ator presses one of these dot keys, it is engaged by an
appropriate pin on the revolving cylinder. Meanwhile the type-wheels are
rotating, carrying with them the rocking-lever, and current is pulsating
over both circuits. When the type-wheels have arrived at the proper
point the rocking-lever has been carried to a position where its lower
arm is directly over one of the pins on the arm extending from the
platen of the press-lever. The cylinder stops, and current operates
the sluggish press-magnet, causing its armature to be attracted, thus
lifting the platen and its projecting arm. As the arm lifts upward, the
pin moves along the under side of the lower arm of the rocking-lever,
thus causing it to cant and shift the type-wheels to the right or left,
as desired. The principles of operation of this apparatus have been
confined to a very brief and general description, but it is believed to
be sufficient for the scope of this article.

NOTE.--The illustrations in this article are reproduced from American
Telegraphy and Encyclopedia of the Telegraph, by William Maver, Jr., by
permission of Maver Publishing Company, New York.

II. THE QUADRUPLEX AND PHONOPLEX

EDISON'S work in stock printers and telegraphy had marked him as a
rising man in the electrical art of the period but his invention of
quadruplex telegraphy in 1874 was what brought him very prominently
before the notice of the public. Duplex telegraphy, or the sending of
two separate messages in opposite directions at the same time over
one line was known and practiced previous to this time, but quadruplex
telegraphy, or the simultaneous sending of four separate messages,
two in each direction, over a single line had not been successfully
accomplished, although it had been the subject of many an inventor's
dream and the object of anxious efforts for many long years.

In the early part of 1873, and for some time afterward, the system
invented by Joseph Stearns was the duplex in practical use. In April of
that year, however, Edison took up the study of the subject and filed
two applications for patents. One of these applications [23] embraced
an invention by which two messages could be sent not only duplex, or
in opposite directions as above explained, but could also be sent
"diplex"--that is to say, in one direction, simultaneously, as separate
and distinct messages, over the one line. Thus there was introduced a
new feature into the art of multiplex telegraphy