TELEGRAPH. 



»nd this frame fiipports ten radial bars, which diverge from 

 the common centre of motion. Tlie radii arc again inter- 

 fected by other bars, forming four concentric arcs of 

 circles, each correfponding in radius with the length of one 

 of the four pointers or fignal-boards. By means of the 

 radii, the pofitions of the pointers, and their correfponding 

 numbers, are read off, wliilil the arcs ferve to diftinguifli 

 the different pointers of units, tens, hundreds, and thoufands, 

 becaufe they always (liew the length of the arms from the 

 centre. By this machinery, 10,000 can be exhibited ; and 

 for higher numbers, there are two fquare fignal-boards, 

 which can be turned fo as to be inviCble or vifible at pleafure ; 

 one reprefents 10,000, and the other 20,000, and both toge- 

 ther 30,000, either of which numbers is to be added to the 

 number (liewn'by the arms, according as thefe fignal-boards 

 are exhibited. By this addition, this telegraph can exhibit 

 as high as 40,000. 



The frame with radial bars is a good method of reading 

 off the exact pofition of the arms ; and it is fo much more 

 certain than trufting to the eye alone, that by its aid the 

 arms may be fliewn in a much greater number of pofitions ; 

 ftill, if each arm is diftindly capable of exhibiting ten fignals, 

 it will be fufficient for the numeral method. Mr. Edge- 

 worth's pointers, as we have feen, were only capable of 

 eight pofitions for each ; and this obliged him to mutilate 

 the fyllem of numbers, by taking away all the eights, nines, 

 and zero. 



The dial-plate of a clock has been propofed as a model, 

 and would make a mod excellent telegraph, as it might 

 exhibit 144 figns, fo as to be vifible at a great diftance. 

 The dial fhould only be divided into fix divifions inftead of 

 twelve ; and this being raifed twenty or thirty feet above 

 a building, and the indices and the dial being painted with 

 very diftinft colours, would be clearly vifible. The dial, 

 if fupported on one port, might be always turned to the 

 direftion in which the information was to be conveyed. 



In the Supplement to the Gentleman's Magazine for 1 794, 

 a telegraph is defcribed, which confifl:s of a femi-circle 

 placed in a vertical pofition on a flrong ftand. The circum- 

 ference is divided into tvs'enty-four divifions, which are ren- 

 dered vifible by circular holes cut through the femi-circle. 

 In the centre is an index, which can fucceffively be brought 

 to point out any divifion, very much in the manner of the 

 dial of a clock. In the night-time each divifion is to be 

 furnilhed with a lamp, and the index is made fufiiciently 

 broad to eclipfe or hide any of the lamps at pleafure to 

 which it is turned, and by this means the letters of the 

 alphabet are to be defignated. 



Mr. Garnet's Telegraph Of all the propofals for making 



a variety of fignals by the different pofitions of an index or 

 pointer which moves on a centre, the following is the moll 

 certain as to the identity of the pofitions, and hence it admits 

 of the ereateft number of fignals from each pointer. It has 

 alfo a farther advantage, that tliere is no neceflity for any 

 frame or dials, like the three laft defcribed machines, which, 

 as their divifions are intended to be obferved at, a diftance, 

 muft be exceedingly large. The pointer or indicator of 

 Mr. Garnet's machine is i\\t fame as the foregoing, and its 

 different pofitions reprefent different charafters or letters : 

 its length fhould be two and a half or three feet from the 

 centre, for every mile of diftance. The diftant obferver 

 can find out, and exaftly read off thefe pofitions by a wire 

 fixed acrofs the eye -piece of the telefcope with which he ob- 

 ferves, which eye-piece turns round on the end of the tube of 

 the telefcope, fo as to bring the wire to be parallel to, or cor- 

 refpond with the diftant pointer. This is as eafy to do as 

 to look through the telefcope. 



The index or pointer has a fmall circle fixed on its axis 

 of motion, and turning round with it. This circle is divided 

 into twenty-four divifions, or even more, and each divifion is 

 lettered with a letter of the alphabet. A fixed index is alfo 

 provided, to wliich any letter on the divided circle can be 

 brought by turning the pointer round, and this determines 

 the pofition of the pointer. Or, inftead of an index, the 

 divided rim of the circle may be concealed in a box, with a 

 hole at one fide juft fufficient to fee one letter or divifion at 

 a time, and then there can be no miftake in fetting the 

 pointer. The eye-piece of the telefcope is to be made to 

 turn round upon the end of the tube, and is to have a circle 

 fixed upon it fimilarly divided and lettered. A fine wire 

 is alfo to be ftretched acrofs the centre of the eye -piece in the 

 focus of its lenfes ; and there muft be likewife an index or 

 mark on the telefcope, to read the divifions of the circle on 

 the eye-piece. If this circle be likewife enclofed in a box, 

 having a hole to fee only one letter at a time, there will be 

 lefs danger of miftake. 



The inftrument being correctly adjufted, it is obvious 

 that (the eye-piece of the telefcope being turned round till 

 its wire covers or becomes parallel to the diftant pointer) 

 the index on the telefcope will point out the fame letter on 

 the divided circle of the eye-piece, as is indicated by the 

 index and circle of the diftant pointer : hence the two parties 

 have the fame letter or charafter prefented to them by their 

 refpeftive inftruments. 



The idea of reading the fignals by means of wires on the 

 eye-piece of the telefcope is very valuable, and promifes 

 many advantages. In intermediate ftations, there is always 

 danger of confufion in making fignals to parties in both di- 

 reftions ; becaufe an arm which inchnes towards the right 

 when the telegraph is viewed in one direAion, in an op- 

 pofite direftion vrill appear to incline to the left, and 

 indicate a different thing : hence it is always neceffary for 

 the parties to be informed, by a previous fignal, in what 

 direction the communication is to be made, that the ob- 

 fervers, when they fee a iignal made, may know whether it 

 is intended for them, or for the next ftarion beyond. Now 

 when the telefcope is ufed, if the circle of each telefcope be 

 figured to correfpond with the circle of the pointer which is 

 to be obferved with it, all fignals will become intelligible to 

 any party who obferves them. 



The Rev. John Gamble fuggefted a form of telegraph, 

 which confifted of four arms, each ten feet long, and fur- 

 nifhed with a circular board .it the end. All the four moved 

 upon a common centre of motion, and independently of each 

 otlier, fo that one, two, three, or four, could be exhibited 

 at different degrees of elevation with refpeft to the 

 horizon, or with refpeft to each other, fo as to afford a 

 great number of fignals. One of thefe was erefted in 1 803 

 upon one of the towers of Weftminfter Abbey, but has long 

 been removed. About the time when telegraphs were firft 

 ufed, this gentleman publifhed a fmall pamphlet, entitled 

 " Obfervations and Telegraphic Experiments," which 

 contains fome good ideas. 



Nodurnal Telegraphs. — In 1801, Mr. John Boaz of Glaf- 

 gow obtained a patent for a telegraph, which effefted the 

 fignal by means of twenty-five Argand lamps. Thefe were 

 arranged in five rows, with five in each row, fo as to form a 

 fquare. Each lamp being provided with a blind, with which 

 its light could be obfcured, the lamps could be made to 

 exhibit letters and figures, the fame as Dr. Hooke's charac- 

 ters, by leaving fuch lamps only vifible as were neceffary to 

 form the charafter. The mashine is defcribed in the 

 Repertory of Arts, Firft Series, vol. xvi. p. 223 ; and in the 

 Philofophical Magazine, vol. xii. p. 84. 



