WAY DUPLEX SYSTEM.
A novel form of double transmission
was invented by the writer soon after the completion
of the harmonic system, and was an outgrowth of it.
It is still in use on some of the railroad-lines.
An ordinary railroad telegraph-line has an instrument
in circuit in every office along the road, chiefly
for purposes of train-dispatching. As we have
heretofore explained, whenever any one office is sending,
the dispatch is heard in all of the offices.
The “Way duplex” system permits of the
use of the line for through business simultaneously
with the operation of the local offices. That
is to say, any station along the line may be telegraphing
with any other station by the ordinary Morse method,
and at the same time messages may be passing back
and forth between the two end offices.
This is accomplished by the following
method: At each end of the line there is a tuned
reed, such as we have described in our last chapter,
that is kept constantly in vibration by a local battery
during working hours. This vibrator is so arranged
in relation to the battery that whenever the key belonging
to it is depressed the current all through the line
is rendered vibratory. There is also in circuit
at each end of the line a harmonic relay, that is
tuned in accord with the vibrating reed of the sender.
If either key belonging to this part of the system
is opened, as in the act of sending a message, these
harmonic relays, being tuned in sympathy with the
sending-vibrator, will respond, thus sending Morse
characters made up of a tone broken into dots and dashes.
This tone can be read directly from the relay, or,
as is usually the case, it causes the sounder to operate
in the common way.
You will at once inquire why the ordinary
Morse instruments in the local offices are not affected
by these vibratory signals, and also why the harmonic
instruments at the end office are not affected by the
working of the local offices. The local office
does not open the circuit entirely, but simply cuts
out a resistance by the operation of the special harmonic
key. When a resistance is thrown into an electric
circuit it weakens the current in proportion to the
amount of resistance interposed. You will see
that there is some current still left in the line
when the key is open, but the spring of the relay at
the local office is so adjusted as to pull the armatures
away from the magnets whenever the current is weakened
by throwing in the resistance, so that by this means
an ordinary Morse telegraphic relay may be worked without
ever entirely opening the circuit. In the Way
duplex system there is a resistance at each station
that is cut in and out by the operation of its key,
which causes all the instruments in the line to work
simultaneously except the two harmonic relays located
one at each end of the line. These will not respond
to anything but the vibratory signal.
In order to prevent the Morse relays
at the local offices from responding to the vibratory
current a condenser is connected around them.
This condenser serves two purposes: It enables
the short impulses of the vibrating current to pass
around the relays without having to be resisted by
the coils of the magnets, and between the pulsations
each condenser will discharge through the relay at
the local offices, and thus fill in the gap between
the pulsations, producing the effect on the relay
of a steady current. When a line is thus equipped
it may be treated in every respect as two separate
wires, one of them doing way business and the other
through business. It is a curious blending of
science and mechanism.
Another interesting application was
made of the system of transmission by musical tones by
Edison, some years ago. We refer to the transmission
of messages to and from a moving railroad-train with
the head office at the end of the line. In this
case the message was transmitted a part of the distance
through the air; another instance of wireless
telegraphy. The operation was as follows:
One of the wires strung on the poles nearest to the
track was fitted up with a vibrator and key at the
end of the line similar to that of the Way duplex just
described. In one of the cars was another battery,
key and vibrator, and as only one tone was used, no
tone-selecting device or harmonic relay was needed,
but instead an ordinary receiving-telephone was used
to read the long and short sounds sent over the lines.
One end of the battery in the car was connected through
the wheels to the earth, while the other end was connected
to the metal roof of the car. Being thus equipped,
we will suppose our train to be out on the road forty
or fifty miles from either end of the line, moving
at the rate of forty miles an hour. The operator
at Chicago, say, wishes to send a message to the moving
train; he operates his key in the ordinary manner,
which makes the current on the line vibratory during
the time the key is depressed. These electrical
vibrations cause magnetic vibrations, or ether-waves,
to radiate in every direction from the wire, at right
angles to the direction of the current, like rays
of light. When they strike the roof of the car
they create electrical impulses in the metal by induction
(described in Chap. VI). These impulses pass
through a telephone located in the car to the ground.
A Morse operator listening, with the telephone to
his ear, will hear the message through the medium of
a musical tone chopped up into the Morse code.
In like manner the operator in the car may transmit
a message to the roof of the car and thence through
the air to the wire, which will be heard, by any one
listening, in a telephone which is connected in that
circuit, and, as a matter of fact, it will
be heard from any wire that may be strung on any of
the poles on either side of the road.
Some years ago an experiment of this
kind was made on one of the roads between Milwaukee
and Chicago.
What wonderful things can be done
with electricity! As a servant of man it is reliable
and accurate seeming almost to have the
qualities of docility when under intelligent
direction, that is in accord with the laws of nature;
but under other conditions it changes from the willing
servant to a hard master, hesitating not to destroy
life or property without regard to persons or things.