[Illustration: Fig. 164]
[Illustration: Fig. 165]
In Fig. 161 we have a departure from the road ordinarily pursued. Here we see an escapement combining two levers, invented by the Chevalier de Bethune and applied by M. Thiout, master-horologist, at Paris in 1727. P P’ are the two levers or pallets separately pivoted. Upon the axis V, of the lever P, is fixed a fork which communicates the motion to the pendulum. The two levers are intimately connected by the two arms B B’, of which the former carries an adjusting screw, a well-conceived addition for regulating the opening between the pallets. The counter-weight C compels constant contact between the arms B B’. The function is always the same, the recoil and the impulsion operate upon the two pallets simultaneously. This escapement enjoyed a certain degree of success, having been employed by a number of horologists who modified it in various ways.
Some of these modifications we shall show. For the first example, then, let Fig. 162 illustrate. In this arrangement the fork is carried upon the axis of the pallet P’, which effectually does away with the counter-weight C, as shown. Somewhat more complicated, but of the same intrinsic nature, is the arrangement displayed in Fig. 163. We should not imagine that it enjoyed a very extensive application. Here the two levers are completely independent of each other; they act upon the piece B B upon the axis V of the fork. The counter-weights C C’ maintain the arms carrying the rollers D D’ in contact with the piece B B’ which thus receives the impulse from the wheel R. Two adjusting screws serve to place the escapement upon the center. By degrees these fantastic constructions were abandoned to make way for the anchor recoil escapement, which was invented, as we have said, in 1675, by G. Clement, a horologist, of London. In Fig. 164 we have the disposition of the parts as first arranged by this artist. Here the pallets are replaced by the inclines A and B of the anchor, which is pivoted at V upon an axis to which is fixed also the fork. The tooth a escapes from the incline or lever A, and the tooth b immediately rests upon the lever B; by the action of the pendulum the escape wheel suffers a recoil as in the pallet escapement, and on the return of the pendulum the tooth c gives out its impulse in the contrary direction. With this new system it became possible to increase the weight of the bob and at the same time lessen the effective motor power. The travel of the pendulum, or arc of oscillation, being reduced in a marked degree, an accuracy of rate was obtained far superior to that of the crown-wheel escapement. However, this new application of the recoil escapement was not adopted in France until 1695.