HOURGLASS

An hourglass, also known as a sandglass, is a timekeeping device that measures a fixed interval by the flow of granular material through a narrow passage between two connected glass bulbs. When upright, sand fills the upper bulb and slowly funnels through the constriction to the lower bulb. The interval is determined by the neck width, grain size and shape, and the total amount of sand, all calibrated to produce a consistent flow under dry, level conditions.

The exact origins of the hourglass are not well documented, but references to hourglasses first appear in medieval Europe in the 14th century. They were widely used for short time measurements, including church services, cooking, and maritime navigation. On ships in particular, hourglasses helped crews measure watches and coordinate duties, since they do not rely on mechanical parts that might fail in motion.

Construction commonly involves two glass bulbs joined by a narrow neck and mounted in a frame to keep the device upright. Sand—typically finely ground quartz—is preferred for its predictable flow, but other granular materials have been used historically. Humidity, tilt, and wear at the neck can affect accuracy, making precise timing difficult.

Today, hourglasses are often decorative or used for simple timing tasks such as kitchen timing, board games, or classroom demonstrations. They remain a cultural symbol of the passage of time and are sometimes used as visual countdowns in graphic design and art.