without his volition, starts to pick out
the first idle one of the group of trunks so chosen. Having found this
it connects with it and the calling subscriber's line is thus extended
to another selective apparatus capable of performing the same sort of
function in choosing the proper hundreds group.

In the next movement of his dial the calling subscriber will send five
impulses. This will cause the last chosen selective switch to move its
selective fingers opposite a group of terminals representing the ends of
a group of trunks each leading to a switch that is capable of making
connection with any one of the lines in the fifth hundred of the ninth
thousand. Again during the pause by the subscriber, the switch that
chose this group of trunks will start automatically to pick out and
connect with the first idle one of them, and will thus extend the line
to a selective switch that is capable of reaching the desired line,
since it has access to all of the lines in the chosen hundred. The third
movement of the dial sends six impulses and this causes this last chosen
switch to move opposite the sixth group of ten terminals, so that there
has now been chosen the nine hundred and fifty-sixth group of ten lines.
The final movement of the dial sends seven impulses and the last
mentioned switch connects with the seventh line terminal in the group of
ten previously chosen and the connection is complete, assuming that the
called line was not already engaged. If it had been found busy, the
final switch would have been prevented from connecting with it by the
electrical condition of certain of its contacts and the busy signal
would have been transmitted back to the calling subscriber.

_Fundamental Idea._ This idea of subdividing the subscribers' lines in
an automatic exchange, of providing different groups of trunks so
arranged as to afford by combination a number of possible parallel paths
between any two lines, of having the calling subscriber select, by the
manipulation of his instrument, the proper group of trunks any one of
which might be used to establish the connection he desires, and of
having the central-office apparatus act automatically to choose and
connect with an idle one in this chosen group, should be firmly grasped.
It appears, as we have said, in every successful automatic system
capable of serving more than one small group of lines, and until it was
evolved automatic telephony was not a success.

_Testing._ As e