or where the spring S acts upon it is such that the spring both
drives the hammer against the bell when the tail T is raised, and also
checks it just before it reaches the bell, the blow on the bell thus
being given by the hammer having acquired momentum enough to go a little
farther than its place of rest. Sometimes two springs are used, one for
impelling the hammer, and the other for checking it. But nothing will
check the chattering of a heavy hammer, except making it lean forward so
as to act, partially at least, by its weight. The pinion of the
striking-wheel generally has eight leaves, the same number as the pins;
and as a clock strikes 78 blows in 12 hours, the great wheel will turn
in that time if it has 78 teeth instead of 96, which the great wheel of
the going part has for a centre pinion of eight. The striking-wheel
drives the wheel above it once round for each blow, and that wheel
drives a fourth (in which there is a single pin P), six, or any other
integral number of turns, for one turn of its own, and that drives a
fan-fly to moderate the velocity of the train by the resistance of the
air, an expedient at least as old as De Vick's clock in 1379.

The wheel N is so adjusted that, within a few minutes of the hour, the
pin in it raises the _lifting-piece_ LONF so far that that piece lifts
the click C out of the teeth of the _rack_ BKRV, which immediately falls
back (helped by a spring near the bottom) as far as its tail V can go by
reason of the snail Y, against which it falls; and it is so arranged
that the number of teeth which pass the click is proportionate to the
depth of the snail; and as there is one step in the snail for each hour,
and it goes round with the hour-hand, the rack always drops just as many
teeth as the number of the hour to be struck. This drop makes the noise
of "giving warning." But the clock is not yet ready to strike till the
lifting piece has fallen again; for, as soon as the rack was let off,
the tail of the _gathering pallet_ G, on the prolonged arbor of the
third wheel, was enabled to pass the pin K of the rack on which it was
pressing before, and the striking train began to move; but before the
fourth wheel had got half round, its pin P was caught by the end of the
lifting-piece, which is bent back and goes through a hole in the plate,
and when raised stands in the way of the pin P, so that the train cannot
go on till the lifting-piece drops, which it does exactly at the hour,
by