ge the hour striking part as the fourth
quarter finishes.

But where the repetition movement is required for the quarters, the
matter is not quite so simple. The principle of it may shortly be
described thus. The quarters themselves have a rack and snail, &c., just
like the hours, except that the snail is fixed on one of the hour-wheels
M or N, instead of on the twelve-hour wheel, and has only four steps in
it. Now suppose the quarter-rack to be so placed that when it falls for
the fourth quarter (its greatest drop), it falls against the hour
lifting-piece somewhere between O and N, so as to raise it and the click
C. Then the pin Q will be caught by the click Qq, and so the
lifting-piece will remain up until all the teeth of the quarter-rack are
gathered up; and as that is done, it may be made to disengage the click
Qq, and so complete the letting off the hour striking part. This click
Qq has no existence except where there are quarters.

The method in which an alarum is struck may be understood by reference
to either of the recoil escapements (figs. 1 and 7). If a short hammer
instead of a long pendulum be attached to the axis of the pallets, and
the wheel be driven with sufficient force, it will evidently swing the
hammer rapidly backwards and forwards; and the position and length of
the hammer-head may be so adjusted as to strike a bell inside, first on
one side and then on the other. As to the mode of letting off the alarum
at the time required: if it was always to be let off at the same time
all that would be necessary would be to set a pin in the twelve-hour
wheel at the proper place to raise the lifting-piece which lets off the
alarum at that time. But as the time must be capable of alteration, this
discharging pin must be set in another wheel (without teeth), which
rides with a friction-spring on the socket of the twelve-hour wheel,
with a small movable dial attached to it, having figures so arranged
with reference to the pin that whatever figure is made to come to a
small pointer set as a tail to the hour hand, the alarum shall be let
off at that hour.

The _watchman's_ or _tell-tale_ clock, used when it is desired to make
sure of a watchman being on the spot and awake all the night, is a clock
with a set of spikes, generally 48 or 96, sticking out all round the
dial, and a handle somewhere in the case, by pulling which one of the
spikes which is opposite to it, or to some lever connected with it is
pressed