hourglasses

An hourglass is a device used to measure time, consisting of two glass bulbs connected by a narrow neck. Fine sand or particles flow steadily from the upper bulb to the lower one, and the time it takes for all the sand to transfer indicates a specific interval. Once empty, the hourglass can be flipped to restart the process. Its simplicity and reliability make it a classic tool for short durations, often used in games or experiments, though modern timing devices have largely replaced it for precision timekeeping.