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