On the arbor of the first or great wheel is fixed what may be called the fusee ratchet, working with the click and spring, which are on the auxiliary or going ratchet ; in the last is fixed a pin, which comes through the end of the auxiliary spring, and the circular notch in the great wheel, which is keyed on in the same way as in the case with a fusee ; and having also a detent and spring for the going ratchet, the whole forming the great wheel, and the me chanism for going in time of winding. On the great wheel arbor, close to the main ratchet, let a small bevelled wheel be fixed, of any small number of teeth, fully stronger than those in the great wheel, the back of the bevelled wheel lying against the main ratchet : indeed both might be made from one and the same piece of brass. Supposing the di ameter of the pillar plate to be 2.25 inches, that of the great wheel would be 1.5 inch, and the number of teeth 72 ; the bevelled teeth being half an inch in diameter, would admit 24 teeth ; and if made a little thicker than the great wheel, the teeth would be sufficiently strong. Another bevelled wheel, of the same diameter and number of teeth as the other, is fixed on a pinion arbor, (a hole being made in the potence plate, to allow the bevelled wheels to pitch toge ther,) which is placed within the frame in a horizontal di rection, in that line which passes through the centres of the great and second wheels ; one of the pivots runs in a cock, inside of the potence plate, and placed near to the great wheel arbor ; the other, which is a little beyond the pinion head, runs in a cock fixed on the outside of the potence plate. This pinion has sixteen leaves, of the same strength as the teeth of the bevelled wheels, and runs in with the edge of a toothed rack ; every revolution will be over the length of one inch on the rack, and equal to four hours, or one turn of the great wheel ; the second wheel pinion being 18. The length of rack, supposed to be 8 inches, would allow the time of going to be equal to 32 hours, 3 inches multiplied by 4 hieing equal to 32. Were the rack 12 inches long, it would admit the time of going to be 48 hours ; or the diameter of the pinion might be increased from .333 to .500 parts of an inch, and the time of going would then be somewhat more than So hours. Let a slip of wood be made 15 inches long, -iths of an inch broad, and rather more than -ith thick; on one side of this. and close to the edge, let another slip of the same dimensions, but not quite so broad, be set on edge at a right angle to the side of the other ; this will form a pattern to have two such cast in brass from it ; after being dressed up, one is left plain, the other so as to have twelve inches of teeth made on one of the edges ; the plain one is screwed to the inside of the case, arid the other is screwed on to the plain one, having the toothed edge on the right hand side of the pinion, so as to make the second wheel and pinion turn the proper way. To the ring or cap which Meioses the movement of the chronometer, are attached three pieces of brass, kneed up at each end ; the distance from the ends is about two inches and a hall; in which are holes made quite parallel to one another, and go on three steel rods, 15 inches long and .A-ths of an inch in diameter, fixed in the lower and upper ends of the case, and parallel to one another, and near to the dial of the chronometer. The case may be either of wood or brass, having a door on one side, which serves the purpose of getting at the chronometer, either to observe the time, or to push it up after it is nearly run down. In the lower part of the cap, a recess may be made to receive any additional weight requisite to load the chronometer with, in order to give greater extent of vibration to the balance ; the upper part of the case should, if necessary, be hung in gimbols, and the lower end loaded with lead to keep it steady. A chronometer might be easily fitted up in this way to go eight days, by giving more length of rack, a greater weight to the bottom of the cap, more teeth to the bevelled wheel which is on the horizontal pinion arbor, few er to that which is on the arbor of the great wheel, and the second wheel pinion to make more revolutions for one turn of the great wheel. Suppose the great wheel 80, and the second wheel pinion 16, one turn will be equal to five hours ; the bevelled wheel which is on it (being 16) will have a revolution also in five hours ; the bevelled wheel which turns it, having 24 teeth, will make a revolution in seven hours and a half. The rack being 25.6 inches long, the pinion of 16 making a revolution on it in seven hours and a half, and 25.6 x 7.5 =_-- 192, the number of hours in
eight days. The length of the case, being thirty inches, could be no inconvenience where eight days going without winding is obtained. A similar, and we think a preferable, construction might be adopted, by having the chronometer fixed, and a weight hung to the lower end of the rack, which, as in the case of a jack, would keep up the motion required for the chronometer. This plan, however, of a moveable rack would require a space for the rack to move in equal to twice its length.
On the Dividing and Cutting Engine AmoNG the inventions in the art of Horology produced in this country, may be mentioned that of the wheel-divid ing and cutting engines, which are said to have been in Vented by Dr Hooke. In the preface to the fourth edition of Derham's 4rtificial Clockmaker, he remarks, that " the invention of cutting engines, (which was Dr Hooke's,) fusee engines, and others, were never thought of till to lvards the end of King Charles the Second's reign." It is well enough known, that he contrived and used an endless screw and wheel for the purpose of dividing astronomical instruments, in 1664. The wheel-cutting engine was con trived by him in 1655; and, about the same period, he dis covered that the barometer indicated changes in the atmo sphere, and was connected with the weather. Ten years afterwards, he proposed a clock to register the rise and fall of the barometer, which was executed by Mr Coming, in a clock made for his present Majesty. Sully carried over to Paris wheel-cutting engines, which were much ad mired there, not only for their beauty, and fanciful execu tion, but also for their utility. The French artists unwil lingly admit our claim to this invention ; and could they have brought forward documents to the contrary, it would most readily have been done. They maintain, that it could trot have been invented and improved at the same time by any one man, an opinion in which we must agree with them. A wheel-cutting engine, and one which could divide almost any number, by means of an endless screw and toothed wheel, was made about 70 years ago by Hindley of York, which came afterwards into the possession of Mr Smeaton, from whom Mr Reid purchased it 30 years ago. As Hind Icy knew what had been done in this way by Dr Hooke, this seems to have been made in imitation of his, with some additions and improvements, as it is evidently nit copied from that which is described in Thiout's work, vol. i. p. 53, Plate xxiii. fig. 1. said to have been invented by M. P. Fardoil, watchmaker at Paris. Ramsden's dividing engine, for which he got a considerable premium from the Board of Longitude, was executed on this principle, the great merit of which consisted in having a more perfect screw than had hitherto been made. See our article GRADUA TION, for a copious history of Dividing Engines, and a full account of the engines invented by Rarasden and Troughton.
On Equation Clocks.
THE first equation clock, which is a very ingenious con trivance to chew both mean and apparent time, was made in London about 120 years ago. The following history of the invention is given by Berthoud in his Histoire.
44 The most ancient equation clock," says he, 44 which has come to our knowledge, is that which was placed in the cabinet of Charles II. King of Spain, and which is men tioned at the end of The 4rtificial Rule of Time, by Sully, (edition 1717,) who gives the following account of it, from an extract of a letter of the Rev. Father Kresa, of the so ciety of Jesus, written to Mr Williamson, watchmaker of the cabinet of his Imperial Majesty, of the 9th January 1715.
" What Mr Baron Leibnitz says, in his remarks at the end of Sully's book ;—that if a watch or clock did of itself make the reduction of equal time to apparent, it would be a very fine and convenient thing ;—on this subject I have to tell you, that from the years 1699 and 1700, there has been in the cabinet of King Charles II. of glorious memory, King of Spain, a clock with a royal pendulum, (a seconds' pendulum,) made to go with weights and not with springs, going four hundred clays without requiring to be once wound up. I have, by order of his Majesty, and in his presence, seen and explained the instructions, which were sent from London with watches, which contained many cu rious things. I had orders to go every clay to the palace during several months to observe the said clock, and com pare it with the sun-dial. And at that time I remarked, that it sheaved the equation of time equal and altparent, ex actly according to the Tables of Flamstead,* which dye found likewise in the Rodolphine. Tables," &c.