MAINTAINING POWER OF A WATCH. 



fig. 30, where c D is the first wheel of the train from which the 

 Avatch receives its motion. The ratchet-wheel A is fixed upon 

 the base of the fusee, so as to 

 move with it. The catch, 

 m, which is pressed by a 

 spring into the teeth of this 

 ratchet-wheel, is attached to 

 the second ratchet-wheel B, 

 so that when A is carried 

 round by the chain acting 

 on the fusee, it must carry 

 the wheel B round with it 

 in the direction of the ar- 

 row/. The wheel B is con- 

 nected with the wheel c D by 

 a semicircular spring a b c, 

 which is attached to the wheel c D at c, and to the wheel B at a. 

 The catch, n, which falls into the teeth of the ratchet-wheel B, 

 is attached to a fixed point on the bed of the watch. 



While the watch is going, the wheel B, driven by the fusee, 

 draws after it the spring a be, bending it round to a certain 

 extent, and this spring acting at c, on the wheel c D, draws it 

 round in the direction of the arrow/. Now, let us suppose that 

 the watch is being wound up. The ratchet-wheel A, being 

 turned by the key in the direction of the arrow r, the catch m 

 falls from tooth to tooth, and the force it before received from the 

 ratchet-wheel A is suspended. But the spring a b c has been 

 drawn from its form of equilibrium, to a certain small extent, in 

 drawing round after it the wheel c D, as already stated, and it has 

 still a tendency to draw that wheel after it, so as to recover its 

 form of equilibrium. In doing this, it will continue to act upon 

 the wheel c D, and to carry it round while the action of the fusee 

 upon it is suspended during the process of being wound up. The 

 spring a b c is so constructed as to act thus for an interval more 

 than is necessary to wind up the watch. 



46. From what has been explained, it will be observed, that 

 timepieces in general are constructed with one or other of two 

 moving powers, a descending weight, or a mainspring, and with 

 one or other of two regulators, a pendulum or a balance-wheel. 

 These expedients are variously adopted and variously combined, 

 according to the position and circumstances in which the time- 

 piece is used, and t.he purpose to which it is appropriated. 



A descending weight as a moving power, combined with a pen- 

 dulum as a regulator, supply the best chronometrical conditions. 

 But the weight can only be used where a sufficient vertical space 

 43 



