Hourglass, also called sand timer hourglass, a device for measuring time. In its usual form it consists of two cone-shaped or oval glass receptacles joined by a narrow neck. Sand or a liquid (such as water or mercury) in the uppermost section of a true hourglass will run through the neck into the lower section in exactly one hour. By turning the other end up, another hour may be marked, and the process may be continued indefinitely.
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