ESCAPEMENT, RACK-LEVER—Invented by Abbe Hautefeuille in 1734. Afterward made and improved by Berthoud and by Peter Litherland, who obtained a patent for it in 1794. It consisted of anchor shaped pallets on whose axis was fixed a rack, or segment of a toothed wheel which geared into a pinion on the axis of the balance. The balance was thus never free from the train and good timekeeping was made impossible. It is not now in use. [Illustration] ESCAPEMENT, LEVER-RESILIENT—Invented by F. J. Cole about 1870. A form of lever escapement designed to obviate the evils of overbanking. The points of the escape-wheel teeth are bent toward the locking faces of the pallets, the bend in the tooth acts as the banking and no pins are required. It was abandoned because expensive to make and the danger of overbanking is not considerable. ESCAPEMENT, LEVER—TABLE ROLLER—Excellent and very simple and the most common form today. It differs from the crank lever only in the action of the roller. The impulse pin instead of projecting beyond the edge of the roller is set within its circumference and raised above its plane. ESCAPEMENT, LEVER—TWO PIN—A form of Lever Escapement in which the unlocking and impulse actions were formerly divided between two small gold pins in the roller and one in the lever. Later the two roller pins were discarded, and one broad jewel pin substituted. [Illustration] ESCAPEMENT—PIN WHEEL—Invented by Lepaute about 1750. Similar in action to the dead-beat. A good and simple escapement for large clocks. The impulse is given the pendulum through the pallets by pins which stand out from the face of the escape wheel. Lepaute made these pins semi-circular and had his pallets of equal length acting on opposite sides of the wheel. Sir E. Beckett cut away part of the front of the pins which allows the pallets to act as in the diagram. The resting faces are arcs of a circle. It has been superseded by the gravity escapement for large clocks and is inferior to the dead-beat for small. [Illustration] ESCAPEMENT, RECOIL—Any escapement in which the pallets actually force the escape wheel to turn backwards a trifle with each beat of the balance. Cheap and easy to make but inferior as timekeepers to the detached or dead-beat types. ESCAPEMENT, RIGHT-ANGLED—A lever escapement so set that lines drawn between the centers of the balance, pallets, and escape wheel would form a right angle. See _Escapement, straight-line_. ESCAPEMENT, SINGLE-BEAT—An escapement such as the Duplex, or Chronometer, whose escape wheel moves only at alternate beats of the balance or pendulum. [Illustration] ESCAPEMENT, SINGLE THREE-LEGGED GRAVITY—Consists of two pallets and one three-legged locking wheel. Instead of the three pins for lifting as in the Double Three-Legged Gravity escapement there is a triangular steel block which acts against large friction rollers, pivoted one on each pallet. [Illustration]