hour + glass

The hourglass is a compound of 'hour' (from Latin hora, from Greek hōra, meaning season or time of day) and 'glass' (the material of its bulbs). The device — two glass bulbs connected by a narrow neck through which sand flows — appeared in Europe in the eighth century, though the earliest definite evidence dates to the fourteenth century. The word 'hourglass' itself appeared in English in the 1500s.

Early sandglasses (as they were more accurately called) measured intervals ranging from a few minutes to four hours. Ships used half-hour sandglasses to time their watches — the ship's boy turned the glass every thirty minutes and rang a bell. Eight bells marked the end of a four-hour watch. The phrase 'the sands of time' comes directly from this device. Time was visible: you could watch it run out.

The hourglass had advantages over water clocks and early mechanical clocks: it worked in any orientation (useful on a rocking ship), required no calibration, and was portable. Its disadvantage was that it measured only one interval — you could not check the time midway. It was a timer, not a clock. The distinction matters: a clock tells you what time it is. An hourglass tells you how much time has passed.

The hourglass is now a universal symbol for waiting. Computer loading cursors used an hourglass icon for decades. The image of sand running out is the most intuitive representation of time passing — more immediate than a clock face, more visceral than a digital number. The hourglass makes time visible, physical, and finite. You can see it end.