Louis Leroy and Co Paris Precision master clock Bronze, brass, steel, invar, glass. Height: 145 cm. Diameter: 31 cm. Dial signed: L. Leroy & Cie 7 Bd de la Madeleine A Paris Circa 1925 This clock is housed in a metal cylinder hermetically sealed by a glass dome. Designed to operate under constant pressure, it was the master clock at the Neuchâtel Observatory from 1925 to 1957. In addition to a barometer and thermometer, the electric movement, which only indicates seconds, has a Reid escapement and an invar-rod pendulum. The amplitude of the pendulum, marked on a graduated sector on its rod, can be read through a microscope. To lessen the effect of variations in atmospheric pressure on the pendulum, some precision clock manufacturers, one of whom was S. Riefler of Munich, began, at the end of the 19th century, to put movements inside hermetic domes, where pressure could be reduced by pumping out the air. History: 1960 (donated by the Neuchâtel Observatory). Bibliography : MIH, 1974, p. 131, illus. Erbrich, 1978, p. 197, illus.