Description of the French Telegraphs, 341 



constructed upon one post instead of several, is, that in 

 the former the combinations are more hmited in num» 

 her. The signal made at A in fig. 5, for instance, can- 

 not be made" cither at B, C, or D in the same figure, 

 ahhough it may be made on all the posts A, B, Cand D 

 in fig. 6. Hence, wliilst each post in fig. 6 can make 

 twenty-eight distinct signals, that niunber in fig. 5 is li» 

 niited to the part A alone, the signals that may be made 

 at B, C or D, in fig 5, being only twenty-one. 



A polygram matic telegraph upon one post, on the prin- 

 ciple shown in fig 5^ may be thought, however, sufficiently 

 powerful and copious. 



If four pair ot arms are used, the. total number of di- 

 stinct signals that may be made by the parts A, B, C and 

 D con)bined, will he no less than 308,791 



If only three pair of arms are used, in whi:;h case the 

 upper part ot the telegraph niay be supposed cut off at the 

 letter B in fig. 5, the number of distinct signals that may 

 be made by this kind of telegraph (by the various com- 

 binations upon the parts B, C and D) will be 13,935. 



If we suppose all the upper part of the telegraph to be 

 cut off a little above the letter C in fig. 5, so that only 

 two pair of arms are used, the number of distinct signals 

 that may be made by this telegraph (by the combinations 

 upon the parts C and D alone) will be 637. 



Hence, even in this reduced state, ' my polygrammatic 

 telegraph, whether constructed upon one or upon two posts, 

 will preserve a considerable superiority over the French as 

 well as over the British Admiralty telegraphs; and it may 

 perhaps be allowed, that, in all cases, it will be perfectly 

 clear, and as little liable to mistake, as any other telegraph 

 that has been invented. 



A disadvantage attends the polygrammatic telegraph 

 upon four posts, in the form in which it was originally 

 published (fig, 6), arising from the great space upon 

 which the posts must stand ; so that, if the arms are 

 supposed to be six feet long, (measuring from their centre 

 of motion,) the distance AD in that figure can hardly be 

 less than forty feet. This disadvantage will be done away 

 by making the posts of unequal freights, in the manner 

 shown in fig. 7. By this method, the arms being still sup- 

 posed «ix feel long, the distance AD may be reduced to 

 twenty-two feet; so that the telegraph may be conveniently 

 (itted to the roof of the sm.allest building. 



C. W. Pasley, 

 Captain Royal Engmeers, 



Y 3 LVI. On 



