In the semaphore constructed at Paris the first station was on the Louvre. The distance of the stations was three or four leagues, and an observa tory was erected near the committee of public safety, to observe the indications on the Louvre. Although the semaphore of M. Chappe possesses great power, yet it is said to have been liable to mistakes, unless when wrought by experienced ope rators.
In t794, Mr. R. L. Edgeworth proposed the tele graph shown in Fig. 3, which consists of four se parate pointers, having the form of an isosceles triangle, with their base rather less than half the perpendicular, and movable round centres at the top of the vertical posts A, B, C, D. The four pointers are placed in a row, and the right hand one D represents units, the next C tens, the third B hundreds, and the fourth A thousands. Now each pointer can take eight distinct positions ; seven of these denote figures, and the upright position of the pointer represents o, or zero. With the figures, as thus indicated by the telegraphs, are contained a vocabulary, with numbers opposite the words.
The Rev. Mr. Gamble produced, in 1795, plans of two telegraphs which are represented in Figs. 4 and 5. The first of them consists of five boards, one above the other, which, by opening and shut ing, afforded a certain number of distinct signals. His second plan consisted of five beams of wood, each ten feet long. All the five moved round a common centre of motion, and as those motions were independent of each other, one, two, three, or four, could be exhibited at different degrees of ele vation, in reference to a horizontal line, or with re spect to each other, so as to furnish a great number of signals. One of these was erected in 1803, on one of the towers of Westminster Abbey, but has been long ago taken down.
In 1808 Major C. Le Hardy described a telegraph consisting of four pointers, or long arms, each car rying at its extremity a square wooden board. One of these represents units; another tens, another hun dreds, and the fourth thousands. The indices move on a common centre, and each index board is placed at a different distance from the centre of motion, so that in turning round, these boards describe four circles of different radii. The inclination of the
arm to the horizon indicates the number, and each has ten different positions. In order to identify these positions, a large frame, with ten radical bars, is fixed behind the pointers, and these are crossed by five circles, corresponding to the bulk of each index board.
Among other contrivances, similar to this in principle, may be numbered that of Dr. Garnet, who proposed to read oft' the inclination of the pointers to the horizon by a wire in the focus of a telescope, which, by turning the end of the tube brings the wire in a line with the pointer, (see Fig. 6,) and indicates its inclination upon a scale.
In 1795, Lord George Murray laid before the Admiralty his plan of a six shutter telegraph, which is shown in Fig. 6. This plan was in use during the whole of the late war, but in 1816 was replaced by a simplified semaphore.
The first French semaphoric telegraph which is said to have been erected on the palace of the Thuil lcries in 1796, is shown in Fig. 8.
In the year 1796, Mr. Edgeworth proposed to simplify this telegraph, by using only one of the masts and one of the isosceles triangles, shown in Fig. 3, and at the same time proposed a two-armed telegraph, one of the arms having the form of a cross, and the other, that of a wood-cutter's sign, as shown in Fig. 9.
In the year 1798, MM. Breguet and Betancourt presented to the National Institute a new telegraph on a simple construction. It consisted only of a single piece, called the arrow, and one of whose extremities was terminated in a T, in order to dis tinguish it from the other end.
At the beginning of the war in 1803, there were erected a series of telegraphs along the coast upon the same principle as the radiated telegraph of Mr. Gamble. Each telegraph consists of an up right post,, as shown in Fig. 10, carrying three arms exactly similar to each other, and each mov ing round an axis of its own. The distance between the centre of motion of two contiguous arms is a little less than double the length of one arm. The uppermost arm exhibits seven distinct positions, and the others have only six each.