ON SOME MARVELS IN TELEGRAPHY. 235 



at great distances." The letters were represented by various 

 combinations of straight lines, which might be agreed upon 

 previously if secrecy were desired, otherwise the same forms 

 might represent constantly the same letters. With four 

 straight planks any letter of this alphabet could be formed 

 as wanted, and being then run out on a framework (resem- 

 bling a gallows in Hooke's picture), could be seen from a 

 distant station. Two curved beams, combined in various 

 ways, served for arbitrary signals. 



Chappe, in 1793, devised an improvement on this in 

 what was called the T telegraph. An upright post sup- 

 ported a cross-bar (the top of the T), at each end of which 

 were the short dependent beams, making the figure a com- 

 plete Roman capital T. The horizontal bar as first used 

 could be worked by ropes within the telegraph-house, so as 

 to be inclined either to right or left It thus had three 

 positions. Each dependent beam could be worked (also 

 from within the house) so as to turn upwards, horizontally, 

 or downwards (regarding the top bar of the T as horizontal), 

 thus having also three positions. It is easily seen that, 

 since each position of one short beam could be combined 

 with each position of the other, the two together would 

 present three times three arrangements, or nine in all ; and 

 as these nine could be given with the cross-bar in any one 

 of its three positions, there were in all twenty-seven possible 

 positions. M. Chappe used an alphabet of only sixteen 

 letters, so that all messages could readily be communicated 

 by this telegraph. For shorter distances, indeed, and in all 

 later uses of Chappe's telegraph, the short beams could be 

 used in intermediate positions, by which 256 different signals 

 could be formed. Such telegraphs were employed on a 

 line beginning at the Louvre and proceeding by Montmartre 

 to Lisle, by which communications were conveyed from the 

 Committee of Public Welfare to the armies in the Low 

 Countries. Telescopes were used at each station. Barrere 

 stated, in an address to the Convention on August 17, 1794, 

 that the news of the recapture of Lisle had been sent by 



