lling subscriber are continued by the levers _1_ and _2_ of
the side switch through the vertical and the rotary relay coils,
respectively, to the live side of battery. The lever _4_ of the side
switch in this position connects to ground the circuit leading from the
line switch through the release trunk, and the winding of the off-normal
relay. This winding is thus put in series with the release magnet of
the line switch, but on account of high resistance of the off-normal
relay no operation of the release magnet is caused. This will, however,
permit such current to flow through the release circuit as will energize
the sensitive off-normal relay and cause it to attract its armature and
light the off-normal lamp. If this lamp remains lighted more than a
brief period of time, it will attract notice and will indicate that the
corresponding selector has been appropriated by a line switch and that
for some reason the selector has gone no further. This lamp, therefore,
is an aid in preventing the continuance of this abnormal condition.

The first thing that happens after the line switch has connected the
calling subscriber with the first selector is a succession of impulses
over the vertical side of the line, this being the set of impulses
corresponding in number to the thousands digit or to the office, if
there is more than one. It will be understood that here we are
considering a single office of ten-thousand-line capacity or
thereabouts, and that, therefore, this first set of impulses corresponds
to the thousands digit in the called subscriber's line. Each one of
these impulses will flow from the battery through the vertical relay and
each movement of this relay armature will close the circuit of the
vertical magnet and cause the shaft of the selector to be stepped up to
the proper level. Immediately following the first series of selecting
impulses from the subscriber's station, a single impulse follows over
the rotary side of the line. This gives the rotary relay armature one
impulse and this in turn closes the circuit of the private magnet once.
The single movement of the private magnet armature allows the escapement
finger on the arm _5_ to move one step and this brings the side switch
contacts into the second position.

_Second Position of Side Switch._ In this position lever _4_ of the side
switch places a ground on the wire leading through the rotary magnet to
a source of interrupted battery current. The impulses whic