HISTORY AND PROGRESS. 23 



first to have occurred to Ampere, who explains it in 

 a paper read before the Academy of Sciences at Paris, in 

 October, 1820.* 



He says that by means of the same number of magnetic 

 needles and line wires as there are letters of the alphabet, 

 and with the help of a voltaic battery whose poles could be 

 brought in connection, one after the other, with the ends 

 of the wires, a telegraph might be produced by which 

 all possible communications might be made to a person at 

 a distance off, who was charged to observe the needles. If a 

 keyboard whose keys were each marked with a letter of the 

 alphabet were adapted to the battery, so that on pressing 

 down the key of any letter the circuit corresponding to that 

 letter would be closed, correspondence could be carried on 

 with ease, and would only require the time necessary to press 

 down the keys at the one station, and to read off the letters 

 from the deflected needles at the other. 



This telegraph, as imagined by Ampere, was, however, 

 doomed to the same fate as that of Sommering, of never 

 coming into practice, and for the same reasons, principally the 

 number of line wires. Had Ampere combined his system 

 with that which Schweiger proposed of reducing Sommering's 

 telegraph to two wires, or with any other using a code of 

 signals, the problem of the electric telegraph would have 

 been solved from the year 1820. 



But two serious inconveniences the irregularity of the 

 piles, and, above all, the rapid decrease of their intensity 

 only permitted the application of this great idea on a small 

 scale. 



30. Ritchie, however, carried out a really excellent modi- 

 fication of Ampere's invention by encircling thirty magnetic 

 needles with coils of wire ; each needle was furnished with 

 a small screen, so that when it was unaffected by a current, 

 the screen covered over a letter of the alphabet, which was 

 exposed as soon as the needle was deflected. 



This telegraph was first exhibited in public, some years 

 later than the date of its invention, by Mr. Alexander, of 

 * " Annales de Physique et de Chemie," vol. xv., p. 72. 



