A means of communication by audible or visible signs between two distant points according to a preconcerted system.
The means of signaling are numerous.
Among them may be cited:—
| Balls. | Horns. |
| Bells. | Lanterns. |
| Bonfires. | Lights. |
| Electric sounders. | Rockets. |
| Flags. | Semaphores. |
| Guns. | Torpedoes. |
| Heliostats. | Whistles. |
Flags are very generally employed for signaling, being equally well adapted for land or sea service.
In the former case the various combinations are made by waving the flag to the right or left, or by holding it in a particular position.
Nautical signals are formed by the different arrangements and combinations of several flags and pennants of different colors; each of these indicates a number, corresponding to a phrase or sentence, which is entered in a book.
Every naval vessel is furnished with one of these books, by reference to which the number and signification of any combination displayed by another naval vessel of the same nation may be at once understood.
The particular system used is termed a code.
That of the
British navy is capable of expressing about 14.000 words and phrases.
Codes of more limited capability are employed in the merchant service.
Flashing-signals are made by intermittent flashes of lime light, of shorter or longer duration, so as to spell out a message.
Railway-signals are made for many purposes, usually to check speed or stop; but some signals indicate that the way is clear (see Railway-signal).
Fig. 5080 is a signal to be placed on curves, tunnels, or sidings.
An adjustable book on the cab of the locomotive strikes a trigger on a wayside post and sets a signal in advance.
Reconnoissances by signal-parties have been made by means of balloons on several occasions, the balloon in each case being
[
2177]
what is called
captive, that is, being held by a rope to limit the ascension and prevent its escape.
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Railway-signal. |
The first occasion was at the battle of
Fleurus, in 1794, when the
French used it to ascertain the position and evolutions of the Austrians.
It was fired at by the Austrians, but allowed to ascend out of range.
A captive balloon was again made use of by the
French at
Solferino, 1859.
A third use of balloons in this species of service was with the Army of the Potomac in the
Peninsular campaign, and perhaps in other fields of action.
The search for the lamented
Sir John Franklin gave rise to many ingenious schemes for signaling the party and giving them notice of succor.
Mr. Wallace's plan was to make a survey with the assistance of a captive balloon, affording a means of distributing notices which might reach the party.
The plan understood to have been adopted was that of
Mr. Shepherd.
Balloons were inflated and set free, having printed packets of paper or oil-silk, which were distributed occasionally as the balloon traversed across the country.
The papers contained directions, stating the latitude and longitude of the exploring ships, the direction in which they were proceeding, and the localities at which provisions had been left.
These papers were attached at intervals to a long slow-match made of rope, dipped in niter, and the match, burning gradually away, released the notices consecutively, and thus distributed them over a wide expanse of country.
Mr. Darby constructed signals attached by a string to a hollow fuse, which released the
petard signal, whose contact with the ground caused an explosion equal to that of a 6-pounder cannon, and released hundreds of little packets of printed notices wrapped in tin-foil.
The petard called attention to the spot, and the bright little packages would be easily observed, and would be attractive to the natives by whom they might be discovered.
Mr. Darby had also a bill-distributor attached to his to deliver notices.
A third of his devices was a hollow shell containing the information to be disseminated, and a vertical staff with a flag.
The tripod base was so arranged as to stand erect on land or water.
Our informant states that each of
Mr. Darby's plans was tried and worked successfully.
See lists under alarm; electrical appliance; telegraph. See also Si Ren; semaphore; Railway-signal; fire-alarm telegraph.
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Steamboat-signal apparatus. |
