ESCAPEMENT, CROWN-WHEEL—Of the recoil type, and the earliest known escapement; to be found in Henry de Wyck's clock. Not suitable for watches. Practically the same principle as Verge or Vertical Escapement used in watches for so many years. [Illustration] ESCAPEMENT, CYLINDER OR HORIZONTAL—Invented by Thomas Tompion in 1695—later improved and brought into general use by Graham. It dispensed with the then common vertical crown-wheel—hence the term "horizontal" and permitted thinner watches. This escapement is frictional, the balance being carried on a hollow cylinder whose bore is large enough to admit the teeth of the escape wheel. The cylinder is cut away where the teeth enter and the impulse is given by the wedge shaped teeth striking against the edge of the cylinder as they enter and leave. Used at this time in the cheaper Swiss watches. [Illustration] [Illustration] ESCAPEMENT, DEAD-BEAT—Any escapement in which the pallet face is so formed that the escape wheel remains dead or motionless during the supplementary arc of the balance or swing of the pendulum. As invented by George Graham, the wheel is much the same as the wheel in the anchor escapement, the difference lying in the shape of the pallets. Each pallet has a driving face and a sliding face. It is so arranged that the impulse is given the pendulum at the midpoint of its swing thus allowing the swing to adapt itself to the impulse and keep the time constant. The pallets are faced with jewels so that there is slight friction. Used in high grade clocks such as regulators and astronomical clocks. ESCAPEMENT, DETACHED—Any escapement in which the balance or pendulum is for some time during each vibration free from the pressure of the train. Detached escapements are used in chronometers, most watches and in turret clocks. They are of value in any movement where the motive power varies greatly—hence in turret clocks. Examples: Chronometer, lever, and gravity escapements. [Illustration]