The detached 'scapement of Mudge was contrived about sixty years ago or thereabouts, if we may reckon from the year 1766, when he showed it to Berthoud, who was then in London, and who informs us that it had been made a con siderable time before.
This 'scapement consists of a wheel and pallets, like those made for the dead beat 'scapement of a clock, only the wheel teeth are not cut half the depth. On the verge or arbor of the pallets is placed an arm of any lengi h, gene rally a little more than that of the pallets. (See Plate CCCIII. Fig. 5 ) The end of the arm is formed into a fork like shape. On the axis of the balance is a short pallet, whose acting end may be of a small circular form, having the sharp part of the angles blunted, coming a little way within the prongs of the fork, which alternately acts, and is acted upon. There is also on the balance axis a small roller, having a notch in it. On the end of the arm is attached a small steel piece or index, in a plane which may be either above or below the prongs of the fork ; this index is on the outside of the roller, when the free part of the vibrations is performing, and prevents the wheel teeth from getting away from the place of rest. On the return of the balance, the index passes with the notch in the roller to the opposite side. Meanwhile the short pallet gets into the foi k, meeting with one of the prongs, pushes it on a very little way, and thus disengages the teeth of the wheel from the circular part of the pallet, where they rest during the free excursions of the balance. During the disengaging, the teeth get upon the flanch of the pallet, and give impulse, which causes the opposite prong of the fork to come forward on -the short pallet, and communicate impulse to it. Iii Mudge's 'scape mem, as drawn in the plate for the work published by his son, there are two short pallets, and the prongs of the fork lie in different planes. The impulse in this 'scapement is given at every vibration ; and it seems to have done un commonly well, particularly it the watch which he made for her Majesty Queen Charlotte. It is by no means suit ed for the execution of ordinary workmen, as it requires more address than usually falls to their share. The late Emery was much taken up with it ; and although he had a little success, and had the aid of a very excellent hand, yet he experienced considerable difficulties. It might be some what easier managed, by adopting Lepaute's mode of Gra ham's dead beat, which we have tried.
In 179'2, a very neat and ingenious detached 'scapement was contrived by the late Howells, founded on that of Kendal's, (in whose hands he had occasion frequently to see it,) in which the wheel teeth rested on the cylindri cal part of the pallet, during a part of the going and re turning vibrations of the balance. See Plate CCC111. Fig.
6. In the other, after impulse is given on the face of the same semicylinder, and just before the tooth is quit ting it, a detent is presented to receive one of the wheel teeth, by which the action of the wheels is suspended during the greater part of the going and returning vibrations, the pallet being then free and independent of the wheels. This 'scapement is composed of two crown wheels on the same arbor, the points of the one being opposite to the middle of the spaces of the other. On the axis or verge of the ba lance, which stands quite close to that of the balance wheels, is a semi• cylindrical pallet, whose diameter should be ac cording to the angle of 'scapement required, which will al so regulate the distance of the wheels from each other. The pallet is put near to the collet on which the balance is rivetted ; a small arbor, having very fine pivots, is run in so as to stand parallel with that of the balance, and placed at some distance outside of the wheels, but where a line drawn from it, and passing at equal distances from the points of the wheel teeth, when continued, shall fall in with the centre of the balance; on this arbor is fixed an arm, at the end of which is a small fork and index ; on the verge or balance axis, and near the lower end, is a short pallet, and a roller connecting with the fork and index, in imita tion of Mudge's, acting in the same way as has been de scribed, but only in the locking and unlocking part. Where the arm passes between the wheel teeth, which may be at ninety degrees or so from where they act on the pallet, are fixed two detent pieces, one for each wheel, opposite to the arm, and in the same line. A part of it is prolonged be yond the arbor outside, by way of a counterpoise, where two screws in fixed studs serve here as a banking to it. It may easily be conceived, that one of the wheels being locked, suppose that on the left, the balance, when returning from the left to the right, will, by means of the short pallet and forked arm, &c. carry the detent away ; and just as the point of the tooth is free, the face of the semicylinder is presented, to meet with a tooth of the same wheel, and get impulse ; but before this tooth has nearly escaped, the de tent is ready to receive a tooth of the opposite wheel, and so on. This 'scapement gives an impulse at every vibra tion, as is clone in Mudge's. In the tenth volume of the Transactions of the Society for the Encouragement of ?rts, E.7c. there is a description and draw ing of it. It may be ob served, that were the semicylindrical pallet faced with a piece of precious stone, the 'scapement would go on for a considerable time without falling off.