TELEGRAPH. 



tina pofitions, as is fticwn by the dotted lines A i, As, 

 A 3, &c. ; but the other two arms, B and C, can only ex- 

 hibit fix pofitions each, becaufe they are hidden by the poft 

 when in a vertical pofition. The total number of combina- 

 tions, or of dillina fipials, which can be made by this tele- 

 graph, will conftaiitly'be three hundred and ninety-one ; but 

 a« the arm A, when in the vertical pofition A 4, may appear 

 to be part of the poft, R, it is not fafe to employ that 

 pofition, and this will reduce the number of fignals to three 

 hundred and forty-two. As only three bodies are employed 

 in this telegraph, it appears very fuperior to the Ad- 

 miralty telegiaphs ufed in England, which, by the combina- 

 tion of double that number of bodies, can only make fixty- 

 three diftind fignals. Captain Pailey obferves, that the 

 mechanifm of the French telegraphs jull defcribcd, muft 

 be either imperfeft, or the men employed in working them 

 muft have been very unlkilful, for the fignals were made and 

 repeated in an awkward manner, with what feemed to him 

 much unneceffary lofs of time. But thefe defefts, it will 

 be evident, detrad nothing from its merit as an invention. 

 In regard to the mechanical conftruftion, he could only ob- 

 ferve that the arms, which were painted black, and appeared 

 folid at a diftanee, were made in the fafliion of a Venetian 

 blind, in order, it may be prefumed, to diminifh the aftion 

 of the wind in bad weather. Each arm had a counterpoife 

 of thin materials painted white, which, unlefs the obferver 

 be very near the telegraph, becomes invillble. 



Fig. 5. fhcws the telegraph in a Hate of reft, the dotted 

 Knes marking the feveral pofitions in which the arms can 

 be exhibited. Fig. 6. is a fpecimen of the telegraph 

 at work. Fig. 7. (hews the conltruftion of one of the arms 

 on a larger fcale, D E being the part which is fafliioned 

 like a Venetian blind, and E F the counterpoife. 



Sir Home Popham's Telegraph at the yidmiralty. — The 

 original telegraphs at the Adrniralty, with the fix boards, 

 have been lately taken down, and a new kind fubilituted. 

 It is on the fame principle with the French, being an upright 

 maft with two indicators, which move upon centres one 

 above the other, in the manner of the laft defcribed. The 

 maft is made to turn round on its vertical axis, fo as to pre- 

 fent its arms fucceffively to all quarters, when required. 

 The mechanifm, which is the invention of fir Home Pop- 

 ham, is the bcft which has ever been contrived, the move- 

 ments being very fimple, and efi^efted by iron fpindles and 

 endlefs Icrews, fo that the indices below are certain to ac- 

 company the indicators exaftly in their movements, and 

 place them precifely in their required pofitions, which cannot 

 be done by the old machinery with cords, becaufe they are 

 liable to expand and contraft by wet or dry weather. The 

 machinery for this fet of telegraphs was conftrufted in the 

 moft fubftantial manner by Mr. Maudflay in 1 8 16. (See 

 ^^j. 8, 9, and 10. ) L M is a tall maft of an hexagonal form, 

 framed up from fix fir planks put together at the angles, 

 and bound by iron hoops at different places, fo as to be 

 hollow within. The lower end, L, terminates in a pivot, 

 and the maft is retained in a vertical pofition by a circular 

 collar at O, which embraces it, and is fupported in the roof 

 of the building. The two arms, P M and Q R, are move- 

 able upon centres, one at the top of the maft and the other 

 half way down. When the arms are placed in a vertical 

 pofition, they fhut up within the hollow of the maft, fo as 

 to be entirely concealed ; and for this purpofe, two of the 

 fix fides are cut away at the upper part, fo as to leave an 

 opening through the maft of fufiicient width to admit the 

 two arms to work in it. To communicate motion to the 

 arms, a fmall toothed wheel is fixed upon each arm at the 

 centre of motion, and clofe to the fide of the arm. The 

 10 



teeth of thefe wheels aie aftuated by endlefs fcrews or 

 worms, formed on the upper ends of the long fpindl'\s d eanA 

 fg, which defcend down to the bottom of the hollow maft, 

 and have fmall bevelled wheels upon them, which are aftuated 

 by wheels of fimilar fize, fixed on the ends of ftiort horizontal 

 fpindles, which have handles, p, q, applied at the extremities. 

 ( See Jig. II.) By turning thefe handles, motion is given 

 to the vertical fpindles d andy"; and by means of the endlefs 

 fcrews upon the upper ends of them, the wheels at M and R, 

 on the centres of the arms, are turned round, and the arms 

 are put into any required pofition. But in order that the 

 people below may at all times know exactly what pofitions 

 the arms ftand in, two dials, m and r, are formed on the 

 lower part of the maft, the upper one, m, being for the upper 

 arm M, and the other, /-, for the lower arm R ; and each dial 

 has an index or Iiand, which turns round with a motion ex- 

 aftly correfpoiiding to the motion of the arms. For pro- 

 ducing this motion, the axle of each hand or index has a fmall 

 toothed wheel, ,f or /, (Jig. 1 1 .) fixed upon it in the middle ; and 

 an endlefs fcrew is formed upon the upright fpindle to work 

 in the teeth of the wheel. The wheels upon the centre of 

 the arms, and thofe upon the axes of the indices, have the 

 fame number of teeth ; and as every turn of the fpindles and 

 fcrews will move the wheels round one tooth, the angular 

 motion of the arms, P M and Q R, and the hands, m and r, 

 will in all caies be the fame. 



The dials are each divided into eight, correfponding with 

 the eight pofitions in which the arms are to be exhibited : 

 viz. pointing vertically ; ift, upwards ; and 2d, downwards : 

 pointing horizontally ; 3d, to the right ; and 4th, to tlie 

 left : pointing upwards at an inclination of 45 degrees ; 

 5th, to the right ; and 6th, to the left : pointing downwards 

 at an inclination of 45 degrees ; 7th, to the right ; and 

 8th, to the left. But of thefe eight pofitions, only the four 

 laft are made ufe of to reprefent characters ; becaufe, in the 

 two vertical pofitions, the pointers enter within the maft, 

 and cannot therefore be feen whether they are pointing up- 

 wards or downwards : the horizontal pofitions of the arms 

 are referved for -the neceflary fignals of preparation, &c. 

 Each arm, then, has four pofitions, in which it will exprefs 

 different fignals ; and thefe pofitions are all made with the 

 pointer, at an inclination of 45 degrees from the horizontal 

 line. 



Thefe fignals either exprefs the letters of the alphabet, 

 or the numeral charafters, according to previous arrange- 

 ment, which muft be made known by exhibiting a prepara- 

 tory fignal, before the commimication is begun. The fignal 

 to prepare for receiving letters is the lower arm extended 

 horizontally to the right ; and for the nimierals, both armt 

 are extended horizontally to the left. 



The upper pointer, P M, ufed by itfelf, at an elevation of 

 45 degrees, denotes, 



A, or I, when pointing upwards to the left. 



B, or 2, when pointing downwards to the left. 



C, or 3, when pointing upwards to the right. 



D, or 4, when pointing downwards to the right. 



The lower pointer, Q R, ufed by itfelf, at an elevation of 

 45 degrees, denotes, 



E, or 5, when pointing upwards to the left. 



F, or 6, when pointing downwards to the left. 



G, or 7, when pointing upwards to the right. 

 H, or 8, when pointing downwards to the right. 



It is eafy to conceivej that, by repeating all thefe pofi- 

 tions with both arms exhibited together, inftead of one 

 fingly, various com.biuations inay be made, which are fuf- 



ficient 



