THE LEVER AND WHEEL WORK. 



267 



ing power. The manner in which this spring communicates rotation to an 

 axis, and the ingenious method of equalizing the effect of its, variable elasticity 

 by giving to it a leverage, which increases as the elastic force diminishes, has 

 been already explained. 



A similar objection lies against the use of a pendulum in portable chronom- 

 eters. A spiral spring of a similar kind, but infinitely more delicate, called a 

 hair-spring, is substituted in its place. This spring is connected with a nicely- 

 balanced wheel, called the balance-wheel, which plays in pivots. When this 

 wheel is turned to a certain extent in one direction, the hair-spring is coiled 

 up, and its elasticity causes the wheel to recoil, and return to a position in 

 which the energy of the spring acts in the opposite direction. The balance 

 wheel then returns, and continually vibrates in the same manner. The axis 

 of this wheel is furnished with pallets similar to those of the pendulum, which 

 are alternately engaged with the teeth of a crown wheel, which takes the place 

 of the 'scapement wheel already described. 



A general view of the work of a common watch is represented in fig. 34. 



Fig. 34. 



A is the balance wheel, bearing pallets p p upon its axis ; C is the crown 

 wheel, whose teeth are suffered to escape alternately by those pallets in the 

 manner already described in the 'scapement of a clock. On the axis of the 

 crown wheel is placed a pinion, d, which drives another crowft wheel, K. On 

 the axis of this is placed the pinion c, which plays in the teeth of the third 

 wheel L. The pinion b, on the axis of L, is engaged with the wheel M, 

 called the centre wheel. The axle of this wheel is carried up through the 

 centre of the dial. A pinion, a, is placed upon it, which works in the great 

 wheel N. On this wheel the main-spring immediately acts. O P is the 

 main-spring stripped of its barrel. The axis of the wheel M, passing through 

 the centre of the dial, is squared at the end to receive the minute-hand. A 

 second pinion, Q, is placed upon this axle, which drives a wheel, T. On the 

 axle of this wheel a pinion, g, is placed, which drives the hour-wheel V. This 

 wheel is placed upon a tubular axis, which encloses within it the axis of the 

 wheel M. This tubular axis, passing through the centre of the dial, carries 

 the hour-hand. 



The wheels A, B, C, D, E, fig. 32, correspond to the wheels C, K, L, M, 

 N, fig. 34 ; and the pinions a, b, c, d, e, fig. 32, correspond to the pinions d, c, 

 b, a, fig. 34. From what has already been explained of these wheels, it will 

 be obvious that the wheel M, fig. 34, revolves once in an hour, causing the 

 minute-hand to move round the dial once in that time. This wheel at the 

 same time turns the pinion Q, which leads the wheel T. This wheel again 



