Chappe's telegraph, which, from its position when at rest, is some times called the x telegraph, consisted of an upright pole or post. at the top of which was pivoted, by its centre, a transverse beam, which, by means of ropes worked in the chamber below, that served also for an observatory, might be made to assume any required angle with the post. Each end of this moveable beam carried a short arm, that was capable of assuming any required angle with it ; and these arms also were worked by ropes, which were conducted through the axis of the beam, in order that the necessary degree of tension might not be dis turbed by the action of the machine. By this contrivance, without the use of any angles of less than 45° (which might be indistinct when viewed from a great distance, or under the influence of a refractive atmosphere), as many as 256 different signs might be made. A much smaller number was however sufficient, as M. Chappe communicated his intelligence latter by letter, and simplified the movements by using an alphabet of only sixteen letters. The small figures in the cut show some of the different positions assumed by the beam and arms ; and, as the connection between these and the lettere they were made to represent, was quite arbitrary, their signification might be changed as often as was necessary for the purposes of secrecy ; it being only neces sary that the key should be known to the parties sending and receiving the message, although it might be transmitted through a great number of intermediate stations. Such telegraphs were first erected on a line commencing at the Louvre, in Paris, and proceeding by Montmartre and other elevated points to Lisle, in order to communicate between the Committee of Public Welfare and the combined armies in the Low Countries. Telescopes were used at each station, and the signals dis played at one station were immediately repeated at the next ; four seconds being found sufficient for effecting the required motions, and sixteen seconds the time allowed for observing and noting down each signal, during which the machine remained stationary. Barri:re, in announcing the invention of the telegraph to the Convention, on the 17th of August, 1794, stated that the news of the recapture of Lisle had, by means of this machine, reached Paris in an hour .after the troops of the Republic had entered the place. (` Annual Register,' 1794.) The advantages of such extraordinary celerity of communication were so obvious, that in England and other countries many plans were immediately brought forward, some of which differed materially from that which had been successfully put in practice in France. Among these was that contrived by Mr. R. L. Edgeworth. whose numerical telegraph (or a telegraph expressing numbers, which numbers refer to letters, words, or sentences, in a dictionary), will be understood by Fig. 3.
means of fig. 3, in which an index or pointer, in the form of an hum. celes triangle, was so mounted upon a post, or on a portable triangular stand, that it might be turned into any of the eight positions shown in the upper part of the cut ; these positions indicating, respectively, 0 and the numerals 1 to 7. Four such pointers, mounted side by side, as in the lower part of the figure, afford power for expressing any number from I to 7777, excepting 8, 9, 18, 19, 28, 29, and all others in which the numerals 8 and 0 are required : the first pointer repre senting thousands, the second hundreds, the third tens, and the fourth units. Thus, the four black pointers in the figure being, respectively, in the positions indicating 2, 7, 7, and 4, express, collectively, the number 2774. Further particulars of this method will be found in Edgeworth's ' Essay on the Art of Conveying Secret and Swift Intelli gence,' published in the sixth volume of the Transactions of the Royal Irish Academy.' He also published a pamphlet entitled ' A Letter to the Right Honourable the Earl of Charlemont on the Tellograph, and on the Defence of Ireland,' which was reprinted at London in 1797.
The Rev. J. Gamble, chaplain to the Duke of York, proposed a shutter telegraph, consisting of a frame-work containing five boards, or shutters, arranged vertically one above the other, and pivoted in such a way that any or all of them might be clbsed, so as to present their broad surfaces to the eye, or opened, so as to show merely a thin edge, which would be invisible at a distance. The various signals produced by closing one or more of these shutters may be applied either to a numerical or an alphabetical system. A similar plan sub mitted to the Admiralty in 1795, by Lord George Murray, was adopted in the first government line of telegraphs established in England, in 1796, between London and Dover. The ' Annual Register' for that year (p. 4 of the ' Chronicle ') mentions the erection of the telegraph over the Admiralty on the 28th of January, and states that information had been conveyed from Dover to London in seven minutes. The action of this kind of telegraph, which was continued in use by the Admiralty until the year 1816, is illustrated by fig. 4, in which represents a square frame-work with six octagonal shntters,l, 2, 3, 4,5, and 6, arranged in two vertical columns, or sets, and turned into a vertical position, so as to display their broad surfaces completely, and n represents the same apparatus with the boards or shutters placed horizontally, or turned one-quarter round upon their respective axes, so as to present nothing but their edges to the eye. The central space
between the two columns of shutters serves to render them more distinct to a distant observer, and affords room for the ropes and pulleys by which the telegraph is worked, and which are managed by persons in the observatory below. A modification of this kind of telegraph, intended for night as well as for day service, was submitted to the Society of Arts, in 1805, by Mr. Joseph Davis. About the same time that shutter-telegraphs were being intrediteed in England, the Chevalier A.' N. Edelcrantz, of Stockholm, was devising similar machinery for use in Sweden. (Seo Nicholson's 'Journal; 1803; Society of Arts ' Transactions' for 1808.) Other modifications of the shutter telegraph were put forward from time to time, but experience established the superiority of telegraphs or semaphores with moveable arms ; and these were greatly simplified, so as to avoid the objection raised to the old French telegraph. Among the schemes proposed soon after the first practical application of telegraphs, was one which consisted in dividing a large circle into twenty four parts, for the letters of the alphabet, and employing a traversing radius, or index, to point them out ; wires being fixed before the object-glass of the telescope to enable the distant observer to determine the position of the radius. This plan could only be applied to short distances, because refraction might render it difficult to distinguish between positions so little varying from each other. The same radiating principle was, however, adopted in some machines of a more practical character ; among which was a telegraph contrived by the Rev. J. Gamble, consisting of five beams or arms pivoted at the top of a post, upon one axis, and capable of pro ducing many different combinations without using angles of less than 45°. On a similar principle were constructed the French coast telegraphs adopted in 1803, to which the name of semaphore was first applied, and from which it has been given to other telegraphic machines. the action of which is dependent upon the motion of arms around pivots placed at or near their extremities. These French semaphores, or, as they were sometimes called, s;gnal-posts, consisted of upright posts with two or three moveable arms, turning upon separate pivots, one above the other. Before they were much known in this country, Captain Pesky had been led to observe the inferiority of the common land•telegraph to that used at sea, which consisted of coloured flags, and by which three numbers, or rather three numerals combined to form one number, might be readily expressed. To remedy this defect, he, In 1807 (before he had seen the French semaphore), devised what ha termed a " polygrammatio telegraph," a inscription of which was publiabed in Philosophical Magazine; vol. XXiX. This machine, fig. 5, consisted of four posts, at the top of each of which was pivoted a pair of arms. Each pair of arms was capable, by assuming the various positions indicated by the dotted lines added to the first pair, of forming more than a sufficient variety of distinct signals to express any of the numerals or the 0; and consequently the whole machine could represent any number composed of not more than four figures, besides basing several signals to spare. In 1809 Captain Paaley saw the French semaphore, which he described in the following year, together with a modification of his own polygrammatic telegraph, founded upon it, in the thirty-fifth volume of the periodical just mentioned. This simplified polygrammatie telegraph, represented in fig. 6, has three pairs of arms, representing hundreds, tens, and units, pivoted to different parts of the same vertical post. This contrivance is adopted by Lieu tenant-Colonel Macdonald, with very trifling variation, in his 'Treatise explanatory of a new System of Naval, Military, and Political Tele graphic Communication,' published in 1817. By the addition of a ball and a vane at the top of the mast, it becomes a machine of the same power as Macdonald's thirteen-shutter telegraph ; as each pair of arms is capable of assuming fifteen distinct positions. Another semaphore on the same principle was submitted to the Society of Arts in 1821, by Lieutenant N. H. Nicolas, and described, together with a method of applying a shifting key to telegraphic com munications, for the purpose of insuring their secrecy, in the thirty-ninth volume of the Society's ' Transactions.' The telegraphs upon the commercial line of communication esta blished between London and the Downs were constructed upon another modification of the polygrammatic principle ; four Fairs of arms being employed, but mounted upon two posts instead of one, as in Nicola-it semaphore, or four, u in the original design of Captain Pasley.