TELEGRAPH from 'm x'at a distance, and netlew to write, is the name given to a piece of mechanism for the rapid communication of intelligence by sig nals.
When we find that some of,,the most savage na tions of modern times are acquainted with the use of signals, it would be absurd to suppose that the civilized nations of antiquity had not devised and put in practice regular methods of communicating intelligence both by fires during the night, and by 'movable objects during the day. The Prophet Jeremiah vi. 1. directs the children of Benjamin "to set up a sign of fire at Beth-haccerem, as evil appeared out of the north and great destruction ;" and Eschylus, who lived about two centuries later, makes one of the soldiers in his .dgantenznon descend from a watch tower at the top of the palace and announce from the fire signals the fall of Troy long before the return of the Greeks.
Polybius gives a full account of the TUC" or fire signals of the ancients, and describes his own im provements on the method of telegraphic commu nication invented by Cleoxenus. Kircher in his ".firs magna," Sec. distinctly describes a tele graphic experiment, and Schottus in his Technica curiosa proposes the application of the telescope to view posts erected upon an eminence. The Marquis of Worcester in Nos. 6 and 7 of his Century of In.
ventions enumerates a day and night tetcgrapn among his contrivances : and Kessler in his Con cealed .firts proposes to cut out characters in the bottom of a cask having a light placed within it, the characters being changed in succession in order to express single words, and whole sentences.
The earliest telegraph for general purposes ap pears to be that of our celebrated countryman Dr. Hooke, who has described it in the Philosophical Transactions for 1694. This contrivance consisted of more than thirty different bodies, each of which formed a distinct telegraphic sign or symbol, which were exhibited in succession upon an elevated ap paratus. This apparatus, shown in Plate DXXI, Fig. 1. consists of three long masts or poles, two of which carry a screen A, behind which the thirty bodies hang upon rods or lines. These bodies, con sisting of squares, centres, triangles, and made of deal, may, by the help of small lines connected with them, be exhibited at B, where a square is shown. In the night time torches, or other lights, were ar ranged in a particular order, and were substituted in place of the wooden figures. The characters, which thus represent the alphabet, may be varied, as Dr. Hooke observes, in ten thousand ways, whilst none but the two extreme correspondents shall dis cover the information conveyed.
Long after the publication of Hooke's contri vance, M. Amontons, an ingenious natural philo sopher and member of the Academy of Sciences, brought forward, and submitted to trial, a plan of a telegraph which seems to differ in no respects from that of Dr. Hooke. He proposed to place the stations at such a distance that a telescope could command them. The signals to be seen through the telescope were either to be large letters of the alphabet, or figures to represent them, and he ap pears to have tried the plan before several persons of distinction in the court of France.
In the year 1767 R. L. Edgeworth, Esq. made trial of a new method of carrying intelligence. He made use of a common windmill for the purpose, and he arranged a system of signals produced from the different positions of the arms carrying the sails, the canvass being removed from one or more sails as the circumstances might require. In 1784 the same ingenious author brought forward his plan of a numerical telegraph, the signals denoting num bers, and each party having vocabularies in which all the words were indicated by the number which the signals represented.
Notwithstanding these various attempts to con trive and construct telegraphs, yet the practicability of these machines does not seem to have been dis tinctly recognised till the year 1794, when the ac tivity of the National Convention called into play all the talents of the kingdom. M. Chappe had the merit of introducing, on this occasion, under the name of the Semaphore,t what has been called in England the T telegraph, from its resemblance to that letter. It is represented in Fig. 2, where CD is a strong wooden mast carrying a beam AB, called the long indicator, which can be placed in any position round C as a centre of motion, by means of cords and pulleys. This indicator, which is about twelve feet long, and nine inches broad, carries at each extremity two lesser indicators AE, BF, which are likewise movable round A and B as centres, so that they can be placed in any position with respect to the long indicator AB. Each of the lesser indicators can obviously take five distinct positions with respect to the great one considered as fixed, viz. two at right angles to AC, two in clined 45° to AC, and one where it falls back upon AC and appears, so that we have thus 5 X 5 = 25 signals. But as AD may distinctly take four posi tions, one horizontal, one vertical, and one inclined 45° to the horizon, we have 4 X 25 = 100, for the number of distinct signals given by the semaphore.