MULTIPLEX TELEPHONY AND TELEGRAPHY—SQUIER. aS | 
employ telegraphy as a quick and ready means of determining 
resonance between the circuits in each particular case. 
When any particular arrangement was being employed the first 
steps were invariably to send simple Morse signals over the circuit 
until the operator at the distant end of the line reported maximum 
loudness in the receiving telephone, which indicated that the ter- 
minal apparatus with the line circuit was properly tuned. This 
being accomplished, it was necessary only to throw a switch to 
substitute for the automatic interrupter and telegraph key the 
telephone transmitter, and the experiments could then proceed on 
telephony without any material change being made at the receiving 
station. Telephony and telegraphy thus proceeded hand in hand 
as a mere matter of convenience, and one of the practical advantages 
in the use of electric waves for transmitting intelligence is that the 
whole set-up of apparatus is practically the same for each and they 
can be used interchangeably over the same circuit. 
Considering the Morse equipment, indicated in figure.8, the electro- 
magnetic units involved are of the order of magnitude of microfarads 
and henrys, and the period of the interrupted direct current for 
Morse sending is not more than the equivalent of about 10 complete 
cycles per second, whereas in the high-frequency side of the circuit 
the electromagnetic units are of the order of magnitude of thousandths 
of a microfarad and of thousandths of a henry and with frequencies 
not less than 2,000 times greater than those involved in manual 
Morse sending. Furthermore, the ohmic resistance of the line which 
plays a prominent part in limiting the distance and speed of Morse 
working, 1s comparatively unimportant in the case of electric waves 
euided by wires. The operation of the line equipped as in figure 8 
was perfectly satisfactory, there being no perceptible interference 
between the two messages in either direction. 
Since the standard telegraph circuits of the world use a ground 
return, this same equipment was arranged to operate on one of the 
wires of the twisted-pair in the telephone cable as such a circuit 
with earth connections at each end, and its operation was equally 
successful. 
Since it is a well-known characteristic of high-frequency apparatus 
used in tuned circuits that there shall be no iron involved in the 
circuit, it is evident that in cases where such a high-frequency cur- 
rent is to be superimposed upon a line comprising way stations, 
where line relays are inserted directly in the circuit, it will be neces- 
sary and sufficient to shunt such way stations by condensers of the 
order of magnitude of thousandths of a microfarad. Such con- 
densers offer a comparatively free path for the high-frequency electric 
waves, but interpose a practical barrier to the Morse frequencies. 
