The verge escapement, called also the crown-wheel escapement, is by far the simplest and presents the least difficulty in construction. We regret that the world does not know either the name of its originator nor the date at which the invention made its first appearance, but it seems to have followed very closely upon the birth of mechanical horology.
Up to 1750 it was employed to the exclusion of almost all the others. In 1850 a very large part of the ordinary commercial watches were still fitted with the verge escapement, and it is still used under the form of recoil anchor in clocks, eighty years after the invention of the cylinder escapement, or in 1802. Ferdinand Berthoud, in his “History of the Measurement of Time,” says of the balance-wheel escapement: “Since the epoch of its invention an infinite variety of escapements have been constructed, but the one which is employed in ordinary watches for every-day use is still the best.” In referring to our illustrations, we beg first to call attention to the plates marked Figs. 145 and 146. This plate gives us two views of a verge escapement; that is, a balance wheel and a verge formed by its two opposite pallets. The views are intentionally presented in this manner to show that the verge V may be disposed either horizontally, as in Fig. 146, or vertically, as in Fig. 145.
[Illustration: Figs. 145 and 146]
[Illustration: Fig. 147]
Let us imagine that our drawing is in motion, then will the tooth d, of the crown wheel R, be pushing against the pallet P, and just upon the point of slipping by or escaping, while the opposite tooth e is just about to impinge upon the advancing pallet P’. This it does, and will at first, through the impulse received from the tooth d be forced back by the momentum of the pallet, that is, suffer a recoil; but on the return journey of the pallet P’, the tooth e will then add its impulse to the receding pallet. The tooth e having thus accomplished its mission, will now slip by and the tooth c will come in lock with the pallet P and, after the manner just described for e, continue the escapement. Usually these escape wheels are provided with teeth to the number of 11, 13 or 15, and always uneven. A great advantage possessed by this form of escapement is that it does not require any oil, and it may be made to work even under very inferior construction.
[Illustration: Fig. 148]