TEL 



the top of each of which was pivoted a pair of arms. Each 

 pair of arras was capable, by assuming the various posi- 

 tions indicated by the dotted lines added to the first pair, 

 of forming more than a sufficient variety of distinct sig- 

 nals to express any of the numerals or the ; and con- 

 sequently the whole machine could represent any num- 

 ber composed of not more than four figures, besides 

 having several signals to spare. In 1809 Captain Pasley 

 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- 

 firth volume of the periodical just mentioned. This sim- 

 plified polygrammatic telegraph, represented in Fig. 6, 



Fig. 6. 



X 

 N 



lias three pairs of arms, representing hundreds, tens, 

 and unit*, pivoted to different parts of the same ver- 

 tical post. This contrivance is adopted by Lieutcuant- 

 ( 'olonel Macdonald, with very trifling \ariation, in liis 

 ' Treatise explanatory of a new System of Naval, Military, 

 and Political Telegraphic Communication,' published in 

 Inly. By the addition of a ball and vane at the top of 

 the mast, it becomes a machine of the same power as 

 Maedonald's thiiteen-shutter telegraph; as each pair of 

 anus is capable of assuming fifteen distinct positions. An- 

 other semaphore on the same principle was submitted to 

 the Society of Arts in 1821, by Lieutenant N. H. Nicolas, 

 anil dcscnbed. together with a method of applying a 

 shirting key to telegraphic communications, for the pur- 

 pose of insuring their secrecy, in the thirty-ninth volume of 

 the Society's Transactions ;' where, although allusion is 

 made, in a note, to the similar plan published by Colonel 

 Mucdonald, nothing is said of the earlier invention of 

 Pa-Icy. The telegraph of Lieutenant Nicolas consists of 

 a lolly pole with four pairs of arms, one above another, 

 the lowest pair representing units. For each of the three 

 hmei- pairs til' arms nine positions are all that are required, 

 t) licnig indicated by both arms being closed into the post, 

 and therefore concealed from sight ; bat the upper pair 

 are iiiiiiie to represent any number from 1 to 15, so that 

 the total range of the machine is from 1 to 15,999.* This 

 i^ cUcctcd by making the right arm represent 1, 2, or 3, 

 iing to its portion as inclined upwards, extended hori- 

 /iintally, or inclined downwards; and assigning to the letl 

 arm the number 4 if inclined downwards, or H if extended 

 horizontally. 5, (}, 7, and !) art- formed, respectively, by the 

 combination of the signs for 4 and 1, 4 and 2, 1 and 3, and 

 H and 1 : and, in the case of the pair of arms which re- 

 nt, thousands, the left arm when inclined upwards 

 indicates 12: ami lo, 11, l:{, 1 I, and 15 are produced by 

 H ami 2, 8 and :i, 12 and 1, 12 and 2, and 12 and 3, re- 

 ively. The telegraphs upon the commercial line of 

 iinnication recently established between London and 

 the Downs are constructed upon another modification of 

 the polygrammatic principle ; four pairs of arms being em- 

 ployed, but mounted upon two posts instead of one, as in 

 the semaphore last described, or four, as in the original 

 dr-ign of Captain Pasley. 



In IslG it. was determined to change the Admiralty tele- 

 graphs int i M-rnaphores constructed on the principle of 

 i in France, with the improvements suggested 

 by Sir Home Popham, who had previously done much for 

 the improvement of naval signals. The action of Pop- 

 ham's semaphore is explained by Fig. 7, in which dotted 



K.i imuro number stit^'lin the description of tin- m.vhlii' 1 ; 



liMt:l .t for 15,999, u no means is fleacrilf't t<" i>r > 



in' uuwwr !>', tlUiuii^li it u ewy to conceive bow U might be dune, 

 U uewtar/. 



TEL 



lines are added to show the various positions in which the 

 arms may be placed, and numerals to show the numbers 

 indicated by those positions. Only two arms are em- 

 ployed ; but as they are mounted upon separate pivots, 



Fig- 7- 



-: 4 



each of them can assume six different positions, and the 

 two together are capable of affording forty-eight signals ; 

 which number, though less than that given by the six- 

 shutter telegraph, is sufficient to express the letters of the 

 i alphabet and the Arabic numerals, and to leave thirteen 

 signals unappropriated, for abbreviations and arbitrary 

 signs. This kind of semaphore is still used at the govern- 

 ment stations ; and for the following table of its various 

 changes or positions, and of the letters and numbers in- 

 dicated by them, we are indebted to the article ' Tele- 

 graph,' in the seventh edition of the ' Encyclopaedia Bri- 

 tannica,' by Sir John Barrow, one of the secretaries to the 

 Admiralty. 



Tallin of the separate or distinct Signals given by the 

 Admiralty Telegraph, irith their respective Significa- 

 tion*. 



SirHomePopham's telegraph, in addition to its superiority 

 in the important quality of simplicity, was a great improve- 

 ment upon those which preceded it in the details of me- 

 chanical construction and in the mode of effecting the re- 

 quired movements. These are minutely detailed and illus- 

 trated with engravings, in the thirty-fourth volume of the 

 ' Transactions' of the Society of Arts, in whose museum a 

 model of the telegraph is deposited. The vertical post or 

 beam is not a solid mass of timber, but a hollow hexagonal 

 mast, which, turning on a pivot at its foot, and in a collar 

 where it passes through the roof of the cabin used as an 

 observatory, may be moved so as to display its signals in any 

 direction. The moveable arms are provided with balance- 

 weights in the form of masses of metal attached to their 

 shorter ends, very near to the pivots upon which they 

 turn, by which means they are enabled to move in any 

 direction with the exertion of a very small force ; and they 



