120 



SEC. 3. MEASUREMENT. 



Fig. 1 The pallet against 



the first detent. 



Fig. 2. At the end of the pendulum 

 swing to the right. 





The action of the escapement is as follows : Suppose (as represented in 

 Fig. 1) the scape wheel to be locked and that C has been lifted from its lowest 

 position through an angle a + ft to the top of its lift. Suppose also that 

 the pendulum is moving to the right from the end of its swing at the left. 

 First, a slot or a pin in the pendulum rod (a pin is supposed here for sim- 

 plicity sake, and the path of the pin is shown by the dotted curve in each 

 Fig.) lifts G, idly, which falls back to its normal position, that of Fig. 1, 

 immediately the pin has passed ; then the rod itself, towards the end of its 

 swing to the right, impinges against a "beat" pin c in C, and, still rising, 

 carries C with it through a further angle 7. In rising through 7, C takes 

 up D, and the free end of E, which was resting on the impulse pin by which 

 it was lifted, is carried clear of that pin (now see Fig. 2), and drops on to 

 B 1 , the^ impulse pin next below, depressing F in its drop, and afterwards 

 holding F down (see E and F in same Fig.). The pendulum now returns, 

 from right to left, and C with D falls back through 7, D being arrested at the 

 fixed stop ; the free end of its arm E still resting on B 1 , and still holding F 

 down. The pendulum continuing its descent, C falls back through B (the 

 detent F being out of the way), as far as the detent G (here see Fig. 3), 

 where it stops. In this fall through /3, C gives the impulse. The pendulum 

 now moves on by itself, until presently the pin in its rod once more lifts 

 G ; not, however, idly now, but releasing C, which falling back further through 

 a to its lowest position (shown in Fig. 4), unlocks the scape wheel from 

 H. The position of II with respect to that part of C which acts upon it is 



