Volume 183001

Mechanics / By Henry Kater and Dionysius Lardner.

  • Henry Kater
Date:
1830
Catalogue details

Licence: Public Domain Mark

Credit: Mechanics / By Henry Kater and Dionysius Lardner. Source: Wellcome Collection.

    227/408 page 195
    In stationary clocks, and in other cases in which the bulk of the machine is not an objection, a descending weight is used as the moving power. But in watches and portable chronometers, this would be attended with evident inconvenience. In such cases, a spiral spring, called the mainspring, is the moving power. The man- ner in which this spring communicates rotation to an axis, and the ingenious method of equalising the effect of its variable elasticity by giving to it a leverage, which increases as the elastic force diminishes, has been already explained. (255.) A similar objection lies against the use of a pendulum in portable chronometers. 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 representedinfig.111.bis. A is the balance wheel bearing pallets pp upon its axis; Cis 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 crown wheel K. On the axis of this is placed the pinion e, which plays in the teeth of the third wheel L. The pinion 6 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 0 2
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