Fusee - Public domain portrait drawing

Woodcut of fusee and mainspring, showing operation. The fusee (cone-shaped pulley) was used in antique clocks and watches to improve accuracy by equalizing the force of the mainspring. The labeled parts are: (A) mainspring arbor, (B) mainspring barrel, (C) chain, (D) fusee axle, (E) attachment of chain to barrel, (e) attachment of chain to fusee, (F) fusee, (G) winding arbor, (W) output gear wheel. Alterations: combined two illustrations from the source, Fig. 14 p.24 and Fig.15 p.25 into one image, and added the captions.

These drawings have a slight mechanical error. The mainspring inside the barrel is depicted as wound up in the bottom drawing, with more turns wrapped around the axle, and unwound in the top drawing. However in a fusee movement the mainspring is fully wound when the chain is wrapped around the fusee, as in the top drawing, and unwinds as the chain is wrapped around the barrel. Therefore the drawings of the mainspring should be reversed, with more turns shown in the top drawing.