ns of sending more
messages over the wire in a given time. It will readily suggest
itself that the solution of this problem lies either in an arrangement
enabling the wire to carry more than one message at once, or in some
apparatus capable of transmitting messages over the wire more
rapidly than can be done by hand, or in a combination of both these
principles.

Duplex and quadruples operations are perhaps the most generally known
methods by which increased utilization of the capacity of the line has
been achieved. Duplex operation permits of the sending of two messages
over one wire in opposite directions at the same time; and quadruples,
the simultaneous transmission of four messages, two going in each
direction. Truly a remarkable accomplishment; but, like many other
things that have found their permanent place in daily use, become so
familiar that we no longer pause to marvel at it. These expedients
constitute a direct and very effective attack on the problem how to
get more work out of the wire with the existing means of operation,
and on account of their fundamental character and the important place
which by reason thereof they have taken in the telegraphic art, are
entitled to first mention.

The problem of increasing the rapidity of transmission has been met by
various automatic systems of telegraphy, so called because they embody
the idea of mechanical transmission with resulting gain in speed and
other advantages. The number of these which have from time to time
been devised is considerable. Not all have proven to be practicable,
but those which have failed to prove in under actual operating
conditions none the less display evidence of ingenuity which may well
excite our admiration.

To mention one or two which may be interesting on account of the
oddity of their method--there was, for instance, an early device,
similar in principle to the calling apparatus of the automatic
telephone, which involved the turning of a movable disk so that a
projection on its circumference pointed successively to the letters to
be transmitted. Experiments were made with ordinary metal type set up
in a composing-stick, a series of brushes passing over the type faces
and producing similar characters on a tape at the other end of the
line. In another more recent ingenious device a pivoted mirror at the
receiving end was so manipulated by the electrical impulses that a ray
of light reflected from the surface of the mirror actual