Hourglass

An hourglass, also called a sandglass or sand timer, is a device for measuring the passage of time using two glass bulbs joined by a narrow neck, through which sand flows from the upper bulb to the lower one at a rate set by the neck's width and the sand's coarseness. It followed the water clock, or clepsydra, known to have existed in Babylon and Egypt as early as the sixteenth century BCE, but there is no record of the hourglass itself existing in Europe before the late Middle Ages; the earliest documented example is a depiction in Ambrogio Lorenzetti's 1338 fresco Allegory of Good Government. The earliest known record of a marine sandglass is a receipt from around 1345 for glass hourglasses bought for a ship under King Edward III of England.