Marine timekeeper with constant force escapement by Josiah Emery

Marine timekeeper No. 1 by Josiah Emery, London, 1792. Keyhole-shaped brass upright case with screwed on back. Engraved 'No. 1' on the front under the dial and on the back. Also with a wood and padded leather, baize-lined, protective box. White enamel dial with three subsidiary dials and gold hands for hours, minutes and seconds. Fusee movement with constant-force escapement, and bi-metallic balance running in four anti-friction rollers with diamond endstones. Signed on the movement 'Josiah Emery Charing Cross London No. 1'.

Presented to the museum of the Worshipful Company of Clockmakers by Percy Webster in 1923. Clockmakers' Museum No. 602.

This is the surviving one of four similar machines made by Emery and submitted for trial at Greenwich in 1792, where it produced disappointing results, due to imperfections in its balance.