The Collaborative International Dictionary
Hourglass \Hour"glass`\, n. An instrument for measuring time, especially the interval of an hour. It consists of a glass vessel having two compartments, from the uppermost of which a quantity of sand, water, or mercury occupies an hour in running through a small aperture unto the lower.
Note: A similar instrument measuring any other interval of time takes its name from the interval measured; as, a half-hour glass, a half-minute glass. A three-minute glass is sometimes called an egg-glass, from being used to time the boiling of eggs.
Usage examples of "half-hour glass".
From a shelf he took a half-hour glass, reversed it so that the bulb containing the red sand was uppermost, and stood it on the table.
Flogging the glass - turning the half-hour glass a few minutes too soon to shorten a watch on deck - was an old trick.
Lieutenants touched their hats when they realised it was their admiral amongst them, and a nervous midshipman almost turned the half-hour glass a fraction too soon, until a scowl from a master’.
It was not unknown for somebody to turn over the half-hour glass too early during each watch, so that a man’.
The quartermaster at the con cleared his throat, and as the last grain of sand fell into the lower part of the half-hour glass he cried, 'Turn the glass and strike the bell.
The sand in the half-hour glass ran out: Boston was now twenty miles away.