Riefler escapement

An escapement is the mechanism in a mechanical clock that gives the pendulum precise impulses to keep it swinging, and allows the gear train to advance a set amount with each pendulum swing, moving the clock hands forward at a steady rate.

Therefore, slight variations in the friction of the pallets and in the torque from the escape wheel are passed on to the pendulum, disturbing its motion.

[7] With over 600 made,[3] they were one of the most widely used astronomical regulators, and became the highest standard for timekeeping in the early 20th century.

Riefler clocks had internal switch contacts for this purpose, which delivered a 1 Hz time signal to external equipment.

They were powered by a gravity remontoire, a small weight which was wound up by an electric motor every 30 seconds, to eliminate the effect of changes in drive force on the mechanism.

Working Riefler precision pendulum clocks on display to the public are located at the Deutsches Museum in Munich, the National Watch and Clock Museum in Columbia PA, the Musée international d'horlogerie in La Chaux-de-Fonds and the Musée d'horlogerie in Le Locle (both in Switzerland), the Deutsches Uhrenmuseum in Furtwangen, the US Naval Observatory (by appointment only) in Washington DC and in Anderson Hall at Carleton College in Northfield, MN.

Riefler escapement used in the Clemens Riefler regulator clock, 1893. Shows the bearer (A'), knife edges (c), agate support surfaces (P), suspension spring (i), locking escape wheel (h), impulse escape wheel (H), and pallets (S,S').
The Riefler precision pendulum clock No. 549, currently (2006) serving as the workshop regulator in the horological workshop of the Deutsches Museum .
Side view, closeup of double escape wheel of Riefler No.549. This clock has clear synthetic ruby pallets. (Dial on the right side.)
Riefler clock, NIST museum, Gaithersburg, Maryland, USA. 54 inches (134 cm) tall. This clock served as the first US time standard, from 1904 to 1929.