Chap. XI.

MECHANICS.

983

Fig. 1437.

Fig. 1138

Recoil Escapement , invented in 1680 by Clement of London .

The escapement wheel 66 receives from the mover a circularcontinuous motion, which makes the sides of the teeth perpendi-cular to the sides of the wheel advance, and transmits this mo-tion to the lever or pallets carried by the vertical axle A, to whichthe balance wheel is fixed. The alternate motion or vibration of thebalance wheel is here produced by the action of the wheel bb on thepallets of the axle of the balance-wheel; they form together an angle ofabout 90 degrees, in such a manner that when one tooth of thewheel has escaped the pallet k , the other pallet presents itself to a toothdiametrically opposite, which in its turn escapes, so that the wheelalways turning in the same direction gives vibrations which regu-late and moderate the velocity of the wheel 66, and consequently of the system.

Dead-beat Escapement for Seconds Clocks , invented by Graham. Thepiece which forms the escapement is like an anchor, but with thisdifference, that the pallets of the anchor are so constructed, thatthey do not cause any recoil, and in consequence this escapementis a dead beat, by means of portions of circles formed on the pallets,corresponding with the inclined planes which produce the impulse oraction which maintains the motion of the pendulum.

Graham’s dead-beat escapement, employed in pendulum clocks, beingexecuted with required care and precision, is one of the most perfectwhich can be used in these machines, especially by making the palletsof rubies, as some have done.

The following is the manner in which the escapement acts: suppose the part a justescaped, 6 receives the shock of the ratchet tooth ; the vibration being finished, thepallet buries itself in the tooth without touching it, the vibration returning; the ratchetwheel remains immovable, and only acts when the inclined plane presents itself to the pointof the tooth: for this purpose the tooth acting on the plane obliges the pallet to escape,and in escaping the tooth c falls ; it strikes the circular part of the pallet a, and is retaineduntil its inclined plane presents itself; the tooth of the ratchet then ceases to be immov-able, but follows the inclined plane of the pallet, and in escaping restores motion to thependulum.

Cylindrical dead-beat Escapement for JVatches , invented by Gra •ham. a is an escapement-wheel furnished with an inclined plane 6;these inclined planes should be raised on the plane of the wheel; thebalance-wheel is carried by a cylindrical axis, one part of which ishollowed, as at c; the inner diameter of this hollow cylinder is equalto the length of a tooth, and can turn nearly one revolution roundit: it will be seen by this description, that the balance-wheel comingfrom a towards c, remains in repose ; and when the point a arrivesat the extremity of the inclined plane 6, the latter transmits the actionof the wheel to the balance-wheel, and leans against the inner partc of the cylinder: the wheel still remains in repose; the balance-wheel returns in an opposite direction, again receives the action of the same inclined planeon its leaving c, and the following tooth leans on its outer part in the same manner as thepreceding, and so in succession.

Dead-beat Escapement with Pins , by Ament , Clochmaker atParis . This is composed of a plain wheel in which a row ofpins is fixed; the pin quitting the pallet a, that of 6 receives theshock of the escapement: the vibration continuing, the pallet 6remains still, and the wheel rests immovable, which causes thesecond hand not to recoil; the vibration returning, the pinacting on the inclined plane restores the motion.

Escapement with free Vibrations , Arnold's Principle, c is theescapement-wheel, d a cut piece fixed to the axle of the balance-wheel, t a small salient point fixed also to the same axle, n aspring whose centre of motion is at r; this spring tends con-stantly to approach the wheel c, and stops its motion bythe salient part m .• at its extremity a point p rises ; the springnm is furnished with another, extremely delicate, s, whose centreof rotation is at r.

Supposing the balance-wheel turning the point of its axlewill meet the extremity of the spring s> and will pass beyond,only experiencing a very feeble resistance; but on the contraryoscillation, the spring will meet the obstacle p, which is at a ^ ^

its extremity, and instead of bending at r, it obliges the spring nm to turn round n, and

3 r 4

Fig. 1439.

Fig. 1440.

n

■Z)

Fig.1441.very slight distance from