When the pendulum is set in motion, it will, by means of either One or other of the screws d, unlock the swing wheel ; which, in the drawing, is represented as being locked by one of its teeth on the nib or detent part of the right hand pallet ; and the moment 'lien the wheel is un locked, the tooth at the left hand pallet is ready to press for ward and raise up the pallet ; and, of course, it bends up the spring. Let the pendulum be now brought to the right hand side, the steel bar e will meet with the screw d, and carrying it or pushing it on, it will by this means un lock the swing wheel, and allow it to escape. At this in stant, the wheel tooth meeting with the pallet on the left hand side, it will force its way on the flanch, and raise it up till it is stopped by the detent or pallet nib. Here the wheel is locked until the return of the pendulum to that side, when it will be again unlocked. From the time of the unlocking at the right hand pallet, till the same takes place at the left hand, the pendulum, during its excursion to the right, is opposed by the spring part of the pallets, and on its return it is assisted by the same part, until the pendulum comes in contact with the point of the screw d on the left hand part : Here it is again opposed in its ex cursion, as far as the arc it describes ; and on its descent or return, it is assisted or impelled by that of the spring part of the pallet, in conjunction with the force of gravity. In this clock, all that the motive force through the wheels has to do, is to raise up the pallets, by bending up the springs ; and these, along with gravity, maintain the motion of the pendulum.
When clocks of the common construction get foul in the oil, or dirty, the arc of vibration falls off, or is less than what it was when the clock was clean and free. In this 'scapement, however, when the clock gets foul, the force of the swing wheel teeth, on the detent part of the pallets, will be lessened, consequently the wheel will more easily be unlocked by the pendulum : hence we may expect a small increase in the arc of vibration ; but whether this m ill affect the time-keeping, by making it slow, must be left to the experience of those who may think of making such trials. It appears to us, that if any lengthening or the arc of Nibration takes place, it will be equally accelerated by the greater tension of the spring part of the pallets.
Another clock, having the same kind of 'scapement, has since been made by Air Thomas Reid, where the adjust ments for 'scapement and beat are transferred from the pal lets to the pendulum itself. By this means, these adjust ments are not only easier made, but are effected without that danger to which the pallets are exposed, m hen this is done by the screws which are in them. This 'scapement has also been very advantageously applied, even where a a vet ge and crutch were adopted.
The following is a scheme and description of another clock 'scapement, which the writer of this article contrived about twelve or fifteen years ago.
In Plate CCCI. Fig. 3. SW is the swing wheel. whose diameter may be so large, as to be sufficiently free of the arbor of the wheel that runs into its pinion, which in eight day clocks is the third. The teeth of this swing wheel are cut thus deep, in order that the wheel may be as light as possible, and the strength of the teeth little more than what is necessary to resist the action or force of a common clock weight through the wheels. They are what may be called the locking teeth, as will be more readily seen from the use of them, afterwards to be explained. Those called the im pulse teeth, consist of very small tempered steel pins, in serted on the surface ()I' tue rim of the wheel on one side only. They are nearly two-tenths of an inch in height ; and the smaller they are, so much more room will be given to the thickness of the pallets. If they have strength to support about eighty or a hundred grains, they will be strong enough. There is no rule requited for placing them relatively to the locking teeth, only they may as well be opposite these teeth as am where else, P, P are the pallets,'. hose centre of motion is the same with that of the verge at a. These pallets are formed so as to have the arms sufficiently strong, and at the same time as light as may be. That part where the arms meet at the angle at a, has a steel socket made out of the same piece as the arms, being forged together in this manner. This socket is made to fit well on the verge, on which it is only twisted fast ; and is turned pretty small on the outside, in order to allow the arbors of the detents to be laid as close to the verge as may be, so that their' centres of motion may coincide as nearly as possible. A perfect coincidence of the centres might be obtained by using a hollow cylinder for the verge, with the detent arbors running in the inside of it, but this would have occasioned more trouble. That part of the
pallet frame, as it may be called, in which is set the stone for receiving the action or impulse of the small pin teeth, is formed into a rectangular shape, so as to allow room for a dovetail groove, into which the stone pallets are fixed, as may be seen at PP, Fig. 3, and at P, Fig. 4, which also gives a side view of the verge at a, and where the socket of the pallets is seen, as fixed on the verge. At b, Fig. 4, is seen the outer end of one of the stone pallets made flush with the steel. That part of the stone pallets upon which the pin teeth act may be seen in Fig. 3, where they are re presented in their respective positions relative to the pin teeth. Their shape or form is exactly that which gives the dead beat. In Fig 3. are seen the detents d, d, whose centre of motion is at c, c. They are fixed on their arbors by a thin steel socket, made as forged with the detents, much in the same way as the pallets were, as may be seen at c, Fig. 5, which gives a side view of one of the detects and its arbor. The screws e e,f, f, in the arms of the de tents, have a place made to receive them, which is more readily seen in Fig. 5. than in Fig. 3. The screws e c, serve for the purpose of adjusting that part of the 'scape ment connected with the pallets, pushing the detents out from locking the wheel, by means of the locking teeth. The ends of the screws e, e on the unlocking, are met by the ends of the stone pallets, one of which is represented at b, Fig. 4. The screws f, f, serve to adjust the locking of the wheel teeth on the detents., g are brass rectangular pieces or studs, which are filled to the inside of the pillar frame plate, and may be near an inch in height. The ends of the screwsf,f, rest on the side of these studs, and accord ing as they are more or less screwed through at the ends of the detents, so much less or more hold will the detent pieces have of the teeth. These holding pieces of the de tents are not represented in the drawing, as they would have made other parts of it rather obscure. They are made of stone, and are fitted in by means of a dovetail, cut in a piece left for that purpose, on the inside of the detent arms, as may easily be conceived from the drawing, where it is represented in part at e, Fig. 5 ; and is in the line across the arm with the screw c, which is close by the edge of the detent stone-piece, which projects a little beyond the end of the screw. Having described the parts of the 'scape ment, we shall now explain their mode of action. On the left hand side, the phi-tooth is represented as having just escaped its pallet, as seen in Fig. 3 ; but, previous to its having got on to the flanch of this pallet, let us conceive that the back of the pallet, or end piece b of it, had come, in consequence of the motioi, of the pendulum, to that side, and opposing the screw c, which is in the detent arm, pushes or carries it on with it, and consequently unlocks the tooth of the wheel, which then endeavours to get forward ; but the pin-tooth, at this instant of unlocking, meeting with the !hitch of the pallet at the lower edge inside, and pushing lb] wards on the nand', by this means impels the pendulum, and after having escaped the pallet, the next locking tooth is received by the detent on the right hand side, where the wheel is now again locked. In the mean time, while the pendulum is describing- that part of its vibration towards tne left hand free and detached, as the pallets are now at liberty to move freely and independently of the small pin teeth, on the return of the pendulum to the right hand side, the detent, by means of the back of the pallet on that side, is pushed out from locking the wheel, and, at the instant of the unlocking, the wheel gets forward, and the pin tooth is at the same instant ready to get on the flanch of its pallet, and give new impulse to the pendulum, as is obvious by what is represented in the drawing, Fig. 3 After the pin tooth has escaped the pallet, the wheel is again locked on the opposite or left hand side ; the pendulum moves on to the right freely and independently till the next locking on the left takes place, and so on. It may be observed, that the unlocking takes place when the pendulum is near the lowest point, or point of rest, and of course where its force is nearly a maximum. 'Without attaching any thing to the merits of this 'srapement, we may remark, that the clock was observed from time to time by a very good transit in strument, and, during a period of eighty-three days, it kept within the second, without any interim apparent deviation. This degree of time-keeping seemed to be as much a mat ter of accident as otherwise ; and cannot reasonably be ex pected from this, or any clock whatever, as a fixed or set tled rate.