ration. One of the most recent, and
we believe the most efficient so far developed, is the so-called
multiplex printer system, devised by the engineers of the Western
Union Telegraph Company and now being extensively used by that
company. Perhaps the best picture of what is accomplished by this
system can be given by an illustration. Let us assume a single wire
between New York and Chicago. At the New York end there are connected
with this wire four combined perforators and transmitters, and four
receiving machines operating on the typewriter principle. At the
Chicago end the wire is connected with a like number of sending and
receiving machines. All these machines are in simultaneous operation;
that is to say, four messages are being sent from New York to Chicago,
and four messages are being sent from Chicago to New York, all at the
same time and over a single wire, and the entire process is automatic.
The method by which eight messages can be sent over a single wire at
the same time without interfering with one another cannot readily
be described in simple terms. It may give some comprehension of the
underlying principle to say that the heart of the mechanism is in
two disks at each end of the line, which are divided into groups of
segments insulated from each other, each group being connected to one
of the sending or receiving machines, respectively. A rotating contact
brush connected to the line wire passes over the disk, so that, as it
comes into contact with each segment, the line wire is connected in
turn with the channel leading to the corresponding operating unit. The
brushes revolve in absolute unison of time and position. To use the
same illustration as before, the brush on the Chicago disk and the
brush on the New York disk not only move at exactly the same speed,
but at any given moment the two brushes are in exactly the same
position with regard to the respective group of segments of both
disks. If we now conceive of these brushes passing over the successive
segments of the disks at a very great rate of speed, it may be
understood that the effect is that the electrical impulses are
distributed, each receiving machine receiving only those produced by
the corresponding sending machine at the other end. In other words,
each of the sets of receiving and sending apparatus really gets the
use of the line for a fraction of the time during each revolution
of the brushes of the distributer or disk mechanism. The mul