LE ROY, PIERRE—1717-1785. Son of Julien Le Roy. Esteemed the greatest of all French horologists. He invented a form of duplex escapement and an escapement which formed the basis for the present chronometer escapement. LEVER—That part of a lever escapement to which are attached the pallet arms, and which thus transmits motion from the escape wheel to the balance. LIFT, OR LIFTING ARC—That portion of the oscillation of a balance during which it received its impulse. The remainder of the turn is called the supplementary arc. LIGHTFOOT, PETER—A Glastonbury monk, maker of the Glastonbury and Wimburne clocks, 1335. LIPS—In a cylinder escapement, the rounded edges of the cylinder through which the escape wheel gives impulse to the balance. LOCKING—1. The stopping of the escape wheel of a watch or clock. 2. The portion of the pallet on which the teeth of the escape wheel drop. 3. The depth to which the escape tooth laps upon the pallet at the moment it leaves the impulse face. LOGAN, JOHN—Born in Lowell, Mass., 1844. Invented a new method of tempering springs and made superior main and balance springs. He was connected for several years with the Waltham Watch Company, during which time he invented many labor-saving machines. Died 1893. LONGITUDE—The circular distance east or west subtending the angle which two meridional planes make at the axis of the earth, one of them being a standard reference meridian. LONGINES—A watch factory at St. Imier in the Jura Mountains, near La Chaux de Fonds, established in 1874. Here all parts are made under one roof and the work is done by machinery. LOWER PLATE—The plate in a watch nearest the dial. Also called the "dial plate." It carries the lower pivots of the movement. LUITPRAND—A monk of Chartres who revived the art of glass-blowing at the end of the 8th century. To him is sometimes ascribed the invention of the sand-glass. LUMINOUS DIAL—A watch dial whose hands and figures are so treated as to be visible in the dark. Formerly accomplished by a phosphorescent paint which required frequent exposure to sunlight to be effective and retained its luminosity only an hour or two. Now effected by means of a compound absolutely independent of the sunlight and of a lasting glow. See _Radiolite_. [Illustration] LUNETTE—The usual form of rounded watch crystal. MAINSPRING—The long steel ribbon used for driving a clock or watch. The spring is coiled into a circular metal box called the barrel and the outer end of the spring is fastened to the barrel; the inner end to the arbor of the great wheel. First applied, replacing weights, by Peter Henlein of Nuremberg, about 1500. MAINTAINING POWER—The device for driving the train while a watch or clock is being wound.