nd a strip of ten jacks in Fig. 251. In such a
strip of jacks, the strips supporting the metallic parts of the
various jacks are usually of hard rubber reinforced by brass so as to
give sufficient strength. Various forms of supports for these strips
are used by different manufacturers, the means for fastening them in
the switchboard frame usually consisting of brass lugs on the end of
the jack strip adapted to be engaged by screws entering the stationary
portion of the iron framework; or sometimes pins are fixed in the
framework, and the jack is held in place by nuts engaging
screw-threaded ends on such pins.

[Illustration: Fig. 250. Individual Jack]

[Illustration: Fig. 251. Strip of Jacks]

_Methods of Associating Jacks and Drops._ There are two general
methods of arranging the drops and jacks in a switchboard. One of
these is to place all of the jacks in a group together at the lower
portion of the panel in front of the operator and all of the drops
together in another group above the group of jacks. The other way is
to locate each jack in immediate proximity to the drop belonging to
the same line so that the operator's attention will always be called
immediately to the jack into which she must insert her plug in
response to the display of a drop. This latter practice has several
advantages over the former. Where the drops are all mounted in one
group and the jacks in another, an operator seeing a drop fall must
make mental note of it and pick out the corresponding jack in the
group of jacks. On the other hand, where the jacks and drops are
mounted immediately adjacent to each other, the falling of a drop
attracts the attention of the operator to the corresponding jack
without further mental effort on her part.

The immediate association of the drops and jacks has another
advantage--it makes possible such a mechanical relation between the
drop and its associated jack that the act of inserting the plug into
the jack in making the connection will automatically and mechanically
restore the drop to its raised position. Such drops are termed
_self-restoring drops_, and, since a drop and jack are often made
structurally a unitary piece of apparatus, they are frequently called
_combined_ drops and jacks.

_Manual vs. Automatic Restoration._. There has been much difference of
opinion on the question of manual versus automatic restoration of
drops. Some have contended that there is no advantage in having the
drops res