, a small portable machine, or movement, for measuring time; having its motion commonly regulated by a spiral spring. Perhaps, strictly speaking, watches are all such movements as shew the parts of time; as clocks are such as publish them, by striking on a bell, &c. But commonly, the term Watch is appropriated to such as are carried in the pocket; and clock to the large movements, whether they strike the hour or not.

Spring or Pendulum Watches stand pretty much on the same principle with pendulum clocks. For if a pendulum, describing small circular arcs, make vibrations of unequal lengths, in equal times, it is because it describes the greater arc with a greater velocity; so a spring put in motion, and making greater and less vibrations, as it is more or less stiff, and as it has a greater or less degree of motion given it, performs them nearly in equal times. Hence, as the vibrations of the pendulum had been applied to large clocks, to rectify the inequality of their motions; so, to correct the unequal motions of the balance in Watches, a spring is added, by the isochronism of whose vibrations the correction is to be affected. The spring is usually wound into a spiral; that, in the little compass allotted it, it may be as long as possible; and may have strength enough not to be mastered, and dragged about, by the inequalities of the balance it is to regulate. The vibrations of the two parts, viz, the spring and the balance, should be of the same length; but so adjusted, as that the spring, being more regular in the length of its vibrations than the balance, may occasionally communicate its regularity to the latter.

The Invention of Spring or Pocket Watches, is due to the last age. It is true, it is said, in the history of Charles the 5th, that a Watch was presented to that prince: but this was probably no more than a kind of clock to be set on a table: some resemblance of which we have still remaining in the ancient pieces made before the year 1670. Some accounts also say, the first Watches were made at Nuremberg in 1500, by Peter | Hell, and were called Nuremberg eggs, on account of their oval form. And farther, that the same year George Purbach, a mathematician of Vienna, employed a watch that pointed to seconds, for astronomical observations, which was probably a kind of clock. In effect, it is between Hook and Huygens that the glory of this excellent invention lies: but to which of them it properly belongs, has been greatly disputed; the English ascribing it to the former, and the French, Dutch, &c, to the latter. Derham, in his Artificial Clockmaker, says roundly, that Dr. Hook was the inventor; and adds, that he contrived various ways of regulation: one way was with a loadstone: another with a tender straight spring, one end of which played backward and forward with the balance; so that the balance was to the spring as the ball of a pendulum, and the spring as the rod of the same: a third method was with two balances, of which there were divers sorts; some having a spiral spring to the balance for a regulalator, and others without. But the way that prevailed, and which still continues in mode, was with one balance, and one spring running round the upper part of the verge of it: though this has a disadvantage, which those with two springs &c were free from; in that, a sudden jerk, or confused shake will alter its vibrations, and flurry it very much.

The time of these inventions was about the year 1658; as appears, among other evidences, from an inscription on one of the double-balance Watches presented to king Charles the second, viz, Rob. Hook inven. 1658. T. Tompion fecit, 1675. The invention soon came into repute both at home and abroad; and two of the machines were sent for by the Dauphin of France. Soon after this, M. Huygens's Watch with a spiral spring got abroad, and made a great noise in England, as if the longitude could be found by it. It is certain however, that this invention was later than the year 1673, when his book De Horol. Oscillat. was published; in which there is no mention of this, though he speaks of several other contrivances in the same way.

One of these the lord Brounker sent for out of France, where M. Huygens had got a patent for them. This Watch agreed with Dr. Hook's, in the application of the spring to the balance; only that of Huygens had a longer spiral spring and its pulses and beats were much slower; also the balance, instead of turning quite round, as Dr. Hook's, turned several times every vibration. Huygens also invented divers other kinds of Watches, some of them without any string or chain at all, which he called pendulum Watches.

Mr. Derham suggests that he suspects Huygens's fancy was first set to work by some intelligence he might have of Hook's invention from Mr. Oldenburg, or some other of his correspondents in England; though Mr. Oldenburg vindicates himself against that charge, in the Philos. Trans. numbers 118 and 129.

Watches, since their first invention, have gone on in a continued course of improvement, and they have lately been brought to great perfection, both in England and in France, but more especially the former, particularly owing to the great encouragement that has been given to them by the Board of Longitude. Some of the chief writers and improvers of Watches, are, Le Roy, Cummins, Harrison, Mudge, Emery, and Arnold, whose Watches are now in very high repute, and in frequent use in the navy and India ships, for keeping the longitude. See Derham's Artificial Clockmaker; Cummins's Principles of Clock and Watch work; Mudge's Thoughts on the Means of improving Watches, &c.

Striking Watches, are such as, besides the proper Watch part, for measuring time, have a clock part, for striking the hours, &c. These are real clocks; only moved by a spring instead of a weight; and are properly called pocket-clocks.

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, being 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 K. James the second's reign; when the ingenious inventor above mentioned was soliciting a patent for it. The talk of a patent engaged Mr. Quare to resume the thoughts of a like contrivance, which he 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 now is done by thrusting in the pendant itself) repeated both the hour and quarter with the same thrust.

Of the Mechanism of a Watch.

Watches, as well as clocks, are composed of wheels and pinions, with 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. Instead of a pendulum, therefore, they are obliged to use a balance (Pl. 34, fig. 4) to regulate the motion of a Watch; and of a spring (fig. 6), which serves instead 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. 5) is taken off. A is the barrel which contains the spring (fig. 6); the chain is rolled about the barrel, with one end of it fixed to the barrel A, and the other to the fusee B.

When a Watch is wound up, the chain which was upon the barrel winds about the susee, and by this means the spring is stretched; for the interior end of the spring is fixed by a spring to the immoveable 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 there 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 CC; 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 piece A, called the potance, and B called a follower, which are fixed on the plate fig. 5. 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. 7). This wheel acts upon the pallats of the verge 1, 2. (fig. 4) the axis of which carries the balance HH (fig. 4). The pivot I, in the end of the verge, enters into the hole G in the potance A (fig. 5). In this figure the pallats are represented; but the balance is on the other side of the plate, as may be seen in fig. 11. The pivot 3 of the balance enters into a hole of the cock BC (fig. 10), a perspective view of which is represented in fig. 12. Thus the balance, turns between the cock and the potance c (fig. 5), as in a kind of cage. The action of the balance-wheel upon the pallats 1, 2, (fig. 4) is the same with that of 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 pallat 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 depends not solely upon the action of the great spring, but chiefly upon the action of the spring abc, called the spiral spring (fig. 13) situated under the balance H, and represented in perspective (fig. 11); the exterior end of the spiral is fixed to the pin a (fig. 13). This pin is applied near the plate in a (fig. 11); the interior end of the spiral is fixed by a peg to the centre of the balance. Hence if the balance be turned upon itself, the plates remaining immoveable, 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. 7 all the wheels above described are represented in such a manner, that we may easily perceive at first sight how the motion is communicated from the barrel to the balance.

In fig. 8 are represented the wheels under the dialplate, by which the hands are moved. The pinion a is adjusted to the force of the prolonged pivot of the wheel D (fig. 7), 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. 8) is indented into the wheel b, which is carried by the pinion a. Fig. 9 is a wheel fixed upon a barrel, into the cavity of which the pinion a enters, and upon which it turns freely. This wheel d revolves in 12 hours, and carries along with it the hour-hand.

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Entry taken from A Mathematical and Philosophical Dictionary, by Charles Hutton, 1796.

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WALLIS (Dr. John)
WARD (Dr. Seth)