The _Horizontal_ escapement, on the following page, so called because of the escape-wheel acting horizontally to the axis of the balance. This invention was perfected by Graham, after the death of the inventor, his master and friend, Thomas Tompion. _a_, the escape-wheel, having pins or stems rising from it, on the tops of which are teeth of a wedgelike form, of such a length as to permit little freedom within and without the cylinder _b_, which is firmly fixed to the balance _c_. Although _b_ is one piece, the two edges of the hollow part serve as distinct pallets, inasmuch as they receive alternately, during each vibration of the balance, an impulse from the curved outer edge of each tooth in succession; and as the wedge-shaped tooth passes from the pallet, the coming tooth falls on to the circular part of the cylinder, and there remains until the return of the balance, when that tooth which had previously rested on the circular portion of the cylinder, comes upon the edge or pallet, gives impulsion to the balance _c_, and falls upon the concave portion of the cylinder, and there remains until the balance again returns, when another impulse takes place, and so on in succession. Watches having the cylinder escapement were not known in France till the year 1728, when Julien le Roy obtained one of them from Graham. +----------------------------------------------------------------------+ | [Illustration: Horizontal Escapement.] | +----------------------------------------------------------------------+ +----------------------------------------------------------------------+ | [Illustration: Duplex Escapement.] | +----------------------------------------------------------------------+