We shall now proceed to shew how the moon's motion is produced. On the top of the month nut socket, where it lies in the plane of the dial, is cut a right handed double endless screw, working into a small brass wheel of 15 teeth, which is on the lower end of a long arbor, standing upright in a slit made in the dial. This slit is covered by a large circular silvered plate, on which are engraved the hours, minutes, and seconds ; on the upper end of this long ar bor is a pillion of 8, which carries about the wheel of 63, and with it, at the same time, the bevelled wheels, globe, and moon's age ring. The pivots of the long upright ar bor run in small cocks attached to the back of the dial. The month nut, or hour wheel socket, makes a revolution in twelve hours, carrying the hour hand. The revolution of the moon's age ring is made in 29 days, 12 hours, and 45 minutes. The wheel of 63 and 15 being multiplied to gether, the product is 945, and this divided by 8, the numb'er of the pinion, gives 118.125 times six hours, which being reduced gives the lunation, or a revolution of the moon's age ring as above, of 29 days, 12 hours, 45 minutes. The time of the revolution may be made out by another way. It is evident that one tooth of the small wheel of 15 is turn ed every six hours, of course the wheel will be made to have a revolution in 90 hours, and so will the pinion 8. Then if we say as 8 : 90 :: 63 : 708.75 hours, which is also equal to the given lunation of 29 days, 12 hours, 45 mi nutes. To produce the annual motion of the ring plate wheel of 365 teeth, the month nut is cut into 42 teeth, and makes its revolution, as was said before, in 12 hours, and turns a wheel of 84, concentric with which is a pinion of 8, leading a wheel of 96, having concentric with it a pinion of 12, leading the wheel of 365, which is the plate ring circle, having on it the days and months of the year, the degrees of the ecliptic, Exc. turning once round in 365 days. Now as 365 x 96 X 84=2943360, this product, divided by that of 42 x 8 x 12 — 4032, will give 730 times twelve hours, or 365 days. The pinion of 12 is put on a square, which comes in and through a small hole in the large silvered circular plate.; the wheel of 96 is put on a round part of the arbor, just below the pinion, and is keyed spring tight on it ; by means of a small key which fits the square, to turn the pinion, the annual wheel of 365 teeth can be set to any required day of the month, which can be done with out disturbing any of the motion-wheels. The setting of the moon's age ring is equally free as this is from any dis turbing cause. The diameter of the month nut wheel of 42 is one inch, and three and a half tenths of an inch ; that of the wheel of 84 is 2.5 inches, and near to a tenth and a half more. The wheel of 96 is three inches ; its pinion of 12 is .307 of an inch, the pinion of 8 is .316 of an inch in diameter.
The minute pipe-wheel of 56 teeth, and 1.8 inch in dia meter, runs on the arbor of the centre wheel, carrying the minute hand. It turns in the common way, the minute wheel m of the same number and diameter, whose centre lies nearly under that of the other, about .6 of an inch to the right of the middle line of the fore frame plate, and 1.7 inch from the centre of the minute hand wheel. The arbor of the minute wheel has a pinion of 8, leading in.the common way the hour wheel of 96, whose diameter is 3.25 inches, that of the pinion is .426 of an inch. This pinion of 8 is put on the arbor, by means of a square, and with th -inute wheel both are fast on the arbor. See Plate Ct CIV. Fig. 7. The upper side of the wheel may be dis tant from the lower face of the pinion about .7 of an inch, the lower side having a proper freedom of the fore plate. Two wheels, one a plain wheel of 38, the other a bevelled one of 38, having the same diameter 1.2 inch, are screwed together, and on a socket common to both ; the flat wheel is the uppermost, and is pretty close to the back of the be velled one, whose teeth look downwards ; their socket turns on the minute wheel pinion arbor, between the lower face of the pinion and the upper side of the minute wheel, having a proper end shake between them ; the back of the flat wheel of 38 is below the lower face of the pinion .4 of an inch. These wheels of 38 can be made to turn on the minute pinion arbor, independent of it and the minute wheel. The minute wheel and pinion arbor extends a lit tle way heyond and below the minute wheel, perhaps one inch and three or four tenths more to the end of its pivot ; it extends also beyond the face of the pinion more than .6 of an inch to the end of its pivot, which runs into a cock C screwed on the fore frame plate. There is a part formed
on the arbor of a flat circular shape, and whose thickness is rather more than that of the diameter of the arbor ; in the middle of this is a hole tapped, into which is screwed a stud, standing at right angles to the arbor ; a bevelled wheel of 38, and diameter 1.2 inch with its socket turns on this stud, which is placed on the arbor at that distance, so that the two bevelled wheels may fairly pitch into one ano ther ; the minute wheel is crossed into four, and through one _of the cross's openings, the bevelled wheel B, which is on the stud, gets to pitch with the bevelled wheel b which is above the minute one. On the inside of the pillar plate is screwed a cock A, near 1.2 inch in height, and so that the middle part of the upper knee shall be opposite to the lower end and pivot of the minute pinion arbor. On one end of another arbor, in length about 2.1 inches, having a shoulder on it, is rivctted a bevelled wheel c of the same diameter and number of teeth as the others ; another shoulder of just a sufficient thickness is made on this arbor at the back of the bevelled wheel ; the rest of the arbor nearly straight all the way, to the shoulder of a pivot which is at this end ; from this shoulder the arbor is squared down for about .6 or .7 of an inch, to receive the socket of a small wheel W of 32 teeth, which turns behind the pillar plate ; this wheel is nearly one inch in diameter, and a cock K is screwed on the back of the pillar plate, in which the pivot of the wheel of 32 runs; a pin is put through the socket and square, to keep the wheel fast to its place on the arbor. When the shoulder at the back of the bevelled wheel bears on the outside of the kneed cock, which is on the inside of the pillar plate, the cock having a hole in it which allows the arbor to go through and to turn in it, then the pivot of the arbor will run in the cock which is at the back of the pillar plate. The inside bottom of the bevel led wheel, which is rivetted on the shoulder of this arbor, has the end of the arbor made flush with it, and a hole made in the end and centre of the arbor to receive the lower pivot of the minute pinion, in which it runs or turns, the bevel led wheel which is on the stud being supposed to be set as low down as it shall meet and pitch properly with that which is at the end of the other arbor. It will now be seen that the end shake of these arbors, when combined, will lie between the minute pinion cock on the fore plate, and that which is on the back of the pillar plate. Let us suppose that the bevelled wheel, which is at the end of one of these ar bors, remains as it were stationary, and that the minute pi nion and wheel are carried about by the minute pipe wheel, which is on the arbor of the centre wheel ; during a revo lution of the minute wheel and pinion, the bevelled wheel, which turns on the stud, will be carried not only round with its stud, but is made to make another revolution by means of its turning round on the teeth of the bevelled wheel, which is stationary, causing the bevelled wheel, and the flat wheel connected with it, which are below the mi nute pinion, to make two revolutions in the hour ; and as the flat wheel of 38 teeth turns the sun hand wheel of 76 teeth and 2.3 inches in diameter, this last mast make its revolution in an hour. Its socket turns freely on that of the minute pipe wheel, which carries the minute hand ; between the sun hand wheel and this minute pipe wheel is a slender spiral spring, the inner end of which is fixed to the lower end of the sun's wheel socket, the outer end being fixed in a stud on the upper surface of the minute hand wheel. This spring is for the purpose of keeping forward the sun hand to its place, notwithstanding any shake which may be among the teeth of those wheels concerned in the equation motion work. The sun's hand is of bi ass gilded, having the figure of the sun on it, at a little distance from the end which points to the minute divisions. The sun's hand lies between the hour and minute hands; the wheel of 76, which carries it, besides the motion of going once round in an hour, has at one time a small motion retro grade, at another a small motion progressive, according to the equation; and there are four times in the year when the minute and sun hands are nearly together. One half near ly of the sun wheel is crossed out, on that side in which the sun's hand lies, in order that the equilibrium of the hand and wheel may be as nice as possible, whatever may be the position of the sun hand.