send, therefore, three impulses over the line.
These impulses will act on the vertical magnet of the first selector
switch to move it up three steps. On this "level" of the contact bank of
this switch all of the contacts will represent second selector trunks
leading to the _third_ thousand group. The other ends of these trunks
will terminate in the wipers and also in the controlling magnets of
second selectors serving this thousand. This function on the part of the
first selector controlled by the act of the subscriber will have thus
selected a _group_ of trunks leading to the _third_ thousand, but the
subscriber has nothing to do with which one of the trunks of this group
will actually be used. Immediately following the vertical movement of
the first selector switch the rotary movement of this switch will start
and will continue until the wipers of that switch have found contacts of
an idle trunk leading to a second selector. Assuming that the first
trunk was the one found idle, the first selector wipers would pause on
the first pair of contacts in the third level of its bank, and the trunk
chosen may be seen leading from that contact off to the group of second
selectors belonging to the third thousand. For clearness, the chosen
trunks in this assumed connection are shown heavier than the others.

_Second Selector Action._ The next movement of the dial by the
subscriber in establishing his desired connection will send two
impulses, it being desired to choose the _second_ hundred in the _third_
thousand. The first selector will have become inoperative before this
second series of impulses is sent and, therefore, only the second
selector will respond. Its vertical magnet acting under the influence of
these two impulses will step up its wiper contacts opposite the second
row of bank contacts, and the subscriber will thus have chosen the
_group_ of trunks leading to the _second_ hundred in the _third_
thousand. Here, again, the automatic operation of picking out the first
idle one of this chosen group of trunks will take place without the
volition of the subscriber, and it will be assumed that the first two
trunks on this level of the second selector were found already engaged
and that the third was therefore chosen. The connection continues, as
indicated by heavy lines in Fig. 381, to the third one of the connectors
in the _second_ hundred of the _third_ thousand. Any one of these
connectors would have accomplished the pur