An hourglass is a mechanical device used to measure the passage of time. It was invented about the year 250 BC and replaced the water-clock by using pure, dry sand passing through a narrow neck between two bulbs to determine the time.
It is not known for what purpose the hourglass was first devised. Some assert that the Roman army first introduced it to measure "watches" in the night.
A monk at Chartres, skilled in glass-blowing, is credited with having created the hour glass' final shape in the 8th century AD.
During the Middle Ages, the hourglass was used to time tournaments and helped housewives in boiling their eggs. Congregations were said to restrict the time of their parson's sermon by placing a sand clock conspicuously on the pulpit.
The hourglass is often depicted as a symbol that human existence is fleeting, and that the "sands of time" will run out for every human life. Artists that have recorded songs titled after the timepiece include Roger Clyne & The Peacemakers
, Lamb of God
. (Source The Encyclopedia of Trivia