About two or three years or so after the publication of this tract, Mr Corning contrived a clock 'scapement, near ly on the same principle as that of Mudge's, where the mo tion of the pendulum was maintained by the force of gra vity of two small balls, which acted upon it during the time of the descent. In this 'scapement, the centre of motion of the pallets is independent of that of the pendulum and verge, although the same, and concentric with them ; two detents were applied for locking the swing wheel teeth, one for each pallet ; from each of the pallet arbors a wire projected in an horizontal position, and on the end of these wires the balls were fixed, which were alternately raised up, at every vibration of the pendulum, by means of the action of the swing wheel teeth on the pallets. In a peri odical philosophical journal, it_is insinuated that Mudge had borrowed the idea of the 'scapement, which he used in his time-keepers, from this of Cuming's. That Mudge's 'scapement was his own invention, is clearly evident from the hisorical facts which have been stated. And although there is an apparent similarity between Cuming's and it, yet we are not inclined to be of opinion, that Mr Curving borrowed his from Mudge's. The 'scapement of the clock made by Coming lb, his Majesty the king in the year 1763, is of the free or detached kind, a name which was not then known. The improvement which he himself made up on it two or three years after, was to keep up the motion of the pendulum by the gravity of two small balls, indepen dent of the motive force through the wheels of the move ment. In this 'scapement, he insists on the adjustment between the pendulum screws and crutch being made so as just to unlock the swing wheel and no more. This can then he only unlocked at the time, \Olen the force of the pendulum in its ascent is nearly gone, and that the pendulum should not then meet with the arm of the ball, but to receive it, as it were, just before the descent of the pendulum has commenced. In that part of Mr Mudge's, each pallet and detent were formed in one, and the un locking takes place a considerable while before the end of the vibration. Thus, the springs which maintain the mo tion of the balance are bent up, not only by means of the action of the swing or balance wheel teeth on the pallets at every vibration till the wheel teeth are locked, but are • still a little more bent up when unlocking by the exertion or momentum of the balance, or pendulum itself, previous to the vibrations being nearly finished ; and this is one of the greatest properties of this 'scapement, whether it is applied to the balance and spring, or to the pendulum. No 'scapement appears to be better calculated than this is, to keep the pendulum or balance constantly up to the same arc of vibration, notwithstanding its having what some have been pleased to call a defect in the recoiling one, that of opposing the balance or pendulum in its as cent, and promoting its descent. In the spring pallet 'scapement, as in the recoiling one, the pendulum is op. posed in its ascent, and has its descent equally promoted ; but there is still a difference between them, notwith standing this similarity. In the spring pallet 'scapement, DO retrograde motion is given to the wheels, pinions, and pivots, which produces that early wearing on them, and where the seconds' hand partakes also of this retrograde motion, as in the common recoiling 'scapement. These are circumstances which have no place in that of the other. In such 'scapements as those now mentioned of ikludge's or Cuming's, it has been said by some, that it matters not what sort of work the clock movement is, or however ill it may be executed; since the motion of the pendulum is kept up by a force, which, in some degree, is independent of the motive force produced through the wheels in the movement. This may be so far true, yet there is no 'scape ment, where any irregularity in the pitchings, pinions, &c. of the movement will be more readily discovered than in this, during the going of the clock, which will be very perceptible to the ear at the time of raising up the balls, or that of bending up the springs. We would therefore by no means advise, that this sort of 'scapement should be put to a movement of indifferent execution : on the contrary, it seems to require one finished in the best possible manner. The motive force put to it requires to be greater than that which is usually put to clocks having the dead beat 'scape ment. It may be asked, whether weights or springs are the best for these sorts of 'scapements, which is perhaps a question not easy to be resolved. We confess that springs appear to be preferable ; they seem to have, as it were, an alertness or quickness of action, when compared to the apparent heavy dull motion of gravity in the balls. The pivots which arc at the centre of motion of the pallets and balls would be regarded by many as objectionable, from the belief that oil is necessary to them. Oil does not seem to us in the least degree requisite, considering the very small angle of motion which they would have ; and we have always thought, for the same reason, that oil was not necessary to the pivots of such dctents as were sometimes used in the detached 'scapement.
We shall now proceed to give a description of a clock 'scapement, on the same principle as that of Mudge's in his marine time-keepers, which was put to a very capital regulator or astronomical clock, made some years ago by Mr Thomas Reid, for Lord Gray's observatory at Kinfauns Castle. It had a mercurial compensation pendulum, and its time of going without winding up was linty-five days. The great wheel, the second wheel, and the swing wheel pivots, were run on rollers, three being put to each pivot. Rollers were first applied by Sully to the balance pivot of his marine time-keeper, and have since been adopted by Berthoud, Mudge, and others. They have sometimes been used for clock pivots, but in such an injudicious man ner, that, in place of relieving the friction of the pivots, they have at last jainbed them to such a degree, that the pivot could not at all turn or revolve upon them.
In Plate CCCI. Fig. 1. SW is the 'scapement or swing wheel, whose teeth are cut not unlike those of the wheel for a dead beat, but not near so deep. P, P are the pal lets, the upper ends of whose arms at s, s are made very thin, so as to form a sort of springs, which must be made very delicate ; for, if they are any way stiff, the force of the swing wheel will not be able to bend them when rais ing up the pallets. In order that these springs may have
a sufficiency of strength, and at the same time be as delicate as possible, they are cut open at the bending parts, as may be seen at Fig. 2. These springs come from a kneed sort of sole, formed from the same piece of steel, by which sole they are screwed on to cocks, which are at tached to the back or pillar plate of the clock-frame. The pallet arms must be made very light and stiff, in order that their weight may have the least possible load or burden on the springs; a, a are the arms of the pallets, as repre sented in the front view, Fig. 1. and are fully as broad as is necessary. Their thickness may be made much less than this. An edge view of the pallet arms is seen in Fig. 2. The acting parts of the pallets at P, P, Fig. 1. should be made of such thickness as to allow room for inserting a piece of ruby, agate, or any fine or hard sort of stone, the thickness of the stone being a very little more than that of the 'scapement or swing wheel. Each of these stone pallets has a sort of nib or detent for the wheel teeth, which is left at the end of the pallet flanches, as may easi ly be seen at the left hand pallet, Fig. 1. These nibs are made for the locking of the swing wheel teeth, and their use will be more particularly explained afterwards. On the back of the pallets are screwed to each a kneed light brass piece, c, c, as seen at Fig. 1. On the lower ends of these kneed pieces, the screws d, d are put through, serv ing the double purpose of adjusting the 'scapement, and setting the pendulum on beat. The upper part of the pendulum-rod is composed of a sort of frame, whose steel plates A. A, A, A, Fig. I. are represented as being con tained within the dotted circular lines; the thickness of these ring-sort of plates is seen at A, A, A, A, Fig. 2. This frame has three pillars to keep the plates properly together ; and though they are not represented in the drawing, yet any one may readily conceive where their places ought to be, and what should be their length and height. At e, e, Fig 1. is seen on each side the ends of a thin steel plate, or traverse bar, which goes from plate to plate, and is fixed in the frame. An oblique view of one of them is seen at e, e, Fig. 2. In the steel frame plates, there is a circular opening, as represented by the dotted inner circle, Fig. 1. This opening must be of such a diameter as to allow the swing wheel and the cock which supports it to come freely through ; a part of the cock is seen atf,f, Fig. 2. the sole of which F is screwed to the back of the pillar plate of the clock ; the other knee K turns up to receive the pivot of the arbor of the swing wheel, the pivot at the other end of this arbor being sup posed to run in the fore plate, or in a cock attached to it, and it is the pivot which carries the seconds' hand. This description of the manner by which the so ing- wheel is sup ported within the pendulum, it is to be hoped will be suf ficiently understood, hotwithstanding the want of a proper drawing of that part. The swing-wheel S W, and part of its pinion arbor g, are seen edgewise at Fig. 2.; also the arm a of one of the pallets P, and its screw d bearing on the steel bar e, e. At the point of contact between the end of the screw d and the bar e, a small piece of fine stone may be inserted into each bar. This will prevent any wearing or magnetic attraction which might otherwise take place, if the screw was left solely to act on the steel bar ; for the smallest wearing here would in some degree alter the effects of the 'scapement. In Fig. 1. B represents a part of the bar of the pendulum rod, which is fixed into the lower part of the steel frame ; an edge view of this bar is seen at B, Fig. 2. At the upper part of the steel frame is inserted a piece c, c, Fig. 1. and 2.; in this piece the pendulum spring is fixed, whose top-piece goes into a strong brass cock, which is firmly attached to the back of the clock-case, or to a large stone pier; the end of the pro jecting part of this cock is seen at Dll, Fig. 1. and a side view of this part of it at DD, Fig. 2. The top piece of the pendulum spring has a long and strong steel pin through it, which lies in a notch made across on the up per side and projecting part or the pendulum cock. By this strong pin, the pendulum is suspended. In the side of the pendulum-spring top-piece, is made a large hole, so as to admit freely a strong screw, the head of which is seen at E, Fig. 2. This screw serves to pinch the top-piece and cock firmly together, after the pendulum has been made to take a true vertical position. This strung pin and screw are not lepresented in the drawing, but the descrip tion which has been given will, it is presumed, easily sup ply this want. In the pendulum spring- le, h, Figs. 1. and 2. may be seen an opening in it, so as to have the appearance of a double sluing, as seen at h, h, Fig. 2. This opening is made to allow the spring parts of the pallets a, a to be brought very near together, and this at the bending part of the pendulum spring, so that it and the bending part of the pallet springs should be as it were in one common centre. A part only of the cocks on which the spring pallets are screwed, is represented by k, k, Fig. 1.: ni, in are the heads of the screws by which they are fixed to these cocks. It must be observed here, that the spring pallets arc so placed, that they should act on the line of suspension and gravitation of the pendulum, which necessarily brings the swing wheel to the place where it is ; no verge, crutch, or fork, are required ; the influence of the oil on the verge pivots, and the friction by the crutch or fork on the pen dulum rod, are clone away by this arrangement. The mo tion of the pendulum is kept up entirely by the force of the spring part of the pallets, independent of any impedi ment in the wheel work, so long us it has force sufficient to raise up the pallets readily and easily : this force may be considered as permanent and invariable, and so should be the arc described by the pendulum. If the length of the pendulum and of the arc it describes arc invariable, so should be the time which is kept by the clock. lInving, described the parts which compose this it will now be requisite to show their mode of action, which is extremely simple.