First hourglass

The first hourglass (also known as sandglass or sand clock), was said to have been invented by a French monk called Luitprand in the 8th century CE, but there is no evidence to support this claim. It seems likely, instead, that the device was first developed in the eleventh or twelfth century, by either Islamic or European makers. Concrete evidence of this revolutionary new form of clock, which measures time by the descent of sand or other free-flowing powders from one glass bulb to another, first appeared as a detail in a fresco in Siena’s Palazzo Pubblico, painted by Ambrogio Lorenzetti in 1338. European ship inventories, later in the 14th century, also contain evidence of sandglasses. Arriving in time for the so-called “Age of Discovery”, the hourglass was ideal for ocean travel because the bobbing waves didn’t affect its accuracy.

In Lorenzetti's painting, the hourglass is pictured in the hands of a figure intended to represent "temperance" as a civic virtue. The use of the device as a symbol confirms that it was already a well-known and familiar object to the public.