Anything may be used for signalling, that appears and
disappears, like a lantern, or an opened and closed umbrella, or that
moves, as a waved flag or a person walking to and fro on the crest of a
hill against the sky. Sound also can be employed, as long and short
whistles. Their use can be thoroughly taught in two hours, and however
small the practice of the operators, communication, though slow, is
fairly accurate, while in practised hands its rapidity is astonishing.
The proportion of time occupied by the flashes and intervals is as
follows. (I extract all the rest of the article from the pamphlet
published by the inventors of the system.)
Flashing Signals, with Flags.--Supposing the short flash to be half a
second in duration, the long flash should be fully a second and a half.
The interval between the flashes forming a figure should be equal to a
short flash, and the interval between two figures should be equal to a
long flash. After the last figure of the signal is finished, there should
be a pause equal to at least one-third of the time taken up by the
figures. After this pause, the signal should be again repeated with the
same measured flashes and intervals, and so continued until answered by
all to whom it is addressed.
[Example of Morse code].
Care must be taken never to commence a fresh signal before the answers to
the last have ceased; and signals are never to be answered until their
repetitions have been observed a sufficient number of times to make an
error impossible.
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