142 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911, 
purpose the twisted-pair telephone line was equipped with a com- 
plete standard local battery telephone set, as installed for commercial 
practice, and in addition one of the wires of the pair was equipped as 
in figure 1, the circuit beimg shown diagrammatically in figure 2. 
This particular arrangement was employed in this experiment for the 
reason that it was desired to have the battery telephone operate 
on its usual circuit with the introduction of ground connections 
at the ends of the 
BUREAU LaBorATORY line for the super- 
Be OF oe : 
SIGNAL corPs positionof the high- 
frequency circuit. 
When such ground 
connections were 
introduced directly 
without tuning ele- 
ge: io ments therein the 
metallic circuit ex- 
a perienced the usual 
disturbances found 
under city conditions, but the metallic circuit could be reduced to 
silence again by introducing in the ground connections the necessary 
tuning elements of magnitudes suited to wireless telegraphy. 
Next, the twisted-pair telephone line was equipped with a com- 
plete standard local battery telephone set, as installed for commercial 
practice, with the exception that the local battery circuit of the 
transmitter tele- : 
phone set was 
opened and a few NRRL LE eee ND. ve 
STANDARDS Sake parte See 
turns of coarse wire 
inserted in series 
with the two dry 
cells which are nor- 
mally used, as shown 
in figure 3. Induc- 
tively connected 
with this coil was 
the armature circuit 
of the generator. A hot wire milliammeter was placed in the line 
circuit to indicate the magnitude of the high-frequency current which 
was flowing on the line. With this arrangement tests were made to 
determine whether or not there were any effects upon the transmission 
of speech, due to superimposing high-frequency currents upon the 
‘battery telephone sets. With an operator at each end of the line, 
using the equipment in the regular commercial way, the direct-current 
voltage and the alternating-current voltage in series with it in the 
Fig. 2. 
