The success of the clock depended on the invention of a device which could control the release of power from its source. Around the later part of the 13th century, the verge escapement was invented and during the next three centuries, this escapement was greatly improved upon. The problem, though, was that the verge escapement was not an accurate timekeeper.
By the late 16th century, European astronomy had advanced to the point where more accurate timekeeping was required. That is when Jost Bürgi, an inventor, astronomer, mathematician, and clockmaker; invented the cross-beat escapement (1584-1590).
The cross-beat escapement improved upon the verge escapement by adding two foliots instead of one, geared to each other, which helped to significantly improve the accuracy of the mechanical clock, and allowed Bürgi’s clocks to be accurate within one minute per day. These clocks were important because they could satisfy the exacting requirements of the astronomers of the period.
The cross-beat escapement was eventually followed by more advanced escapement technologies: anchor, deadbeat, detent, cylinder, duplex, lever, grasshopper, gravity and co-axial escapements. And, while the cross-beat escapement may be an easily forgotten piece of watchmaking history, it is still one of significant chronometric importance.
Fortunately, there are still some outstanding examples of Bürgi’s cross-beat clocks which have survived. Examples can be seen at the Staatliches Landesmuseum in Kassel, the Staatlicher Mathematisch-Physikalischer Salon in Dresden (clock from Dresden shown above) and the Kunsthistorisches Museum in Vienna.