Using a Sandglass

Sandglasses of different sizes and durations could measure intervals of time for ship speed and periods of duty. From Thomas Blanckley, A Naval Expositor, 1750.

Caption:
Sandglasses of different sizes and durations could measure intervals of time for ship speed and periods of duty.
Type: Illustration
Credit: Smithsonian Institution Libraries
Origin: Smithsonian Institution
Navigation Methods
 

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Sandglasses of different sizes and durations could measure intervals of time for ship speed and periods of duty.