MULTIPLEX TELEPHONY AND TELEGRAPHY SQUIER. 149 



this range than the higher ones, although efficient results were easily 

 obtained at any point. 



The battery telephone side of the equipment was left absolutely 

 intact, as it would be commercially used, and severe tests were made, 

 employing four operators, to determine the efficiency of two simulta- 

 neous conversations over this same pair of wires. 



The ringing circuit was operative both ways with no apparent effect 

 on the high frequency telephone transmission. This ringing circuit 

 develops a comparatively large alternating current flowing in the wire 

 at about 30 cycles per second and at a voltage of many times that of 

 either the high frequency or the battery side of the circuit. 



Articulation tests, including music, numerals and other difficult 

 combinations, gave satisfactory results, with no interference what- 

 ever between the two sides of the circuit. 



By holding one telephone receiver to one ear and the other receiver 

 to the other ear the receiving operator could hear two entirely 

 different conversations simultaneously over the same pair of wires. 



(b) series arrangement. 



A circuit was next made up with high-frequency apparatus inserted 

 directly in the line in series, instead of in the bridging arrangement 

 shown in figure 5. The 



circuit used is shown dia- I I 



grammatically in figure 7, yf c ' 



in which L and 1/ are the 55SP 8ffip 



secondary coils of the jf^~\ i J ^S-n 



transmitter and receiver, ^T T §1 "tLi? 



respectively. C and C *-*©^ ' ' 



represent variable con- FlG - 7 - 



densers of the order of magnitude used in wireless telegraphy and serve 

 as low impedance paths for the high-frequency oscillations, and at the 

 same time prevent the short circuiting of the low-frequency battery 

 telephone current. It was found that this arrangement gave appar- 

 ently as good results as the bridging arrangement of the circuit. 



III.— DUPLEX-DIPLEX TELEGRAPHY. 



Having described in detail the experiments for obtaining the 

 simultaneous transmission of two telephonic messages over a single 

 circuit, it will be apparent that the problem of transmitting two 

 telegraphic messages over the same circuit may be solved by methods 

 and apparatus as far as the high-frequency side of the circuit is con- 

 cerned, which are practically identical with those described above. 



In this connection the metallic circuit referred to was equipped 

 with a standard Morse set for manual operation, and upon this cir- 



