New Detached Pendulum Escapement. 305 



advancing upon or touching any part of the pendulum, which, 

 at the instant when the pendulum requires impulse, is unlocked 

 by it so as to allow the impelling tooth to strike the pendulum 

 and communicate momentum to it; by the time when this com- 

 munication is finished the detent has returned to its place, and 

 is ready to arrest the next detaining tooth. In this way the 

 train has no communication with the pendulum except while giv- 

 ing it the impulse, and the only disturbing force which exists is 

 the resistance offered to the unlocking of the detent ; but this is 

 so feeble, and exerted through so short a distance, that it may 

 almost be overlooked. 



Nearly as the detached escapement approaches to perfection, 

 it is still liable to the serious inconvenience of communicating an 

 impulse which, because of the thickening of the oil, gradually 

 weakens, and leads to a diminution of the arc of vibration, and 

 consequently to a change in the clock's daily rate. Besides this, 

 the sudden blow which the pendulum receives excites a vibration 

 through its whole [ength, and gradually displaces, when suspend- 

 ed by a knife-edge upon a horizontal plane, the axis of motion, 

 thus rendering it necessary to place the knife-edge in the bottom of 

 a groove, and to give to it all the characters of a rubbing axis. 



The escapement which I have contrived is calculated to re- 

 move all these inconveniences, and almost to place the going of 

 the time-keeper beyond the reach of errors in the workmanship. 

 The description of the escapement will be best given by tracing 

 over the mode of its operation. 



A is the pendulum rod, represented as having nearly reached 

 the limit of its vibration to the left, and as about to touch the 

 small friction roller attached to the arm C D of the impeller 

 B C D E. The upper part of the pendulum rod is broken off 

 to shew the axis B, concentric with the axis of motion of the 

 pendulum itself, on which the impeller turns. The two axes 

 coinciding in direction, no rubbing ought to take place though 

 there were no friction roller at D ; the roller is merely placed 

 there for the purpose of preventing the bad effects of any small 

 error in the adjustment. In the drawing, the weight of the im- 

 peller is represented as sustained, through the intervention of the 

 slender spring E F, by the lifting pin F, which is placed near 

 the centre of the scapement wheel ; this wheel itself being pre- 



