./"..... 



RAUNSCHWEIG 



•wOLFEHBUTTtL 



GEHTHIN 



* riAue 



HALBERSIADI 



^BRANDENBURG 



MAGDEBURG 



COBLENZ 



Figure 4. — Map of the German semaphore telegraph system 

 between Beriin and Coblenz during the 1830's. Adapted from 

 Archivjuer Post unci Telegraphle, 1888, vol. 16, p. 230. 



recognize the theoretical basis for such a transmission; 

 that is, that the current in a simple closed circuit has 

 the same value at every point in the circuit. Ampere 

 originally believed that each conductor in a circuit — 

 each of the loops of wire in a coil, for example — 

 required its own chemical cell. Pierre Simon Laplace 

 pointed out to Ampere that the Oersted effect could 

 be produced everywhere in a long conductor, which 

 fact argued for the hypothesis that the galvanic 

 current was everywhere the same. Accordingly, a 

 magnetic needle would be able to indicate the pres- 

 ence of a current when a battery was connected to a 

 wire through which the current was passed, no matter 

 how long the wire or how far away the needle. By 

 using a pair of wires and a magnetic needle for each 

 letter of the alphabet, Ampere suggested that one 

 could communicate at a distance by opening and clos- 

 ing the circuit proper to each letter, for the motion of 

 the needle would indicate the appropriate symbol. 



William Alexander ' demonstrated at an exhibit in 

 Edinburgh in 1837 how such an Amperian needle 

 telegraph might be set up (fig. 8). The distance 

 covered by this exhibit was only 5 feet, but the ex- 

 hibit showed how 30 wires and a copper rod, which 

 was used for the common return, could indicate all 

 the letters of the alphabet and some of the punctua- 

 tion marks. When the battery was connected to a 

 certain wire, the closing of the circuit caused the mag- 

 netic needle associated with that wire to move and to 

 uncover the corresponding letter of the alphabet on a 

 panel. The combinations obtained by closing the 

 circuits in proper order resulted in the transmissions 

 of combinations of the letters that formed a word. 



It would appear that Ampere's suggestion of an 

 electromagnetic telegraph should have led directly 

 to its invention, but, instead, only the first step toward 



' "Alexander's Electric Telegraph," Mechanics^ Magazine, 

 London, November 25, 1837, vol. 28, pp. 122-123; J.J. Fahie, 

 A History of Electric Telegraphy to the Tear 1837, London, 1884, 

 pp. 448-468. 



5\ 



Figure 5. — The semaphore 

 telegraph as adapted to the 

 German railway system by 

 G. A. Treutler. From H. 

 Schellen, Der elektromag- 

 netische Telegraph, Braim- 

 schweig, 1854, p. 15. 



278 



BULLETIN 228: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



