The one which we propose to describe, is that which was contrived by Mr Reid for the clock of St Andrew's church. Suppose a small frame, separate and independent of the clock frame, to contain two wheels, one of which is the swing wheel, having within it the 'scapeenent work. The other wheel is crossed out, so as to be as light as may be, the rim being left just so broad as to admit fixing on it seven kneed pieces or teeth, each about a quarter of an inch thick and half an inch long, three of which arc on one side of the rim, and four on the other side. Three on each side have the knees of different heights, corresponding each to each. The fourth is a little higher than either of the third highest. The wheel on which these are fix ed, has a tooth prolonged beyond the rim, of the same thickness and length as the others, making eight teeth in all, having a small space left between each. These teeth become as it were so many wheels in different planes, and are at equal distances from one another, with the same ex tent of radius coming to the centre of the swing wheel ar bor, being just so much larger than that of the swing wheel, as to allow the swing wheel teeth to clear the ar bor of it. The edge or side of the teeth which rest on the swing wheel arbor is a plane, and rounded off on the oppo site side, to the point or angle formed by this plane. The arbor of the swing wheel has eight notches cut into it a little beyond the centre. These correspond to the eight teeth of the other wheel, and are sufficiently wide and deep to allow the teeth to pass freely through them. Each notch stands at an angle of 45 degrees to the one which is next it, which difference is continued along the arbor through the whole, making 360 degrees for one revolu tion of the swing wheel. On each of the arbors of these wheels was fixed a pulley having a square bottom, in which were set about ten hard tempered steel pins a little taper ed, something like the punks at the old thirty hour clocks, whose bottom was round in place of square. The pendu lum was fixed to the wall of the steeple, as well as the frame containing the 'scapement work, and the apparatus which has been described. The arbor of the eight toothed wheel had one of its pivots prolonged with a square on the end outside. The clock frame containing the movement was in the centre of the steeple, and the pinion in it, which suppose to be that of the swing wheel, had one of its pivots also prolonged and squared outside. These squared pi vots were connected by a steel rod and Hooke's joints. The main weight of the clock being put on, must urge not only he wheels to turn, but that of the wheel having the kneed teeth ; but some one or other of these teeth pressing on the arbor of the swing wheel cannot turn, consequently none of those in the large frame can turn, nor can the swing wheel turn here unless some other means are used. An endless chain was provided, and passed over the two pul lies fixed on the wheel arbors, and through two common gullies, to one of which is hung the small weight which is to turn round the swing wheel, and to the other a counter weight. The weight which turns the swing wheel, has its force placed on that side so as to make the wheel act pro perly with the pallets ; now, while the swing wheel is turning, the pendulum being supposed in its motion,) one of the other wheel teeth is gently pressing- on its arbor. Whenever this tooth meets with its own notch, it will, by means of the main weight, be made to pass quickly through it ; while passing, the small weight is wound up a little by the main one ; the succeeding tooth then meeting with the swing wheel arbor, rests on it for a quarter of a minute, till its notch comes about ; it then passes in its turn, and so on. The swing wheel makes a revolution every two minutes, in which time the wheel with the eight teeth makes also one. The minute hand, by this mechanism, when passing one of the notches, makes a start every quarter of a mi nute ; at every such passing, the small weight is wound up a little by the great or main one. After the clock had gone a considerable time with this, it was found that the kneed teeth got a little swelled on their parts of rest, by the force of the main weight which made them fall on the swing wheel arbor. To remedy this, an endless screw wheel was put on the arbor of the remontoir wheel, (or wheel with the kneed teeth,) working into an upright endless screw, on the upper end of whose arbor was fixed a pretty large fly, in order to lessen the velocity of the remontoir wheel, and make the kneed teeth fall gently on the swing wheel arbor. This helped the swelling greatly, but did not entirely prevent it, though it existed now in a de gree. The endless chain had also a tendency to wear fast ; in consequence of this, and of no provision having been made for the swelling of the kneed teeth, by making the notches on the swing wheel arbor much wider than was re quired for them when newly finished and first applied, this part of the remontoir was taken away, and the rod, with llooke's joint, was put on the square of a pivot of the swing wheel, prolonged on the outside of its frame. These matters being guarded against, it might be well for some artist in future to try such a remontoir. Dewing the four years it was in use, the clock went uncommonly well, and was the admiration of a gentleman who lived opposite the church, and who was an amateur in horology. One of mr field's men who took an interest in this clock, said it did not do so well after the remontoir was taken away. This, however, may have been more owing to a change in the po sition of the weights, than to any thing else, occasioned by a chime of eight large bells being put up in the steeple. For the weights, in place of having their natural fall, were carried a great way up in the steeple above the bells and clock, in order to fall down again ; and here a complication of rollers and pullies became requisite.
Harrison's remontoir is a very delicate spring, which is bent or wound up eight times in a minute. Were it ne cessary, a more obvious description could be given of it than that which is given with his time-keeper. In Haley's,
the remontoir spring is bent up 130 times in a minute. In the 'scapement of Mudge's marine time-keepers, what may be called the remontoir, was bent up 300 times in a minute ; the 'scapement here became in some degree whol ly the remontoir. A variety of 'scapements may be seen in Thiout, and in some of the modern periodical works.; yet, for the purpose of common or ordinary sort of clocks, they are confined chiefly to those of the dead beat, and the recoil. Where accurate performance is expected, some may have recourse to 'scapements of a different description.
About the year 1752, Le Roy, Lepaute, and other clock makers in Paris, were much engaged in making clocks having only one wheel ; and some had not even a single wheel in the movement. They were, however, more ex pensive in making, and performed much worse, than those which were constructed in the ordinary way. Simplicity in the machinery seems to have been their chief object. It requires, however, experience to know what simplicity in machinery is ; although apparently more simple, a clock having two wheels in it, will not be equal to that having three or four ; yet it does not follow, that, by having more wheels, the clock will be proportionally better : it has al ready been mentioned, that there are bounds which cannot be overstepped with impunity. This subject cannot be better exemplified than by making a comparison of one of Hindley's clocks, having two wheels, and giving thirty vi brations in a minute, with a clock giving the same number of vibrations in the same time, and with three wheels. The first or great wheel, in one of HinclIcy's, had 180 teeth, the second or swing wheel 120, and the pinion 8. The num ber of these teeth, and of the pinion leaves, amounts to 308. In the other, the wheels were 48, 40, and 30, and two pinions of 8; the sum of these is 134; the difference is 174, being the number of teeth more in the one than in the other, and more than the sum of the teeth in the three wheeled clock.
We shall now proceed to give a short account of such watch 'scapements as have been thought worthy of notice, from the old crown wheel and verge to the modern free or detached 'scapement ; but, in order that the reader may be able to follow our descriptions, we have given from Berthoud a view of an assemblage of wheels and pinions, to represent something like the movement of a watch or clock. They are contained in a frame made for the purpose of allowing them to be more readily seen. Plate CCC11. Fig. 1. DE is the pillar plate, or pillar frame plate ; G I: the fore frame plate. A is the balance ; the arbor or axis on which it is fixed is the verge, whose two pallets, p, p, scape with the teeth of the crown wheel C. The pivots of the balance turn or run in the frame; those of the crown wheel C, and of its pinion d, run in the potence 1, and in the counter potence 11, both of which arc screwed on the inside of the pillar plate, the arbor of the pinion d being at right angles to the axis of the balance. The contrate wheel K and its pinion C turn also in the frame ; the teeth of the contrate wheel pitch into the ba lance (or crown) wheel pinion, and can turn or drive it ; the third wheel L, and its pinion b, run in the frame ; the teeth of the third wheel pitch into the contrate wheel pinion, and turn it. The centre or second wheel M and its pinion a, have a long arbor going beyond the outside of the dial RS. The second wheel 'AL pitches with the third wheel pinion b, which it likewise can turn. N is the first or great wheel, pitching with the second wheel pinion a. X is the ratchet, m the click, and n its spring. On the arbor of the great wheel the ratchet is fixed ; and, on winding up the main spring, the ratchet and arbor turn freely in the hole at the centre of the great wheel, which keeps its place during the time of winding. OP is the main spring deprived of its barrel ; the inner end of it hooks on to the lower part of the great wheel arbor, and the outer end is hooked to the rim of the barrel, but is here fixed to a temporary stud. The force of the main spring, after being wound up, sets all the wheels and pinions in motion, and would oblige the ratchet and arbor to turn round independent of the great wheel ; by thin the main spring would be instant ly unbent, but is prevented from this, by the click m being forced by its spring n to fall into the teeth of the ratchet, applying its end to the face of the ratchet teeth ; by this means the main spring must unbend itself very slowly, the motion of the wheels being checked by the 'scaping of the verge with the crown wheel teeth. Q is the cannon pinion, put spring tight on the arbor of the second wheel, whose socket or cannon goes outside or beyond the dial, where it is squared for the purpose of the minute hand being put on it. T is the minute wheel, g its pinion ; the cannon pinion pitches into or leads the minute wheel ; the hour wheel N' having a hollow arbor or socket t, is put on the cannon pinion, and is led by the minute pinion which pitches into its teeth. It is on the socket of the hour wheel which comes a little above the dial, that the hour hand is put. When a wheel pitches with a pinion and turns it, the pinion is said to be driven by the wheel ; if the pinion turns the wheel, the wheel is then said to be led by the pinion. The pendulum or balance spring s s has its inner end fixed to a collet, which goes spring tight on the arbor of the balance ; the outer end is fixed or pinned to a stud fixed on the inside of the fore plate. In the action of the crown wheel teeth on the pal lets, the balance spring is either bent up or unbending; it is by the small force of it, that the balance is made to give twice the number of vibrations that it would give without it. It should have been observed, that, by putting a key on the square of the cannon pinion, and turning it about, this will not only move the minute hand about, but will oblige the hour hand to follow slowly, in the ratio of one turn to twelve of the minute hand.