The _Duplex_ escapement is of a very peculiar construction, and nearly approaches the chronometer; it is probable that it was originally invented by Dr Hooke, although, as we now have it, it came from the hands of Tyrer. It is seen in our illustration. A, the escape-wheel; B, the escape-wheel teeth; C, the balance; D, the pallet of impulse; E, the ruby roller; F, a notch in ditto: 1, 2, 3, cogs or upright teeth on the rim of the escape-wheel. The balance is supposed to be turning downwards towards the right, the tooth of the escape-wheel just resting against the ruby roller. When this (which is called the return) vibration is complete, the balance, by the strength of the hair spring, is carried in the opposite direction, and as the notch F passes the tooth of the escape-wheel, this latter is enabled to pass the roller, and the upright tooth or cog falls upon the pallet D, and thus gives impulse to the balance. The next straight tooth of the escape-wheel is now resting against the roller _e_, and the same operation again takes place. This escapement is much superior to the horizontal, and is almost independent of oil. It can carry a balance of much greater weight, and when well made performs admirably. Duplex watches, however, should never be selected by persons who are accustomed to ride on horseback, as these instruments are liable to be affected by any sudden motion. Even the stepping quickly from a vehicle may stop them, and yet the escapement be as perfect as possible. They are only adapted for persons of very quiet habits. Thomas Mudge, in the year 1766, introduced an admirable invention, which, after many alterations and improvements, is now universally known as the '_Patent Detached Lever_' escapement, represented by--_a a_ the escapement-wheel, _b b_ the ruby pallets, _c_ the lever, _d_ the balance. On the axis of the balance _d_, towards the lever _c_, is a small disc of steel, into which is inserted a small pin made of ruby. This pin fits with great nicety into a notch or opening in the end of the lever _c_, upon which are firmly fixed the two pallets _b b_, into which are secured rubies very finely polished. The balance in its vibration on either side, carrying with it the steel disc and ruby pin, causes that pin to enter the notch in the lever and carry the lever with it, and at the same time, to draw the pallet from the tooth of the escapement-wheel _a_. Power being exerted upon this wheel by the mainspring, the wheel tooth gets disengaged from the locking-face of the pallet, forces itself down the slopes of the pallet, and thus gives impulse to the balance. At each vibration the same unlocking takes place, but as soon as the wheel tooth falls from the slope, the opposite pallet is prepared to receive the advancing tooth of the escapement-wheel, and so on in succession beat after beat takes place. So excellent was this escapement considered a few years back, that chronometers were made upon the principle, and placed in the Royal