Marine four-hour sand-glass

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Four-hour sand-glass
Manufacturer	(unknown)
Production years	18th century
Production location	(unknown)

It has long been customary in ships to divide up the 24-hour day-and-night period into intervals of our hours, termed ‘watches’, half the ship’s company being on duty during each watch. This large sand-glass, which probably dates from the eighteenth century, is of the type which was used in ships for marking the lengths of the watches.

[edit] How it works

The glass would be hung by its ropes and inverted at the end of each watch. The four-hour period from 4 p.m. to 8 p.m. was divided into two watches, each of two hours’ duration, and the passage of every half-hour was signified by an appropriate number of strokes on the ship’s bell. An additional 30-minute sand-glass was supplied for timing these shorter intervals.

[edit] Memories

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[edit] In the Science Museum's Records

Inv. No: 1938-641