Repeating WATCHES, are such as by pulling a string, &c. repeat the hour, quarter, or minute, at any time of the day or night.—This repetition was the invention of Mr Barlow, and first put in practice by him in larger movements or clocks about the year 1676. The contrivance immediately set the other artists to work, who soon contrived divers ways of effecting the same. But its application to pocket-watches was not known before King James II.'s reign; when the ingenious inventor above mentioned, having directed Mr Thompson to make a repeating watch, was soliciting a patent for the same. The talk of a patent engaged Mr Quare to resume the thoughts of a like contrivance, which he had had in view some years before: he now effected it; and being pressed to endeavour to prevent Mr Barlow's patent, a watch of each kind was produced before the king and council; upon trial of which, the preference was given to Mr Quare's. The difference between them was, that Barlow's was made to repeat by pushing in two pieces on each side the watch-box; one of which repeated the hour, and the other the quarter: whereas Quare's was made to repeat by a pin that stuck out near the pendant, which being thrust in (as
Watch. now it is done by thrusting in the pendant itself, repeated both the hour and quarter with the same thrust.
Of the Mechanism of a WATCH, properly so called. Watches, as well as clocks, are composed of wheels and pinions, and a regulator to direct the quickness or slowness of the wheels, and of a spring which communicates motion to the whole machine. But the regulator and spring of a watch are vastly inferior to the weight and pendulum of a clock, neither of which can be employed in watches. In place of a pendulum, therefore, we are obliged to use a balance (fig. 1.) to regulate the motion of a watch; and a spring (fig. 2.) which serves in place of a weight, to give motion to the wheels and balance.
The wheels of a watch, like those of a clock, are placed in a frame formed of two plates and four pillars. Fig. 3. represents the inside of a watch, after the plate (fig. 4.) is taken off. A is the barrel which contains the spring (fig. 2.); the chain is rolled about the barrel, with one end of it fixed to the barrel A (fig. 5.), and the other to the fusee B.
When a watch is wound up, the chain which was upon the barrel winds about the fusee, and by this means the spring is stretched; for the interior end of the spring is fixed by a hook to the immovable axis, about which the barrel revolves; the exterior end of the spring is fixed to the inside of the barrel, which turns upon an axis. It is therefore easy to perceive how the spring extends itself, and how its elasticity forces the barrel to turn round, and consequently obliges the chain which is upon the fusee to unfold and turn the fusee; the motion of the fusee is communicated to the wheel C (fig. 5.); then, by means of the teeth, to the pinion c, which carries the wheel D; then to the pinion d, which carries the wheel E; then to the pinion e, which carries the wheel F; then to the pinion f, upon which is the balance-wheel G, whose pivot runs in the pieces A called the potance, and B called a follower, which are fixed on the plate fig. 4. This plate, of which only a part is represented, is applied to that of fig. 3. in such a manner that the pivots of the wheels enter into holes made in the plate fig. 3. Thus the impressed force of the spring is communicated to the wheels; and the pinion f being then connected to the wheel F, obliges it to turn (fig. 5.). This wheel acts upon the pallets of the verge, 1, 2, (fig. 1.), the axis of which carries the balance HH, (fig. 1.). The pivot I, in the end of the verge, enters into the hole c in the potance A (fig. 4.). In this figure the pallets are represented; but the balance is on the other side of the plate, as may be seen in fig. 6. The pivot 3 of the balance enters into a hole of the cock BC (fig. 7.), a perspective view of which is represented in fig. 8. Thus the balance turns between the cock and the potance c (fig. 4.), as in a kind of cage. The action of the balance-wheel upon the pallets 1, 2 (fig. 1.), is the same with what we have described with regard to the same wheel in the clock; i. e. in a watch, the balance-wheel obliges the balance to vibrate backwards and forwards like a pendulum. At each vibration of the balance a pallet allows a tooth of the balance-wheel to escape; so that the quickness of the motion of the wheels is entirely determined by the quickness of the vibrations of the balance; and these vibrations of the balance and motion of the wheels are produced by the action of the spring.
But the quickness or slowness of the vibrations of the
balance depend not solely upon the action of the great spring, but chiefly upon the action of the spring a, b, c, called the spiral spring (fig. 9.), situated under the balance H, and represented in perspective (fig. 6.). The exterior end of the spiral is fixed to the pin a, (fig. 9.) This pin is applied near the plate in a, (fig. 6.); the interior end of the spiral is fixed by a peg to the centre of the balance. Hence if the balance is turned upon itself, the plates remaining immovable, the spring will extend itself, and make the balance perform one revolution. Now, after the spiral is thus extended, if the balance be left to itself, the elasticity of the spiral will bring back the balance, and in this manner the alternate vibrations of the balance are produced.
In fig. 5. all the wheels above described are represented in such a manner, that you may easily perceive at first sight how the motion is communicated from the barrel to the balance.
In fig. 10. are represented the wheels under the dial-plate by which the hands are moved. The pinion a is adjusted to the force of the prolonged pivot of the wheel D (fig. 5.), and is called a cannon pinion. This wheel revolves in an hour. The end of the axis of the pinion a, upon which the minute-hand is fixed, is square; the pinion (fig. 10.) is indented into the wheel b, which is carried by the pinion a. Fig. 11. is a wheel fixed upon a barrel, into the cavity of which the pinion a enters, and upon which it turns freely. This wheel revolves in 12 hours, and carries along with it the hour-hand. For a full account of the principles upon which watches and all time-keepers are constructed, we must refer our readers to a short treatise, entitled Thoughts on the Means of improving Watches, by Thomas Mudge.