LEVER AND DETACHED ESCAPEMENTS. 



engaged in the opposite pallet. As the lever is detached from the 

 balance, except for an instant at the middle of each vibration, 

 the amount of friction is very small. Another advantage of this 

 movement is, that it is but little liable to derangement, and 

 when it is injured, is easily and cheaply repaired, while the 

 duplex and cylindrical escapements are expensive to make, and 

 can only be mended by such skilful workmen as are not often 

 found, except in the metropolis or large towns. 



43. In the class of portable timepieces used for the purposes 

 of navigation, where the greatest attainable regularity of motion 

 is required, an arrangement is adopted called the detached 

 escapement. This system is represented in fig. 27. 



Upon the arbor of the balance-wheel is attached a disc, in which 

 there is a notch i. A smaller disc, G, is also attached to it, from 

 which a small pin projects. By the oscillations of the balance- 

 wheel the notch i and the pin oscillate alternately right and left. 



A fine flexible spring, A, attached to a fixed block, B, carries upon 

 it a projecting piece, c. To the block D is attached another fine 

 spring E, which extends to the edge of the small disc G. The 

 projecting piece c, is so placed that when the spring A is not 

 raised, it encounters a tooth of the scapewheel, but when slightly 

 raised it allows the tooth to pass. The spring E rests in a small 

 fork behind the extremity of A, and presented downwards. 



Now, let us suppose the balance-wheel to swing from left to 

 right. The pin, projecting from the small disc G, coming against 

 the end of the spring E, raises it ; and this spring acting in the 

 fork behind it raises the spring A, and therefore lifts the piece c, 

 and liberates the tooth which that piece previously obstructed. 

 The scape-wheel therefore advances, but before the next tooth 

 comes to the place occupied by the former one, the balance swings 



89 



