The iconic timekeeping piece commonly known as an hourglass, often viewed as a symbol of death and the march of time, has been around since the late Middle Ages. Hourglass aliases include “sand clock,” “sand glass” and “time glass,” as well as “the poor man’s clock,” a reference to its affordability.
The earliest hourglasses employed glass spheres that were blown separately and connected by a doughnut-shaped seal of cording and wax. Technological improvements made later hourglasses more efficient. After 1760, the spheres were blown in one piece, eliminating the seal that often failed.
In March 1764 Peleg Thurston and Sons advertised hourglasses in the Newport (R.I.) Gazette, offering many sizes including “quarter and half-minute glasses; half-hour; one and two hour-glasses.” Made in England sometime between 1765 and 1800, this example is crafted from oak and glass. Though river sand likely fills this hourglass, powdered marble, silver powder, tin powder, ground cinnamon and powdered egg shells could also be used.
Hourglasses were commonly used on ships to determine time at sea, distance between ports in conjunction with the speed of a ship, and the calibration of watches. The granular material inside the glass spheres generally remained unaffected by moisture and the constant swaying of the ship, unlike other timekeeping devices. Clergy and scholars also used them to regulate sermons, meditations and study routines.