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