Let's Talk Clocks

What constitutes a "clock"? The Latin horologium could refer to a clock or a timepiece of a sundial or the building or structure designed to support any of those.

Modern horology, the study of the measurement of time, distinguishes clocks which mark time by striking something (the word "clock" comes from French cloche, "bell"), whereas a timepiece does not. So a timepiece can mean a watch, a sundial, a clepsydra, or an hourglass, etc.

The sundial was likely the earliest way to measure time: a shadow on a flat surface displays the progression of the sun.

The clepsydra (Greek κλεψύδρα, literally "water thief"), was used in Babylonb, Persia, and Egypt as far back as the 16th century BCE. The simplest form is a bowl or other vessel with a hole from which the water drains, and markings to match drainage levels with the passage of time. The Greco-Roman world devised an in-flow (rather than out-flow) method which, as water filled a container, would trigger a sound, creating an "alarm clock." Water clocks evolved that used gears and escapement mechanisms to produce greater accuracy.

An escapement is a gear mechanism that ticks forward and back to cause another piece to advance. The illustration shows how this works in a pendulum clock, advancing the hands. The use of the escapement was crucial to the development of mechanical clocks, which started to appear in the 14th century in Europe. (Not in the 10th, built by Gerbert d'Aurillac.)

Let's not neglect candle clocks. A Chinese poem written in 520CE by You Joanfu mentions a clock marked so that it could be used while burning to measure the passage of night time. The Anglo-Saxons credit Alfred the Great with creating the candle clock. He used squat candles (<5" high) marked at 1" intervals to mark time.

The hourglass was also a common method of measuring time, the earliest depiction of which is in a 1338 painting by Ambrogio Lorenzetti.

The earliest mechanical clock, a clock that did not use water or sand or candles, that used a predictable motion due to the escapement and a pendulum, did not appear until the early 1300s. Norwich Cathedral had a tower clock constructed in the early 1320s. The first known municipal clock that struck on the hours was in Milan in 1336. Over the next few decades, mechanical clocks appeared all over: Old St. Paul's Cathedral, Salisbury Cathedral (still has many original parts!), Wells Cathedral (still with its original face), etc. Detailed descriptions of clock designs by Richard of Wallingford (1292 - 1336) and Giovanni de Dondi (c.1330 - 1338) still exist, though the many clocks they built are long gone.

A king who developed his own timepieces made from candles? He sounds like someone worth looking into.

The Hourglass

Detail, Allegory of Good Government
Ambrogio Lorenzetti, 1338

The hourglass has become a symbol of medieval technology, one of our first attempts to quantify and measure time. We know it existed in the 14th century, from a 1338 fresco by Ambrogio Lorenzetti (c.1290 - 1348) in which the allegorical figure of Temperance holds one (Temperance, after all, is about taking a "measured" response to something, rather than uncontrolled actions). In 1345, an English merchant's receipts show that he paid for "twelve glass horologes" in Flanders, establishing that they were probably already prevalent and in demand.

Sailors found the sand-filled hourglass a definite improvement over its predecessor, the clepsydra* (the water clock), which was affected too much by the swaying of the ocean. When Magellan (c.1480 - 1521) circumnavigated the globe, his fleet had 18 hourglasses per ship, with a page dedicated to turning each one to keep accurate time.

They were also preferable in the early Middle Ages to clocks, because they did not rely on complicated and delicate machinery that needed frequent maintenance.

Where and when was the hourglass invented? A story that it was invented in the 800s by a monk at Chartres named Liutprand has no evidence to support it. The clue to the origin may be in the construction. The earliest hourglasses used marble dust for the sand. Also, the hourglass required expertise in glass-blowing. The likeliest location for these two features of the hourglass to be brought together is Italy, particularly Venice, where glass-blowing was a highly developed art and marble was readily available.

By the end of the 14th century, hourglasses were so common that the Goodman of Paris, writing a guidebook for his young wife in the 1390s, included a recipe for preparing the sand/dust for an hourglass:

Take the grease which comes from the sawdust of marble when those great tombs of black marble be sawn, then boil it well in wine like a piece of meat and skim it, and then set it out to dry in the sun; and boil, skim and dry nine times; and thus it will be good.

Not only must the hourglass have become common, but its construction was clearly something that could be contributed to by a regular household.

*clepsydra is from the Greek and means "water thief"; they could be very elaborate, but were naturally susceptible to humidity and temperature.