Hourglass first appears Exactly when the hourglass (or sand clock) was invented is unclear. It seems likely that the Greeks and Egyptians knew of this type of timekeeper; however, the hourglass as we recognise it does not appear in the historical record until the 1300s, when it shows up on the inventories of sea vessels, in the frescos of Ambrogio Lorenzetti, and in written records as well. Further Reading Balmer, R.T. 1978. ‘The operation of sand clocks and their medieval development’ in Technology and Culture 19(4): 625–632. Image Credits Detail of Temperance, Ambrogio Lorenzetti. Zenodot Verlagsgesellschaft mbH, GNU Free Documentation License, via Wikimedia Commons 24 inch hour glass with baluster supports. Unknown maker. Unknown Date. Mr. P. Webster, Science Museum Group © The Board of Trustees of the Science Museum, CC BY-NC-SA 4.0, https://collection.sciencemuseumgroup.org.uk/objects/co667/24-inch-hour-glass-with-baluster-supports-hourglass