a machine constructed in such a manner, and regulated by such uniform movements, as to measure time, and all its subdivisions, with great exactness.
The invention of clocks with wheels is referred to Pacificus, archdeacon of Verona, who lived in the time of Lotharius son of Louis the Debonair, on the credit of an epitaph quoted by Ughelli, and borrowed by him from Panvinius. They were at first called nocturnal dials, to distinguish them from sun-dials, which showed the hour by the sun's shadow. Others ascribe the invention to Boethius, about the year 510. Mr Derham makes clock-work of a much older standing; and ranks Archimedes's sphere mentioned by Claudian, and that of Posidonius mentioned by Cicero, among the machines of this kind: not that either their form or use were the same with those of ours, but that they had their motion from some hidden weights or springs, with wheels, or pulleys, or some such clockwork principle. But be this as it will, it is certain the art of making clocks, such as are now in use, was either first invented, or at least retrieved, in Germany, about 200 years ago. The water-clocks, or clepsydrae, and sun-dials, have both a much better claim to antiquity. The French annals mention one of the former kind lent by Aaron, king of Persia, to Charlemagne, about the year 807, which seemed to bear some resemblance to the modern clocks: it was of brass, and showed the hours by twelve little balls of the same metal, which fell at the end of each hour, and in falling struck a bell and made it sound. There were also figures of 12 cavaliers, which at the end of each hour came forth at certain apertures or windows in the side of the clock, and shut them again, &c.
The invention of pendulum-clocks is owing to the happy industry of the last age: the honour of it is disputed by Huygens and Galileo. The former, who has written a volume on the subject, declares it was first put into practice in the year 1657, and the description thereof printed in 1658. Becher, de Nova Temporis Divisioni Theoria, anno 1680, flicks for Galileo; and relates, though at second-hand, the whole history of the invention; adding, that one Treiler, clock-maker to the then father of the grand-duke of Tuscany, made the first pendulum-clock at Florence, by direction of Galileo Galilei; a pattern of which was brought into Holland. The academy de Cimento say expressly, that the application of the pendulum to the movement of a clock was first proposed by Galileo, and first put into practice by his son Vincenzo Galilei, in 1649. Be the inventor who he will, it is certain the invention never flourished till it came into Huygens's hands, who insists on it, that if ever Galileo thought of such a thing, he never brought it to any degree of perfection. The first pendulum-clock made in England, was in the year 1622, by Mr Fromantil a Dutchman.
Amongst the modern clocks, those of Strasbourg and Lyons are very eminent for the richness of their furniture, and the variety of their motions and figures. In the first, a cock claps his wings, and proclaims the hour; the angel opens a door, and salutes the virgin; and the holy Spirit descends on her, &c. In the second, two horsemen encounter, and beat the hour on each other: a door opens, and there appears on the theatre the virgin, with Jesus Christ in her arms; the magi, with their retinue, marching in order, and presenting their gifts; two trumpeters, sounding all the while to proclaim the procession. These, however, are excelled by two lately made by English artists, and intended as a present from the East India company to the emperor of China. The clocks we speak of are in the form of chariots, in which are placed, in a fine attitude, a lady, leaning her right hand upon a part of the chariot, under which is a clock of curious workmanship, little larger than a shilling, that strikes and repeats, and goes eight days. Upon her finger sits a bird finely modelled, and set with diamonds and rubies, with its wings expanded in a flying posture, and actually flutters for a considerable time on touching a diamond button below it; the body of the bird (which contains part of the wheels that in a manner give life to it) is not the bigness of the 16th part of an inch. The lady holds in her left hand a gold tube not much thicker than a large pin, on the top of which is a small round box, to which a circular ornament set with diamonds not larger than a sixpence is fixed, which goes round near three hours in a constant regular motion. Over the lady's head, supported by a small fluted pillar no bigger than a quill, is a double umbrella, under the largest of which a bell is fixed at a considerable distance from the clock, and seems to have no connection with it; but from which a communication is secretly conveyed to a hammer, that regularly strikes the hour, and repeats the same at pleasure, by touching a diamond button fixed to the clock below. At the feet of the lady is a gold dog; before which from the point of the chariot are two birds fixed on spiral springs; the wings and feathers of which are let with bones of various colours, and appear as if flying away with the chariot, which, from another secret motion, is contrived to run in a straight, circular, or any other direction; a boy that lays hold of the chariot behind, seems also to push it forward. Above the umbrella are flowers, and ornaments of pearls, rubies, and other precious stones; and it terminates with a flying dragon set in the same manner. The whole is of gold, most curiously executed, and embellished with gold, rubies, and pearls.
Of the Mechanism of Clocks, and how they measure Time. The first figure of Plate LXXX is a profile of a clock: P is a weight that is suspended by a rope that winds about the cylinder or barrel C, which is fixed upon the axis a a; the pivots b b go into holes made in the plates TS, TS, in which they turn freely. These plates are made of brass or iron, and are connected by means of four pillars ZZ; and the whole together is called the frame.
The weight P, if not restrained, would necessarily turn the barrel C with an uniform accelerated motion, in the same manner as if the weight was falling freely from a height. But the barrel is furnished with a ratchet wheel K K, the right side of whose teeth strikes against the click, which is fixed with a screw to the wheel D D, as represented in fig. 2, so that the action of the weight is communicated to the wheel D D, the teeth of which act upon the teeth of the small wheel d which turns upon the pivots c c. This communication of the teeth of one wheel with another, is called engrenage or pitching; and a small wheel, like d, is called a pinion.
The wheel E E is fixed upon the axis of the pinion d; and the motion communicated to the wheel D D by the weight is transmitted to the pinion d, consequently to the wheel E E, as likewise to the pinion f, and wheel F F, which moves the pinion f, upon the axis of which the crown or balance wheel G H is fixed. The pivots of the pinion f play in holes of the plates L M which are fixed horizontally to the plates T S. In a word, the motion begun by the weight is transmitted from the wheel G H to the pallettes I K, which communicates its motion, by means of the fork U X riveted on the pallettes, to the pendulum A B, which is suspended upon the hook A. The pendulum A B describes, round the point A, an arc of a circle alternately going and returning. If then the pendulum be once put in motion by a pull of the hand, the weight of the pendulum at B will make it return upon itself, and it will continue to go alternately backward and forward till the resistance of the air upon the pen- dulum, and the friction at the point of suspension at A, destroys the original impressed force. But as, at every vibration of the pendulum, the teeth of the balance-wheel G H act upon the palettes I K, (the pivots upon the axis of these palettes play in two holes of the potence s t,) that after one tooth H has communicated motion to the palette K, that tooth escapes; then the opposite tooth G acts upon the palette I, and escapes in the same manner; and thus each tooth of the wheel escapes the palettes I K, after having communicated their motion to the palettes in such a manner that the pendulum, instead of being stopped, continues to move.
The wheel E E revolves in an hour; the pivot e of this wheel passes through the plate, and is continued to r; upon the pivot is a wheel N N with a long socket fastened in the centre; upon the extremity of this socket r the minute-hand is fixed. The wheel N N acts upon the wheel O; the pinion of which, p, acts upon the wheel g g, fixed upon a socket which turns along with the wheel N. This wheel g g makes its revolution in 12 hours, upon the barrel of which the hour-hand is fixed.
From the above description it is easy to see, 1. That the weight p turns all the wheels, and at the same time continues the motion of the pendulum. 2. That the quickness of the motion of the wheels is determined by that of the pendulum. 3. That the wheels point out the parts of time divided by the uniform motion of the pendulum.
When the cord upon which the weight is suspended is entirely run down from off the barrel, it is wound up again by means of a key, which goes on the square end of the arbor at Q, by turning it in a contrary direction from that in which the weight descends. For this purpose, the inclined side of the teeth of the wheel R (fig. 2.) removes the click C, so that the ratchet-wheel R turns while the wheel D is at rest; but as soon as the cord is wound up, the click falls between the teeth of the wheel D, and the right side of the teeth again act upon the end of the click, which obliges the wheel D to turn along with the barrel; and the spring A keeps the crank between the teeth of the ratchet-wheel R.
We shall now explain how time is measured by the motion of the pendulum; and how the wheel E, upon the axis of which the minute-hand is fixed, makes but one precise revolution in an hour. The vibrations of a pendulum are performed in a shorter or longer time in proportion to the length of the pendulum itself. A pendulum of 3 feet 8 French lines in length, makes 3600 vibrations in an hour; i.e., each vibration is performed in a second of time, and for that reason it is called a second pendulum. But a pendulum of 9 inches 2 French lines makes 7200 vibrations in an hour, or two vibrations in a second of time, and is called a half-second pendulum. Hence, in constructing a wheel whose revolution must be performed in a given time, the time of the vibrations of the pendulum which regulates its motion must be considered. Supposing, then, that the pendulum AB makes 7200 vibrations in an hour, let us consider how the wheel E shall take up an hour in making one revolution. This entirely depends on the number of teeth in the wheels and pinions. If the balance-wheel consists of 30 teeth, it will turn once in the time that the pendulum makes 60 vibrations: for at every turn of the wheel, the same tooth acts once on the palette I, and once on the palette K, which occasions two separate vibrations in the pendulum; and the wheel having 30 teeth, it occasions twice 30, or 60 vibrations. Consequently, this wheel must perform 120 revolutions in an hour; because 60 vibrations, which it occasions at every revolution, are contained 120 times in 7200, the number of vibrations performed by the pendulum in an hour. Now, in order to determine the number of teeth for the wheels E F, and their pinions e f, it must be remarked, that one revolution of the wheel E must turn the pinion e as many times as the number of teeth in the pinion is contained in the number of teeth in the wheel. Thus, if the wheel E contains 72 teeth, and the pinion e 6, the pinion will make 12 revolutions in the time that the wheel makes 1; for each tooth of the wheel drives forward a tooth of the pinion, and when the 6 teeth of the pinion are moved, a complete revolution is performed; but the wheel E has by that time only advanced 6 teeth, and has still 66 to advance before its revolution be completed, which will occasion 11 more revolutions of the pinion. For the same reason, the wheel F having 60 teeth, and the pinion f 6, the pinion will make 10 revolutions while the wheel performs one. Now, the wheel F being turned by the pinion e, makes 12 revolutions for one of the wheel E; and the pinion f makes 10 revolutions for one of the wheel F; consequently, the pinion f performs 10 times 12 or 120 revolutions in the time the wheel E performs one. But the wheel G, which is turned by the pinion f, occasions 60 vibrations in the pendulum each time it turns round; consequently the wheel G occasions 60 times 120 or 7200 vibrations of the pendulum while the wheel E performs one revolution; but 7200 is the number of vibrations made by the pendulum in an hour, and consequently the wheel E performs but one revolution in an hour; and so of the rest.
From this reasoning, it is easy to discover how a clock may be made to go for any length of time without being wound up: 1. By increasing the number of teeth in the wheels. 2. By diminishing the number of teeth in the pinions. 3. By increasing the length of the cord that suspends the weight; and lastly, by adding to the number of wheels and pinions. But, in proportion as the time is augmented, if the weight continues the same, the force which it communicates to the last wheel G H will be diminished.
It only remains to take notice of the number of teeth in the wheels which turn the hour and minute hands.
The wheel E performs one revolution in an hour; the wheel N N, which is turned by the axis of the wheel E, must likewise make only one revolution in the same time; and the minute-hand is fixed to the barrel of this wheel. The wheel N has 30 teeth, and acts upon the wheel O, which has likewise 30 teeth, and the same diameter; consequently the wheel O takes one hour to a revolution; now the wheel O carries the pinion p, which has 6 teeth, and which acts upon the wheel gg of 72 teeth; consequently the pi- CLO
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CLO
Cloth
makes 12 revolutions while the wheel gg makes one, and of course the wheel gg takes 12 hours to one revolution; and upon the barrel of this wheel the hour-hand is fixed. We shall conclude with remarking, that all that has been said here concerning the revolutions of the wheels, &c., is equally applicable to watches as to clocks. See the article WATCH, to which the other figures on the plate relate.