SIGNALS are the means of transmitting intelligence to a greater or less distance by the agency of sight or hearing. Incomparably the most powerful medium yet known for this purpose is the electric current. See TELEGRAPH. Sound signals have obviously but a short circuit. The electric current requires fixed apparatus establishing an actual communication betwkn the two points; and is therefore inapplicable to the ordinary cases of ships interchanging signals with each other or with the shore; and, except under unusual circumstances, it would not apply'to armies maneuvering in the field. For these purposes, so far as present knowledge extends, signals by sight or sound must always be the resort. For railway signals, see RAILWAYS.
The ancients seem to have elaborated a fair system of night-signals by torches fob military purposes; but in naval affairs the ships sailed so close together that orders could be communicated by word of mouth, while the turning of a shield from right to left sufficed as sailing directions to the several lines. In modern times signaling between ships has become indispensable; but there is probably no department of practical science in which progress has been slower, and every so-called system of signals has been dis tinctly without any system whatever. In the time of James II. a signal could only be expressed by flags, in confusing number, hung in different parts of the vessel. By the commencement of the present century. thanks to sir Home Popham and other inventors, the system had been adopted of hanging a number of flags under one another, each symbol or combination having an arbitrary conventional meaning attached to it. Altera tions iu the specific flags have been made from time to time, but essentially this is the system now in use. The flags are either square, triangular of the same length, or pep dants which are pointed and longer. These arc of black, white, red, blue, and yellow (in the Austrian service alone green is added) in mass or in combination. Specimens of the flags in use in the present naval code are shown in Fig. 1. The signalmen'find, how ever, that at a distance blue, red, and black are not readily distinguishable, nor yellow from white. It has consequently been the recent tendency, and apparently mpst justly, to reduce all the signs to black and white, singly or in combina tion, trusting to shape for different signals.
There are, however, disadvantages attending flags. In a still day they are difficult to read; or the wind may so blow that they are only seen end on.
At sea the motion of a ship will gen erally neutralize these drawbacks; but the case is otherwise on shore, and it may consequently occur that the ship can com municate to the land, but cannot get a reply. To obviate this signals representing solid figures are sometimes employed. To fulfill their conditions they must appear the same in whatever lateral direction seen. But this limits the shapes to cylinders, cones, and the sphere, or combinations of those figures; and as the total number of distinguish able sig,ns is reduced, signaling becOmes reduced from the word-signal to the telegraph.
This distinctionshould be clearly understood, as much is involved in it. A word signal, as in the present system, is where the whole word or message is sent up at once, and flies simultaneously; a telegraph signal is one in which the letters composing the word or numbers representing the signal are shown separately, and each is removed before another is shown. At sea the word-system is best, for itiinvolves no act of memory; and memory, even from signal to signal, is found difficult by signalmen in the turmoil of perhaps storm or fighting. On the other hand, the telegraph system involves far simpler apparatus, and the changes can be effected more rapidly. As regards the actual time required for a message, the' word-system has the advantage in a message short enough for the whole to be shown at one time; but otherwise the difference is not material. If all advantages be balanced, it is probable that the telegraph system will eventually supersede the other entirely. Whether the word or the telegraphs system be practiced, another question is, whether to spell each word, or to use numerals and a code. Under the latter principle about 14,000 of the words and sentences most com monly sent are arranged for easy reference in the signal-book. With the addition of 1 or 2 repeating symbols the 9 numerals and 0 give combinations 4 together to this number. A combination of figures is arbitrarily assigned to each expression,; and the expression is communicated by representing those figures in their proper order. With the book of reference at'haud, and intelligent signalmen, there can be no doubt of the superior rapidity of the "code." A code has also this further advantage, that, the sig nals representing things and not words, it can be made international, the same symbols representing the same idea in every language. It is then only necessary for universal signaling that each nation should concur in the meaning to be attached to the several signs. iliany gentlemen of ability have devoted their attention of late years to the sim plification of signals; among whom conspicuous positions must be assigned to col. Grant, col. Bolton, Mr. Redr, and rapt. Colomb. RN. Their principal object has been so to simplify the telegraph system that signals may be made with any apparatus, or without apparatus at all. To accomplish this they have, to a great extent, abjured color and resorted to form and motion. Among the form telegraphs there is the princi ple of the old semaphore (q.v.), in which each letter or number• is shown by the position of two arms, as in Fig. 2. The arms are heavy, and involve mechanism: besides which they are not always clear on a ship in motion beyond a short distance.