ifliiiiii!iii!'sii'^yiii?€ 



" 'lib ■■ 



Figure 44. — Above, and onjaang page: English telegraph offices of the mid-igth century. 

 From T. Shaffner, The Telegraph Manual, New York, 1859, pp. 233, 235. 



identical commutator moving synchronously at the re- 

 ceiving station switched the combinations of signals to 

 four groups of polarized relays, each relay being con- 

 nected to one of the five subdivisions of the four seg- 

 ments of the receiving commutator. Each group of 

 relays actuated a certain one of the four printers at the 

 end of the line. With this device the operator at each 

 transmitting station could send about 150 letters per 

 minute. (See figs. 49-53.) 



Also tried was another method of multiple teleg- 

 raphy that used different transmitters — each with its 



own characteristic frequency of alternating current — 

 that sent the different currents simultaneously 

 over the common line. These currents were sepa- 

 rated at the receiving end of the telegraph by use 

 of analyzers, each of which was sensitive to only 

 one frequency. This method of communication did 

 not have any commercial success until the 20th 

 century, but such harmonic multiple telegraphy led 

 to another means of electrical communication. After 

 trying to send tones and combinations of tones over a 

 telegraph line, some inventors went on to study the 



310 



BULLETIN 228: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



