es of advantage,
one of which is a great simplification and reduction in size of the
subscriber's station signal-transmitting apparatus.

With the doing away of the ground as a return circuit, it becomes
impossible to send vertical impulses over one side of the line and to
follow them by single rotary impulses over the other side of the line.
Yet it becomes necessary to distinguish between the pure selective
impulses and those impulses which dictate a change of function at the
central office. The plan has, therefore, been adopted of accomplishing
the selection in each case by short and rapidly recurring impulses and
of accomplishing those functions formerly brought about by the single
impulse over the rotary side of the line by a pause between the
respective series of selective impulses. This is accomplished at the
central office by replacing the vertical and the rotary relays of the
three-wire system by a quick-acting and a sluggish relay, respectively;
the quick-acting relay performing the functions previously carried out
by the vertical relay, and the sluggish relay acting only during the
pauses between the successive series of quick impulses to do the things
formerly done by the rotary relay. This has resulted in a delightful
simplification of subscriber's apparatus, since it is now necessary only
to provide a device which will connect the two sides of the line
together the required number of times in quick succession and then allow
a pause with the circuit closed while the subscriber is getting ready to
transmit another set of impulses corresponding to another digit. The
calling device has no mechanical function co-acting with any of the
other parts of the telephone and may be considered as a separate
mechanical device electrically connected with the line. The transmitting
device is not much larger than a large watch and a good idea of it may
be had from Fig. 399, which shows the latest wall set, and Fig. 400,
which shows the latest desk set of the Automatic Electric Company. We
regret the fact that this company has made the request that the complete
details of their two-wire system be not published at this time.

[Illustration: Fig. 400. Desk Stand for Two-Wire System]

CHAPTER XXX

THE LORIMER AUTOMATIC SYSTEM

The Lorimer automatic telephone system has not been commercially used in
this country but is in commercial operation in a few places in Canada.
It is interesting from several points of view. I