CLOCK. 
back plate of the clock’s frame, and carry- 
ing a long lever f; this lever lias a small 
pin projecting from its lower end, going in- 
to an oblong hole, made in the rod B of 
the pendulum. The pendulum consists of 
an inflexible metallic rod, suspended by a 
very slender piece of steel-spring, D, from 
a brass bar, E, screwed to the fmme of the 
clock, having a weight or bob at its lower 
end, in the present case 39.125 inches 
from the suspension D ; when this pen- 
dulum is moved from the perpendicular 
line in either direction, and suffered to 
fall back again, it swings nearly as imich 
beyond the perpendicular on the contrary 
side, and then returns ; this it will continue 
to do for some time, and each of these vi- 
brations will be performed in one second 
of time when the pendulum is of the above 
length. This is the measurer of the time; and 
the oflfce of the clock is only to indicate 
the number of vibrations it has made, and 
give it a small impulse each time to keep it 
going, as the resistance of the ah- and elastici- 
ty of the spring D would otherwise in a few 
hours cause it to stop. By the action of the 
weight applied to the cord h, (which is called 
the maintaining power), the wheels are all 
turned round, and if the pallets d h were re- 
moved, the swing wheel 30 would ■ revolve 
with great velocity in the direction from 30 
to (i, until the weight reached the ground ; the 
teeth of these pallets are so made that one 
of them always engages the wheel, and pre- 
vents it turning more than half a tooth at a 
time. In the drawing, the pallet d has the 
nearest tooth of tlie wheel resting on it, and 
the pendulum is on the side k of the per- 
pendicular; when it returns it moves the 
pallet d, so as to allow the tooth of the 
wheel to slip off ; but in the mean time the 
pallet h has interposed its point in the wav 
of the tooth next it, and stops the wheel 
till the next vibration or second ; the dis- 
tance between the two pallets d h is so ad- 
justed that only half a tooth of the wheel 
escapes at each vibration ; and as the wheel 
has 30 teeth, it w'ill revolve, once in 60 vi- 
brations of one second each, or one minute ; 
consequently a hand on the arbor of this 
wheel will indicate seconds pn the dial- 
plate F, a circle diyided into 60, the pi- 
nion of eight on its arbor is turned by a 
wheel of 60, which consequently wall turn 
once in seven turns and a half of the other 
or in seven minutes 30 seconds, or one-eighth 
of an hour j its pinion of eight is moved by a 
wheel of 64, or eight times itself, which 
will turn in one-eighth part of tlie time, this 
will be an hour j the arbor of this wheel 
therefore carries the minute hand of the 
clock. The great wheel of 96, being 12 
times the number of tlie pinion eight, will 
turn once in 12 hours, and the barrel a with 
it. The gut goes round 16 times, so that the 
clock will go eight days. The hour-hand 
of the clock is turned by the wheel-work 
shewn in fig. 3 : on the end of the arbor of 
the centre wheel 64 a tube is fitted, so as 
to go round with it by friction ; this carries 
the minute hand, but if the clock should re- 
quire correction, the hand may be slipped 
round witliout moving the wheels : this 
tube has a pinion of 40 teeth on its lower 
end, indicated hy a dotted circle ; this turns 
another wheel 40, of 40 teeth, which has a 
pinion of six teeth on its arbor, turning a 
wheel 72, of 72 teeth; the two wheels 40 
will both turn in an hour; and 72 in 12 
hours ; the arbor of this wheel has the hour- 
hand, and is a tube going over the arbor of 
the minute-hand, so that the two hands are 
concentric. The barrel a is fitted to an ar- 
bor coming through the plate of the clock, 
and is filed square to put on a key to wind 
up the weight; the great wheel 96 is not 
fixed fast to the arbor, but has a click on 
it, which takes the teeth of a rachet wheel 
cut upon the barrel ; so that the barrel may 
be turned in the direction to wind up the 
weight without the wheel ; but by the des- 
cent of tlie weight, the wheels will be turned 
by the click. 
Having now described the going part of 
the clock, it remains to describe the me- 
chanism by which the hours are struck. 
fig. 2, is a great wheel of 78 teetli, with 
a barrel and click tlie same as 96 ; it turns 
a pinion of eight ; 64 is a wheel on the same 
arbor, turning a pinion of eight on the 
arbor of the wheel o of 48, this turns an- 
other pinion of eight, and wheel p of 48, 
which turns a pinion of six, on the same 
arbor with a thin vane of metal, which is 
called the fly, and, by the resistance of the 
air to its motion, regulates the velocity of 
the wheels. The wheel 64 has eight pins 
projecting from it, these raise the tail n of 
the hammer, as they revolve ; the hammer 
is returned violently when the pins leave 
its tall, by aspring m pressing on the end 
of a pin put through its arbor, and strikes 
the bell, (the hammer and bell are behind 
the plate, and therefore unseen,) / is a 
short spring which the other end of tlie 
pin through the arbor touches, just before 
the hammer strikes the bell, its use is tq 
lift the hammer off the bell the instant i( 
