394 



ELEMENTARY LESSONS ON [CHAP. xn. 



plates (see Fig. 160) sunk in the ground. Gintl (1853) and 

 Stearns (New York, 1870) devised methods of duplex signalling. 

 Stark (Vienna) and Bosscha (Leyden, 1855) invented diplex 

 signalling, and Edison (Newark, N. J., 1874) invented quad- 

 ruplex telegraphy. jFor fast-speed work Wheatstone devised his 

 automatic transmitter, in which the signs which represent the 

 letters are first punched by machinery on strips of paper ; these 

 are then run at a great speed through the transmitting instru- 

 ment, which telegraphs them off at a much greater rate than if 

 the separate signals were telegraphed by hand. Hughes devised 

 a type-printing telegraph. Wheatstone invented an ABC tele- 

 graph in which signals are spelled by a hand which moves over 

 a dial. For cable-working Sir W. Thomson invented his mirror 

 galvanometer and his delicate siphon-recorder. It is impossible 

 in these Lessons to describe more than one or two of the 

 simpler and more frequent forms of telegraphic instruments. 

 Students desiring further information should consult the excel- 

 lent manuals on Telegraphy by Messrs. Preece and Sivewright, 

 and by Mr. Culley.^ 



424. Single -Needle Instrument. The single- 

 needle instrument (Fig. 158) consists essentially of a 

 vertical galvan- 

 ometer, in which 

 a lightly hung 

 magnetic needle 

 is deflected to 

 right or left 

 when a current 

 is sent, in one 

 direction or the 

 other, around a 

 coil surrounding 

 the needle ; the 

 needle visible in 

 front of the dial 

 is but an index, 



Fig. 158. 



the real magnetic needle being behind. A code of 

 movements agreed upon comprises the whole alphabet 

 in combinations of motions to right or left. In order 



