LIFE-SAVING SERVICE SIGNALS 249
and synchronised with a submarine sound signal, distance^ as well as
bearing can be determined.
The Reiolmng Beam Station (12) consists of the emission on short
wave-lengths of wireless signals projected in a narrow beam, a different
Morse letter signal being transmitted for each point and half-point of
the compass The navigator listens by means of a special type of
wireless receiver (independent of the ordinary WIT installation) and
hears a series of five or more Morse letters, transmitted at a uniform
speed, as the revolving beam intersects the ship's course. The middle
letter of the series indicates the exact bearing of the ship (derived from
a special chart giving the lettered sectors) in relation to her course. By
repeating the observations at short intervals and co-ordinating the
results with the ship's course and speed, the exact position of the ship
can be determined.
The Rotating Beacon or Loop Station (13) consists of a medium
wave wireless beam transmitter rotating at a uniform speed. A con-
tinuous signal is transmitted with special code signals as the beam
passes certain points of the compass These signals are received on a
standard wireless receiver, and as the beam rotates the signal strength
rises and falls being at a minimum as the beam passes the ship. As the
speed of the rotation of the beam, is known, the bearing of the station
can be calculated by measuring the time interval between the beam
passing a known point of the compass (indicated by the transmission
of the code signal referred to above) and passing the ship (indicated by
the minimum strength of signal)
II. VISUAL AND SOUND SIGNALS.
Signals used in connection with the Life-Saving Services on the Coasts
of Great Britain and Northern Ireland.
Signal. Signification,
(a) Signals to Vessels in Distress
Rocket throwing white (stars, or Distress signal or plight
white flare, observed — Assistance
summoned.
One explosive sound signal showing Distress signal or plight
bright white star on bursting. observed — Life-Saving
Apparatus called out.
Two explosive sound signals, show- Distress signal or plight
hag bright green stars on bursting. observed — Lifeboat
called out-