MULTIPLEX TELEPHONY AND TELEGRAPHY—SQUIER. 145 
phone F’ the detector D is operatively connected; E is the earth 
connection. 
The local battery telephone sets are connected across the two line 
wires in the usual manner. In both sets 1 is the microphone trans- 
mitter; 2 is the local battery; 3 is the induction coil; 4 is the ringing 
system, including the bell and hand generator; 5 is the switch hook; 
6 is the telephone receiver. 
Tt was found that cross-talk was heard in the detector circuit from 
the battery transmitter at the transmitting end when the detector 
circuit alone was connected directly to earth from the line without 
any tuning coil or condenser. If, however, the tuning condenser was 
inserted, this cross-talk entirely disappeared, even though the tuning 
coil was not inserted. This is because the impedance of the small 
tuning condenser is large for telephonic frequencies, while the tuning 
coil impedance admits these telephonic frequencies. Both elements 
of tuning are required for selective absorption of energy, so that the 
high-frequency circuit is available as an additional telephonic circuit. 
With this arrange- 
ment talking in the 
transmitter of the 
high-frequency side 
of the system was 
heard only in the 
detector and there 
was no. cross-talk 
from the ordinary 
local battery  cir- 
cuit. Similarly, 
there was no effect of the high-frequency transmission on the local 
battery transmission, and the two telephonic messages were com- 
pletely separated. Both circuits were entirely free from earth dis- 
turbances. 
The volume of speech at the receiving end of the cable is greatly 
increased by simply inserting the transmitter in the dynamo circuit 
and operating this circuit at or near resonance. In addition, the 
coupling at both transmitting and receiving stations should be so 
designed as to permit adjustment for optimum. 
The frequency used in this experiment was about 100,000 cycles 
per second. The talk on the regular battery circuit was of the usual 
high standard both ways, so that the only reason at this point why 
complete duplex-diplex telephony was not obtained was the fact that 
there was no high-frequency dynamo available at the laboratory. 
There is, however, available at this laboratory one of the latest forms 
of the high-frequency arc, and accordingly this was arranged with 
suitable electromagnetic constants to give a period of about 71,000 
38734°—sm 1911——10 
Fig. 4. 
