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The History of Hourglasses
by Kelsey Erin Shipman
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Overview
Hourglasses originated in Italy and were widely used as household instruments and on sailing vessels. They could be cheaply made for use at home, or wildly expensive -- decorated with precious metals and jewels -- for royalty. Hourglasses have remained a trusted method of time measurement and are still valued for their artistry today.
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History
By the first half of the 14th century, hourglasses were a common form of time-keeping in Italy and other parts of Western Europe. A series of allegorical frescoes painted by Ambrosio Lorenzetti in 1338 feature the earliest known illustration of a sand-glass (as they were commonly called). It looks similar to modern hourglasses except for its straight sides. Hourglasses have been referred in literature, royal records and music throughout the ages.
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Origin
Though theories abound, there is no factual evidence supporting the exact origin of hourglasses. There is much evidence of their use at sea, specifically to measure the distance traveled by a ship in the open ocean. One theory is that the hourglass was invented for this purpose around 1100 A.D., along with the invention of the magnetic compass, in the Italian ports of Amalfi, Pisa, Genoa and Venice.
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Features
Though sand-glasses are relatively easy to make, there are some essential components. The glass ampules must be carefully hand-blown with a small but sturdy aperture between the two parts. The angles made by the cones of the ampules should be equal to the angle of repose of the sand. It is critical that the sand used is very fine, completely dry and free of any impurities, to prevent clogging.
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Use
By the end of the 14th century, the sand-glass was a common piece of European household equipment, used for measuring time. It was a routine duty of a housewife to take the two ampules apart, as they were made in two separate pieces at that time, and fill them with a homemade recipe of "sand."
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Size
The size of the sand-glass determines its time-keeping. Small sand-glasses have to be turned once or twice each hour. However, larger ones, such as the one ordered by Charlemagne, had to be turned only once every twelve hours. Some had a small dial with a pointer that could be advanced every time the glass was turned. Whatever the size, someone had to keep watch in order to turn the sand-glass at the exact moment the last sand grain dropped.
