PLATE DLXXI.

Fig. 1. Fig. 2. Fig. 3. Fig. 4. Fig. 5. Fig. 6. Fig. 7. Fig. 8. Fig. 9. Fig. 10. Fig. 11. Fig. 12.

W. Preen Sculpt

PLATE DLXXII.

Fig. 13. Fig. 14. Fig. 15. Fig. 16. Fig. 17. Fig. 18. Fig. 19. Fig. 20. An excellent escapement of much more easy construction, is that commonly called Duplate's escapement, and with this we shall conclude our account of watch-work. Fig. 20. represents the essential parts somewhat magnified. AD is a portion of the balance-wheel, having teeth f, h, g, at the circumference. These teeth are for producing the rest of the wheel, while the balance is making excursions beyond the escapement. This is effected by an agate cylinder s p g, on the verge. This cylinder has a notch o. When the cylinder turns round in the direction o p g, the notch easily passes the tooth B which is resting on the cylinder surface; but when it returns in the direction g p o, the tooth B gets into the notch, and follows it, prefling on one side of it till the notch comes into the position o. The tooth being then in the position h, escapes from the notch, and another tooth drops on the convex surface of the cylinder at B. The balance-wheel is also furnished with a set of flat-sided pins, standing upright on its rim represented by a D. There is likewise fixed on the verge a larger cylinder GFC above the smaller one o p q, with its lower surface clear of the wheel, and having a pallet C, of sapphire, firmly indented into it, and projecting so far as to keep clear of the pins on the wheel. The position of this cylinder, with respect to the smaller one below it, is such that the tooth b being escaped from the notch, the pallet C has just past the pin a, which was at A while B rested on the small cylinder; but it moved from A to a, while B moved to b. The wheel being now at liberty, the pin a exerts its pressure on the pallet C in the most direct manner, and gives it a strong impulsion, following and accelerating it till another tooth stops on the little cylinder. The angle of escapement depends partly on the projection of the pallet, and partly on the diameter of the small cylinder, and the advance of the tooth B into the notch. Independent of the action on the small cylinder, the angle of escapement would be the whole arch of the larger cylinder between C and a. But a stops before it be clear of the pallet, and the arch of impulsion is shortened by all the space described by the pin while a tooth moves from B to b. It stops at d.

For an account of other escapements we must refer our readers to the Memoirs of the Academy of Sciences at Paris for 1748, Cumming's Elements of Clock and Watchwork, a French work entitled Machines approvées par l'Academie des Sciences, and Young's Lectures on Natural Philosophy, vol. i. p. 193, and Plate 16, vol. ii. p. 193.