tides and two ebbs, consequently an error of three-quarters of an hour in each lunation will place the tide-plate H, three hours wrong in the space of about four months, and in nearly eight months an high water will be changed into low water, and the reverse in the next eight months, which is certainly an indispensable error. "That the clock-maker may not be at a loss how to apply the remedy we have proposed for the inaccuracy of Mr. Ferguson's solar and lunar wheels, we shall conclude our description of the clock before us with an account of the exact dimensions of the parts proposed to be substituted. If we take the wheel of communication of 37 teeth at 12 per inch, measured at the pitch line, its geometrical diameter will be 98 or of an inch, and is practical diameter, with the addendum for the ends of the teeth, 1-04; the wheel of 74 being double will have its geometrical diameter equal to 1-96, and its practical one 2·02; the fellow of this last or solar-wheel has its geometrical diameter by the same proportion, 1.14, and its practical che 1.20; the distance of the stud from the centre of motion of the solar and lunar wheels, must necessarily be the sum of the geometrical radii of thes two last wheels, namely, 1·96+1.14+2 which is 1·55; again the sum of the geometrical radii of the remaining two wheels, 32 and 57, must be also equal to 1:55, in order that the centres of motion of the solar and lunar wheels may exactly coincide; but a wheel of a geometrical diameter equal to 1.55 x 2 or 3.10 inches and of 32 +57 or 89 teeth, will have only about nine teeth per inch, and the practical diameters of wheels 32 and 57, by the same, will be respectively 1.21 and 2.1. The calliper suitable for these proportions and dimensions is given, of their full size and dimensions, in fig. 498, which needs no farther explanation, except that the wheels 43 and 32 are so nearly of a size that one circle represents both, as pinned together, and revolving with a contemporary motion round a stud or screw in their centre, going into the front plate of the clock-frame. The small wheel of 32 acts deeper into the teeth of its fellow than the 43, by reason of having larger teeth than the other, though the wheel is of the same size." In the year 1803, the Sciety for the Encouragement of Arts, &c. presented to Mr. John Prior, of Nessfield, Yorkshire, a reward of thirty guineas on account of his contrivance for the striking part of an eight-day clock. As this invention is likely to be useful we shall describe it here. It consists of a wheel and fly, with six turns of a spiral line, cut upon the wheel for the purpose of counting the hours. The pins below this spiral elevate the hammer, and those above are for the use of the detent. This single wheel serves the purpose of count-wheel, pin-wheel, detent-wheel, and the fly-wheel, and has six revolutions in striking the twelve hours. If we suppose a train of wheels and pinions used in other striking parts to be made without error, and that the wheels and pinions would turn each other without shake or play, then, allowing the above supposition to be true, (though every mechanic knows it is not,) Mr. Prior's striking part would be found six times superior to others, in striking the hours 1, 2, 5, 7, 10, 11; twelve times superior in striking 4, 6, 8; and eighteen times in striking 3 9, and 12. In striking 2, the inventor purposely made an imperfection equal to the space of three teeth of the wheel; and in striking 3, an imperfection of nine or ten teeth; and yet both these hours are struck perfectly correct. The flies in clocks turn round at a mean, about sixty times for every knock of the hamrier, but this turns round only three times for the same purpose: and suppose the pivots were of equal diameters, the influence of oil on them would be as the number of revolutions in each. It would be better for clocks if they gave no warning at all, but the snail piece to raise a weight somewhat similar to the model Mr. P. sent for the inspection of that respectable society. The striking part of this clock is represented in fig. 499. A, the large wheel, on the face of which are sunk or cut the six turns of a spiral. B, the single worm screw, which acts on the above wheel, and moves the fly C. D, the spiral work of the wheel A. The black spots show the grooves into which the detents drop on striking the hour. E, the groove into which the locking piece F drops when it strikes 1, and from which place it proceeds to the outward parts of the spiral in the progressive hours, being thrown out by a lifting piece H at each hour; the upper detent G being pumped off with the locking piece F, from the pins on the wheel A. In striking the hour of 12, the locking piece, having arrived at the outer spiral at H, rises up an inclined plane, and drops by its own weight into the inner circle, in which the hour 1 is to be struck, and proceeds on in a progressive motion through the different hours till it comes again to 12. I, the hammer-work made in the common way, which is worked by thirteen pins on the face of the spiral. Fig. 500, K, the thirteen pins on the face of the spiral, which work the hammer-work. L, the outer pins which lock the detent. In the fourth century, an artist named James Dondi constructed a clock for the city of Padua, which was long considered as the wonder of the period. Besides indicating the hours, it represented the motions of the sun, moon, and planets, as well as pointed out the different festivals of the year. On this account Dondi obtained the surname of Horologio, which became that of his posterity. A short time after, William Zelander constructed for the same city a clock still more complex; which was repaired in the sixteenth century by Janellin Turrianus, the mechanist of Charles V. But the clocks of the cathedrals of Strasburgh and of Lyons are much more celebrated. That of Strasburgh was the work of Conrad Dayspodius, a mathematician of that city, who finished it about 1573. The face of the basement of this clock exhibits three dial-plates; one of which is round, and consists of several concentric circles; the two interior ones of which perform their revolutions in a year, and serve to mark the days of the year, the festivals, and other circumstances of the calendar. The two lateral dial-plates are square, and serve to indicate the eclipses both of the sun and the moon. Above the middle dial-plate, and in the attic space of the basement, the days of the week are represented by different divinities, supposed to preside over the planets from which their common appellations are derived. The divinity of the current day appears in a car rolling over the clouds, and at midnight retires to give place to the succeeding one. Before the basement is seen a globe borne on the wings of a pelican, around which the sun and moon revolved; and which in that manner represented the motion of these planets, but this part of the machine, as well as several others, has been deranged for a long time. The ornamental turret, above this basement, exhibits chiefly a large dial in the form of an astrolabe; which shows the annual motion of the sun and moon through the ecliptic, the hours of the day, &c. The phases of the moon are seen also marked out on a particular dialplate above. This work is remarkable also for a considerable assemblage of bells and figures, which perform different motions. Above the dial-plate last mentioned, for example, the four ages of man are represented by symbolical figures: one passes every quarter of an hour, and marks the quarter by striking on small bells; these figures are followed by Death, who is expelled by Jesus Christ risen from the grave: who, however, permits it to sound the hour, in order to warn man that time is on the wing. Two small angels perform movements also; one striking a bell with a sceptre, whilst the other turns an hour-glass at the expiration of an hour. In the last place, this work is decorated with various animals, which emitted sounds similar to their natural voices; but none of them remain, except the cock, which crows immediately before the hour strikes, first stretching out its neck and clapping its wings. Indeed it is to be regretted that a great part of this curious machine is now entirely deranged. The clock of the cathedral of Lyons is of less size than that of Strasburgh, but is not inferior to it in the variety of its movements; it has the advantage also of being in a good condition. It is the work of Lippius de Basle, and was exceedingly well repaired in the last century by an ingenious clockmaker of Lyons, named Nourisson. Like that of Strasburgh, it exhibits, on different dial-plates, the annual and diurnal progress of the sun and moon, the days of the year, their length, and the whole calendar, civil as well as ecclesiastic, The days of the week are indicated by symbols more analogous to the place where the clock is erected; the hours are announced by the crowing of a cock, three times repeated, after it has clapped its wings, and made various other movements. When the cock has done crowing, angels appear, who by striking various bells, perform the air of a hymn; the annunciation of the virgin is represented also by moving figures, and by the descent of a dove from the clouds; and after this mechanical exhibition the hour strikes. On one of the sides of the clock is seen an oval dial-plate, where the hours and minutes are indicated by means of an index, which lengthens or contracts itself, according to the length of the semidiameter of the ellipsis over which it moves. A very curious clock, the work of Martinot, a celebrated clock-maker of the seventeenth century, was formerly to be seen in the royal apartments at Versailles. Before it struck the hour, two cocks on the corner of a small edifice crowed alternately, clapping their wings; soon after, two lateral doors of the edifice opened, at which appeared two figures bearing cymbals, beat upon by a kind of guards with clubs. When these figures had retired, the centre door was thrown open, and a pedestal, supporting an equestrian statue of Louis XIV., issued from it, while a group of clouds separating, gave a passage to a figure of Fame, which came and hovered over the statue. An air was then performed by bells after which the two figures reentered, the two guards raised up their clubs, which they had lowered as if out of respect to the presence of the king, and the hour was then struck. While, however, we have thought it right to describe these ingenious performances of foreign artists, we must not neglect to mention the equally ingenious workmanship of some of our own countrymen. We now refer to two clocks made by English artists, as a present from the East India Company to the Emperor of China. These two clocks are in the form of chariots, in each of which a lady is placed in a fine attitude, leaning her right hand upon a part of the chariot, under which appears a clock of curious workmanship, little larger than a shilling, which strikes and repeats, and goes for eight days. Upon the lady's finger sits a bird, finely modelled and set with diamonds and rubies, with its wings expanded in a flying posture, and which actually flutters for a considerable time by touching a diamond button below it; the body of the bird, in which are contained the wheels that animate it as it were, is less than the 16th part of an inch. The lady holds in her left hand a golden tube, little thicker than a large pin, on the top of which is a small round box, to which is fixed a circular ornament not larger than a sixpence, set with diamonds, which goes round in or near three hours in constant regular motion. Over the lady's head is a double umbrella, supported by a small fluted pillar the size of a quill, and under the larger of which a bell is fixed, at a considerable distance from the clock, with which it seems to have no connection, 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 golden dog. In a work like the present, however we may wish to pursue this interesting subject through its progressive steps of improvement, and to do justice to the numerous scientific and ingenious men who have from time to time effected those improvements, we are compelled to confine ourselves within certain limits, which preclude us from entering more fully into detail in this article; we therefore refer such of our readers, who wish to pursue the subject, to the catalogue of writings in Dr. Young's Natural Philosophy. We shall next proceed to give a description of the mechanism of an ordinary watch, and to annex thereto a useful set of tables, published originally by Mr. W. Stirt. WATCHES. Figure 501 represents the interior works of an ordinary watch with the crown-wheel escapement, as they remain on the pillar-plate when the upper part of the frame, shown by fig. 505, is unpinned and removed; and fig. 502, which is a section of the whole frame and its contents, shows the connection of all the parts, as though the calliper were in one right line. These two figures, by having the same letters of reference, mutually explain each other. The mainspring which actuates all the wheels and pinions, that are called, in one general term, the movement, is contained in the circular box a, seen in the different views in the separate figs. 501, 502, and 508, in the last of which its parts are given in a detached state, viz. the box; the relaxed spring immediately above lying in a spiral form; the arbor with its pin, on which the interior end of the spring is hooked, and the lid through which the pivot of the arbor penetrates; this spring is forced into the box by a tool on purpose when it is strong; and then the exterior end is hooked to a pin in the circular edge of the box, so that if the box is made to turn round while the arbor is held fast, the spring begins to coil at the centre, and is thereby said to be wound up. The same effect would be produced if the box were held fast, and the arbor only were turned; but in the latter case the chain, which requires to be uncoiled from the spring-box as this spring is wound up, would remain unmoved; it is necessary therefore that the box be turned while the arbor is at rest, which is thus effected: one end of the chain is |