French single handed oignon watch with rare escapement Circa 1690

Silver verge oignon pocket watch
–
An absolute rarity, this single handed oignon pocket watch made by Pierre Rousseau in Paris, France, circa 1690. The open faced case of this watch, which was crafted from silver, is magnificently engraved, and the white enamel dial has raised cartouches with Roman hour numerals and an iron hand. The early and extremely rare movement has a verge escapement with a pirouette.
The movement is signed.
–
Diameter: 57 mm
–
Weight: 141 g
–
Signed: Pierre Rousseau Paris
–
Oignon watches from the time of Louis XIV with a pirouette escapement are exceptionally rare. They are constructed on the principle of the very earliest watches with a balance spring. Huygens had imagined this device to increase the amplitude of the balance, which he considered too small. In operation, the verge staff carries not only the pallets, which conventionally engage the crown wheel, but also a wheel which engages a pinion on the balance staff, in effect, the arc of the balance is greatly increased and the watch appears to beat more slowly. However, the supplementary gearing for the ‘pirouette’ tends to increase the frictional losses and any intended gains are therefore likely to be cancelled out. Huygens quickly abandoned this strategy, so it is needless to say, very few examples were made.