hat jack to
the spring _4_, and thence to ground and back to the other terminal of
the battery _7_.

_Magnet Windings._ Coils of the line and clearing-out drops by which
these drops are thrown, are wound to such high resistance and impedance
as to make it proper to leave them permanently bridged across the
talking circuit. The necessity for cutting them out is, therefore, done
away with, with a consequent avoidance, in the case of the line drops,
of the provision of series contacts in the jacks.

_Arrangement of Apparatus._ In boards of this type the line and
clearing-out drops were mounted in the extreme upper portion of the
switchboard face so as to be within the range of vision of the operator,
but yet out of her reach. Therefore, the whole face of the board that
was within the limit of the operator's reach was available for the
answering and multiple jacks. A front view of a little over one of the
sections of the switchboard, involving three complete operator's
positions, is shown in Fig. 339, which is a portion of the switchboard
installed by the Western Electric Company in one of the large exchanges
in Paris, France. (This has recently been replaced by a common-battery
multiple board.) In this the line drops may be seen at the extreme top
of the face of the switchboard, and immediately beneath these the
clearing-out drops. Beneath these are the multiple jacks arranged in
banks of one hundred, each hundred consisting of five strips of twenty.
At the extreme lower portion of the jack space are shown the answering
jacks and beneath these on the horizontal shelf, the plugs and keys.
These jacks were mounted on 1/2-inch centers, both vertically and
horizontally and each section had in multiple 90 banks of 100 each,
making 9,000 in all. Subsequent practice has shown that this involves
too large a reach for the operators and that, therefore, 9,000 is too
large a number of jacks to place on one section if the jacks are not
spaced closer than on 1/2-inch centers. With the jack involving as many
parts as that required by this branch terminal system, it was hardly
feasible to make them smaller than this without sacrificing their
durability, and one of the important features of the common-battery
multiple system which has supplanted this branch-terminal magneto system
is that the jacks are of such a simple nature as to lend themselves to
mounting on 3/8-inch centers, and in some cases on 3/10-inch centers.

[Illustration: