine signal system. It was on the
last day of the nineteenth century that they were able to put their
experiments into practical working form. Through a well in the center
of the ship they suspended an eight-hundred-pound bell twenty feet
beneath the surface of the sea. A receiving apparatus was located three
miles distant, which consisted simply of an ear-trumpet connected to a
gas-pipe lowered into the sea. The lower end of the pipe was sealed
with a diaphragm of tin. When submerged six feet beneath the surface
the strokes of the bell could be heard. Then a special electrical receiver
of extreme sensitiveness, known as a microphone, was substituted and
connected at the receiving station with an ordinary telephone receiver.
With this receiving apparatus the strokes of the bell could be heard at a
distance of over ten miles.
This system has had a wide practical application for communication
both between ship and ship and between ship and shore. Most
transatlantic ships are now equipped with such a system. The
transmitter consists of a large bell which is actuated either by
compressed air or by an electro-magnetic system. This is so arranged
that it may be suspended over the side of the ship and lowered well

beneath the surface of the water. The receivers consist of microphones,
one on each side of the ship. The telephone receivers connected to the
two microphones are mounted close together on an instrument board on
the bridge of the ship. The two instruments are used when it is desired
to determine the direction from which the signals come. If the sound is
stronger in the 'phone on the right-hand side of the ship the commander
knows that the signals are coming from that direction. If the signals are
from a ship in distress he may proceed toward it by turning his vessel
until the sound of the signal-bell is equal in the two receivers. The
ability to determine the direction from which the signal comes is
especially valuable in navigating difficult channels in foggy weather.
Signal-bells are located near lighthouses and dangerous reefs. Each
calls its own number, and the vessel's commander may thus avoid
obstructions and guide the ship safely into the harbor. The submarine
signal is equally useful in enabling vessels to avoid collision in fogs.
Because water conducts sound much better than air, submarine signals
are far better than the fog-horn or whistles.
The submarine signal system has also been applied to submarine
war-ships. By this means alone may a submarine communicate with
another, with a vessel on the surface, or with a shore station.
An important and interesting adaptation of the marine signal was made
to meet the submarine warfare of the great European conflict. At first it
seemed that battle-ship and merchantman could find no way to locate
the approach of an enemy submarine. But it was found that by means of
the receiving apparatus of the submarine