MULTIPLEX TELEPHONY AND TELEGRAPHY—SQUIER, 143 
primary circuit of the transmitter were varied individually and rela- 
tively in a variety of ways, with the striking result that just at the 
point where the direct-current voltage was decreased, so that no 
sounds were received, the line became absolutely silent, although the 
alternating voltage in the circuit was at its largest value, or, again, 
speech would reappear at the receiving station at the moment when 
sufficient direct-current voltage was introduced to produce it, and the 
simultaneous presence of both the maximum direct voltage and 
maximum high-frequency voltage in a cireuit produced exactly the 
same result as the 
maximum direct-cur- {7 AANA | 
rent voltage did alone. el ERED tex 
When, however, the | FeuTen are 
high-frequency cur- 
rentin the local circuit 
was forced to a point 
which caused ‘ burn- 
ing”’ in the transmit- 
ter itself, then, and 
then only, did the 
high-frequency cur- ah a 
rent in any way inter- 
fere with the trans- Pore gee 
mission. ae ij i (op 
waitin 
By transferring this 
coil from the local 
circuit of the tele- 
phone set directly into 
the line itself, so that 
the high-frequency 
oscillations would be superimposed upon the line beyond the iron- 
cored induction coil of the telephone transmitter, it was not possible 
to detect the presence or absence of high-frequency currents. 
As a test under severest conditions the effect was noted upon 
speech received at the same station at which the high-frequency 
current is being impressed, for here are the attenuated telephonic 
currents at the ‘receiving end of the telephone line, on which is super- 
imposed a high-frequency current of vastly greater magnitude at 
the same point. No effects of any kind could be detected under 
these conditions. From the above experiments it appears that in 
-any attempt at multiplex telephony by means of electric waves of 
ultra sound frequencies superimposed upon the minute telephonic 
currents employed in battery transmission there is nothing to fear 
from disturbances of such currents upon the operation of the ordinary 
battery equipment. 
Fig. 3. 
