Cross-beat escapement

Jost Bürgi is credited with inventing the cross beat escapement in 1584. The cross-beat escapement is a variation of the verge escapement but with two coupled foliot elements that rotated in opposite directions. The foliot is the oscillating horizontal bar that carries a weight at each end. By all accounts his clocks incorporating this technology improved on other clocks of the time by an order of magnitude, improving the accuracy to within a minute a day, but this improvement was likely due to a number of factors associated with the quality of workmanship rather than the escapement itself.

Jost Bürgi is also credited for developing the gravity remontoire around 1595 which allowed further improvement in accuracy. The “Kalenderuhr” (three month running, springdriven, calendar-desk-clock) Burgi made for William IV, Landgrave of Hesse-Kassel (or Hesse-Cassel) (now Inventory No. U 47 at the Naturwissenschaftlich-Technische Sammlung in Kassel) is widely considered the oldest surviving clock with a remontoire, even if it does not provide power to the escapement during the few seconds of the daily cycle where the remontoire weight gets wound up by the spring. Today remontoire mechanisms are all designed to deliver power to the escapement during the remontoire reset cycle.

Learn more:

Jost Bürgi the clockmaker

Cross-beat escapement

Ken Kuo – Animated video of the cross beat escapement

Biographical Dictionary of the History of Technology

Remontoire