Colomb and Bolton's flashing signals, adopted in our Army and Navy, and
used in many other countries as well, are eminently suited to the wants
of an expedition. 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.
[Fig. 1 and Fig 2--sketch of signalling with flags as described below].
The signalman may work from left to right, or from right to left, as
shown in figs. 1 and 2, according to convenience and the direction of the
wind. To make a short flash, the flag is waved from a to b, and back to
the normal position a. To make a long flash, the flag is waved from a to
c, and back to the normal position a.
The numerals 1 to 5 are, therefore, denoted by one to five waves of the
flag from a to b, recovering to a.
The numeral 6 by a wave from a to c, recovering to a. The numeral 7 by a
wave from a to b, back to a, and then to c, recovering to the normal
position a. The numeral 8 is denoted by a wave from a to c, back to a,
and then to b, recovering to the normal position a. The numeral 9 is
denoted by two waves from a to b, and one from a to c. The numeral 0 by
one wave from a to c, recovering again to a, and then two waves from a to
b. The other signs are made in the same manner, so that a short motion
shall always represent a short flash, and a long motion a long flash.
On the completion of the motions required for each sign, the flag must
always be brought to the position a. When the word, or group of figures,
is completed, the flag may be lowered in front of the body.
In receiving a message, the flag should always be kept in the position a,
except when answering.
In waving the flag, the point of the staff should be made to describe a
figure of 8 in the air to keep the flag clear.
Each signal party must consist of not less than two men, whose duties
will be as follows:--
In receiving messages: No. 1 works the flag for answering, etc., and
refers to the code for the interpretation of the numbers received, and
calls out the words to No. 2. No. 2 fixes the telescope and reads from
the distant station, calling out the numbers as they are made for the
information of No. 1, and writes down the numbers and meaning thereof.
Suppose station "A" in communication with station "B":--No. 1 at "A" on
being told by No. 2 that "B" is about to send a message, takes up his
position at attention, holding the flag over the left arm and under the
right, or vice versa across his body, according to the wind, with the
code book in his hand. No. 2 fixes his eyes on the glass, and on
receiving the numbers from "B" calls them out to No. 1, who ascertains
their meaning from the code, and gives the words to No. 2, who writes
them down in his book, and then placing his eye to the glass, tells No. 1
to make the answer. No. 2 does not, however, direct the answer to be made
until he is sure of the correctness of the signal received.
Flashing Alphabet, for Use without a Code.--The following alphabet,
etc., can be used under circumstances when it is not convenient or
possible to have recourse to the Signal Book, and forms in itself a
perfect telegraphic system, necessarily somewhat slow in its application,
but having the great advantage of requiring very little previous
knowledge and practice to work with correctness. The symbols and numbers
expressing the alphabet are identical with those forming the alphabet in
the Signal Book.
[Chart with code signals].
All particulars as to the machines and lanterns used in the Service, for
making these flashing signals, and the code, can be procured at W. Nunn and
Co.'s Army and Navy Lamp and Signal Works, 65, George Street East,
London, E.
Reflecting the Sun with a Mirror.--To attract the notice of a division
of your party, five or even ten miles off, glitter a bit of looking-glass
in the sun, throwing its flash towards where you expect them to be. It is
quite astonishing at how great a distance the gleam of the glass will
catch the sharp eyes of a bushman who has learnt to know what it is. It
is now a common signal in the North American prairies. (Sullivan.) It
should be recollected that a passing flash has far less briliancy than
one that dwells for an appreciable time on the retina of the observer;
therefore the signaller should do all he can to steady his aim. I find
the steadiest way of holding the mirror is to rest the hand firmly
against the forehead, and to keep the eyes continually fixed upon the
same distant object. The glare of the sun that is reflected from each
point of the surface of a mirror forms a cone of light whose vertical
angle is constant, and equal to that subtended by the sun. Hence when a
flash is sent to a distant place, the size of the mirror is of no
appreciable importance in affecting the size of the area over which the
flash is visible. That area is the section of the fasciculus of cones
that proceed from each point of the mirror, which, in the case we have
supposed, differs immaterially from the cone reflected from a single
point. Hence, if a man watches the play of the flash from his mirror upon
a very near object, it will appear to him of the shape and size of the
mirror; but as he retreats from the object, the edges of the flash become
rounded, and very soon the flash appears a perfect circle, of precisely
the same apparent diameter as the disc of the sun: it will, in short,
look just like a very faint sun. The signaller has to cause this disc of
light to cover the person whose notice he wishes to attract. I will
proceed to show how he can do so; but in the mean time it will be evident
that a pretty careful aim is requisite, or he will fail in his object.
The steadiness of his aim must be just twice as accurate, neither more
nor less, as would suffice to point a rifle at the sun when it was
sufficiently obscured by a cloud to bear being looked at: for the object
of the aim is of the same apparent size, but a movement of a mirror
causes the ray reflected from it to move through a double angle.
The power of these sun-signals is extraordinarily great. The result of
several experiments that I made in England showed that the smallest
mirror visible under atmospheric conditions such that the signaller's
station was discernible, but dim, subtended an angle of only one-tenth of
a second of a degree. It is very important that the mirror should be of
truly plane and parallel glass, such as instrument-makers procure; the
index glass of a full-sized sextant is very suitable for this purpose:
there is a loss of power when there is any imperfection in the glass. A
plane mirror only three inches across, reflects as much of the sun as a
globe of 120 feet diameter; it looks like a dazzling star at ten miles'
distance.
To direct the flash of the Mirror.--There are makeshift ways of
directing the flash of the mirror; as, by observing its play on an object
some paces off, nearly in line with the station it is wished to
communicate with. In doing this, two cautions are requisite: first, the
distance of the object must be so large compared to the diameter of the
mirror that the play of the flash shall appear truly circular and exactly
like a faint sun (see preceding paragraph): secondly, be careful to bring
the eye to the very edge of the mirror; there should be as little
"dispart" as possible, as artillerymen would say. Unless these cautions
be attended to very strictly, the flash will never be seen at the distant
station.
[Sketch of arrangement as described below].
An object, in reality of a white colour but apparently dark, owing to its
being shaded, shows the play of a mirror's flash better than any other.
The play of a flash, sent through an open window, on the walls of a room,
can be seen at upwards of 100 yards. It is a good object by which to
adjust my hand heliostat, which I describe below. Two bits of paper and a
couple of sticks, arranged as in the drawing, serve pretty well to direct
a flash. Sight the distant object through the holes in the two bits of
paper, A and B, at the ends of the horizontal stick; and when you are
satisfied that the stick is properly adjusted and quite steady, take your
mirror and throw the shadow of A upon B, and further endeavour to throw
the white speck in the shadow of A, corresponding to its pin-hole in it,
through the centre of the hole in B. Every now and then lay the mirror
aside, and bend down to see that A B continues to be properly adjusted.
Hand Heliostat.--Some years ago, I took great pains to contrive a
convenient pocket instrument, by which a traveller should be able to
signal with the sun, and direct his flash with certainty, in whatever
direction he desired. I did so in the belief that a signalling power of
extraordinary intensity could thus be made use of; and, I am glad to say,
I succeeded in my attempt. I at last obtained a pretty pocket instrument,
the design of which I placed in the hands of Messrs. Troughton and Simms;
and upon the earlier models of which I read a paper before the British
Association in 1858. I called it a "hand heliostat." I always carry one
when I travel, for it is a continual source of amusement. The instrument
is shown in fig. 1 (p. 280), and its principle is illustrated by fig. 2.
The scale is about 2/3.
E is the eye of the signaller; M the mirror; and L, S, fig. 2, a tube
containing at one end, L, a lens, and at the other, S, a screen of white
porcelain or unpolished ivory, placed at the exact solar focus of L: a
shade, K, with two holes in it, is placed before L. Let R, r, be portions
of a large pencil of parallel rays, proceeding from any one point on the
sun's surface, and reflected from the mirror, as R' r' (fig. 2). R'
impinges upon the lens, L, through one of the holes in K, and R' goes
free toward some distant point, O. Those that impinge on the lens will be
brought to a focus on S, where a bright speck of light might be seen.
This speck radiates light in all direction; some of the rays, proceeding
from it, impinge on the lens at the other hole in the shade K, as shown
in fig. 2, and are reduced by its agency to parallelism with r' and R',
that is, with the rays that originally left the mirror: consequently E,
looking partly at the edge of the lens, and partly into space, sees a
bright speck of light in the former, coincident with the point O in the
latter.
[Fig 1 and Fig 2, as described in the text].
What is true for one point in the sun's disc, is true for every point in
it. Accordingly, the signaller sees an image of the sun, and not a mere
speck of light, in the lens; and the part of the landscape which that
image appears to overlay, is precisely that part of it over which the
flash from his mirror extends; or, in other words, it is that from any
point of which a distant spectator may see some part or other of the
sun's disc reflected in the mirror. There is no difficulty in signalling
when the sun is far behind the back, if the eye-tubes are made to pull
out to a total length of five inches, otherwise the shadow of the head
interferes. For want of space, the drawing represents the tubes as only
partly drawn out. The instrument is perfectly easy to manage, and letters
can be signalled by flashes. Its power is perfectly marvellous. On a day
so hazy that colours on the largest scale--such as green fields and white
houses--are barely distinguishable at seven miles' distance, a
looking-glass no larger than the finger-nail transmits its signals
clearly visible to the naked eye.
I have made a makeshift arrangement on the principle of my heliostat,
using the object glass of an opera-glass for the lens, and an ordinary
looking-glass: the great size and short focus of the object glass is a
great convenience when using a mirror with a wide frame.
Professor W. H. Miller, the Foreign Secretary of the Royal Society, has
since invented a yet more compact method of directing the flash, which he
has described in the Proceedings of the Royal Society for 1865. It
consists of a plate of silvered glass, one of whose rectangular corners
is accurately ground and polished. On looking into the corner when the
glass is properly held an image of the sun is seen, which overlays the
actual flash. Beautifully simple as this instrument is, I do not like it
so much as my own, for the very fact of its requiring no "setting" is its
drawback. With mine, when the image of the sun is lost it is immediately
found again by simply rotating the instrument on its axis; but with
Professor Miller's the image must be felt for wholly anew.
Fire Signals.--Fire-beacons, hanging up a lantern, or setting fire to an
old nest high up in a tree, serve as night-signals; but they are never to
be depended on without previous concert, as bushes and undulations of the
ground will often hide them entirely. The sparks from a well-struck flint
and steel can be seen for much more than a mile.
Smoke Signals.--The smoke of fires is seen very far by day; and green
wood and rotten wood make the most smoke. It is best to make two fires
100 yards apart, lest your signalling should be mistaken for an ordinary
fire in the bush. These double fires are a very common signal to vessels
in the offing, on the African coast.
Other Signals.--By Sight.--A common signal for a distant scout is, that
he should ride or walk round and round in a circle from right to left, or
else in one from left to right.
Mr. Parkyns, speaking of Abyssinia, describes the habits of a caste of
robbers in the following words:--"At other times they will lie concealed
near a road, with scouts in every direction on the look-out; yet no one
venturing to speak, but only making known by signs what he may have to
communicate to his companions or leader. Thus he will point to his ear
and foot on hearing footsteps, to his eyes on seeing persons approach, or
to his tongue if voices be audible; and will also indicate on his fingers
the numbers of those coming, describing also many particulars as to how
many porters, beasts of burden or for riding, there may be with the
party."
A kite has been suggested as a day signal; and also a kite with some kind
of squib, let off by a slow-light and attached to its tail, as one by
night. (Colonel Jackson.)
Sound.--Whistling through the fingers can be heard at considerable
distances: the accomplishment should be learnt. Cooing in the Australian
fashion, or jvdling in that of the Swiss, are both of them heard a long
way. The united holloa of many voices, is heard much further than
separate cries. The cracking of a whip has a very penetrating sound.
Smells.--An abominable smell arrests the attention at night.
Letters carried by Animals.--In short reconnoitring expeditions made by a
small detachment from a party, the cattle or dogs are often wild, and run
home to their comrades on the first opportunity; in the event of not
being able to watch them, owing to accident or other cause, advantage may
be taken of their restlessness, by tying a note to one of their necks,
and letting them go and serve as postmen, or rather as carrier-pigeons.