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David

Darling

hourglass

hourglass

17th century hourglass in the Istituto e Museo di Storia della Scienza, Florence.


A hourglass is an ancient instrument to measure the passage of time. A quantity of fine, dry sand is contained in a bulb constricted at its center to a narrow neck. The device is turned so that all the sand is in the upper chamber: the time taken for the sand to trickle into the lower chamber depends on the amount of sand and on the diameter of the neck.