MULTIPLEX TELEPHONY AND TELEGRAPHY—SQUIER. 149 
this range than the higher ones, although meine 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 deine in ake wire 
at about 30 cycles per second and at a polteee 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 arid 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 
Miemscniscu as Snowl clas ep Um pelted 
grammatically in figure 7, ee “ais 
in which Land L’ arethe ~~~ oi 0 oz 
secondary coils of the a U 
transmitter and receiver, 
respectively. C and C’ 
represent variable con- rere 
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. 
TII.—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- 
