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.
The common epitaph:- "My Glass is run, and yours is running Mind Death for Judgement's coming." offers an explanation of the position of the hourglass. The 'run' glass placed on its side in an emblem of mortality. The upright or 'running' glass is a reminder of the remorseless passage of time and as such has a similar message to the latin phrase 'Memento Mori' - 'Remember you must die'.