WATCH. 
«n the other side; tliis again alters the 
spring, which returns the balance, throwing 
it beyond the point of rest ;^and in this 
manner the balance will vibrate until the 
friction of the pivots and the resistance of 
the air destroys the original impulse. All 
vibrations of such a balance which pass 
through equal spaces will be performed in 
equal times. 
This simple apparatus is all which is re- 
quired for measuring time, the other mecha- 
nism of the watch being devoted to two 
objects: first, to give a small impulse to 
the balance at each vibration, to overcome 
the friction and resistance ot the air, and 
cause the balance to describe equal arcs : 
and, secondly, to register the number of 
vibrations the balance has made. 
The first of these objects requires a power 
which shall be in constant readiness to act 
upon the balance. TJiis is accomplished 
by the re-action of a spiral steel spring. A, 
(fig. 8) which when at rest and liberty as- 
sumes that position and size ; it is coiled up 
closer, and put into a brass box, a, called 
the spring barrel ; a small hook which is at 
the outer end of the spring being put 
through a hole in the side of the box, a 
small arbor, B, is put into the centre of the 
box, and the cover or lid of the box, D, is 
shut in : the arbor has a hook projecting 
from it, which enters a hole in the inner 
end of the spring A; its pivots project 
through the barrel at each side, and enter 
holes in the two plates E E, (fig. 5) which 
forms the frame of the watch ; the lower 
pivot passes through the plate, and has a 
small rachet wheel, b, (fig. 3 and 5) fixed 
upon it, a click entering the teeth thereof 
prevents the arbor turning roupd ; a small 
steel chain is hooked to the spring-barrel, a, 
(fig. 1 and 6) ; at one end it passes round 
the barrel several times, then round the 
fusee, d, and is hooked to it by its end. The 
fusee, d, is a conical piece of brass, with h 
spiral groove cut thereon to receive the' 
chain: it is mounted on pivots which turn 
in holes, in the two plates E E, and one of 
the pivots, e, projects a considerable dis- 
tance, and is cut square. Now if a key is 
applied to this square, and the fusee, d, by 
that meatis turned round so as to wind the 
chain upon it, the spring barrel will be 
turned round, and the outer end of the 
spring. A, being hooked to the barrel|will be 
turned round also; as the jnner end is im- 
moveable, by being fixed to the arbor-, B, 
the spring will be coiled up into a closer 
spiral than it was when at liberty, and will 
consequently exert a re-action upon the 
chain, and by that means upon the ftrsee, 
which will be turned rorrnd thereby when 
the key is removed. To prevent too much 
chain being wound upon the fusee, -and by 
that means breaking the chain, or over- 
straining the spring, a contrivance called a 
guard is added : it is a small lever, x (fig. 1) 
moving on a stud fixed to the upper plate 
of the watch, and pressed downwards by a 
small spring, z: as the chain is wound upon 
the fusee, it rises in the spiral groove, and 
lifts up the lever, x, until it touches the upper 
plate ; it is then in a position to intercept 
the edge of the spiral piece of metak seen ' 
on the top of the fusee, and thus stop it 
from being wound up any further. 
The power of the spring is transmitted to 
the balance by means of several cog wheels; 
the first, f, is upon the fusee ; it is shown 
separated from the fusee in fig. 6, having a 
hole through the centre to receive the arbor 
of the fusee, and a projecting ring upon its 
surface; the under surface of the fusee is 
shown in fig. 7, having a circular groove cut 
ill it to receive the corresponding ring upon 
the great wheek fig. 6 : the inner edge of 
the groove is cut with teeth to form a 
rachct wheel; when the whbel and fusee 
are put together, a small click, g, (fig. 6) 
takes into the teeth of the rachet: as the 
fusee is turned by the key, to wind up the 
watch, this click slips over the sloping sides 
of tlie teeth without turning the great wheel; 
but when the fusee, is turned the other way 
by the chain, the- click catches the teeth of 
the rachet wheel, and causes the cog wheel 
to turn with the fusee ; the great wheel, jf, 
h-as forty-eight teeth, and turns a pinion of 
twelve teeth on an arbor in the centre of 
the watch, which carries the minute hand : 
a ■p'heel, h, of fifty-four teeth, called the 
centre wheel, is fixed updn this arbor, and 
turns a pinion on the same arbor with 
the third wheel, k, of forty-eight teeth, 
which turns the pinion of the contrate 
wheel, i, of forty-eight teeth ; the contrate 
wheel gives motion to a pinion of six teeth, 
and to the balance wheel, m, whicii has fif- 
teen large teeth, which stop against two 
small pallets upon the arbor of the balance, 
or verge, r: these pallets are two small 
teeth, projecting from the verge at right 
angles to each other; one engages the up- 
per side of the wheel, and the other takes 
the lower. By the action of the main- 
spring, a, the wheels are all turned, and the 
