Humboldt State University ® Department of Chemistry

Richard A. Paselk

The Development of the Clock and the Concept of Time in the Middle Ages

(Summer 1997)


The various instruments used for keeping time are all measuring devices and thus in some senses scientific instruments. The most extraordinary of these devices is the mechanical clock: a most remarkable and in some ways unexpected instrument. Certainly it was the most complex scientific instrument of the middle ages, and in many ways seems unprecedented.
It is thought that the mechanical clock was invented in Western Europe around 1300 CE. The exact date is difficult to establish because no clocks from this period are extant, and because the terms used to describe early clocks were also used to describe clepsydra or water-clocks. One of the most remarkable aspects of the clock is that some of the earliest known examples were also incredibly complex. An example is the Astrarium completed by Geovanni di Dondi, an Italian astrologer/physician in 1364. This clock is well known because di Dondi left detailed plans for its construction (at least three replicas exist: at the Science Museum, London; at the Smithsonian, Washington D.C.; and one owned by IBM Corp.). This clock had seven faces which displayed the positions of the stars (as on an astrolabe's face), the positions of various planets, the moon's position etc., it was a complex, multiple-display astronomical device. This device is unlikely to have arisen from nowhere. It turns out we now know that astronomical gearwork goes far back into antiquity (e.g. the Antikythera device, an astronomical computer of c. 50 BCE, a geared Byzantine Sundial/calendar of c. 520 CE, and various geared astrolabes of c. 1200-1300 CE).
But gearwork is only half of the problem of the origin of the clock-the other is the origin of the escapement. This mechanism truly seems to be a medieval invention. Are there again precedents? First alarm bells of medieval timers had an oscillating action. Second, we know the Chinese invented an escapement of a different sort (C. 1090), but there is no evidence of its diffusion, and indeed the technology was quickly lost in China itself.
We have been dealing with technical aspects of the clock's origins. What about need-who cared? First the Monastic orders: there were specific requirements for times of prayer. But these times were better measured with sundials or water clocks because they needed unequal hours, that is hours proportional to day length, which in Northern Europe varies significantly with the season! (Of course in Northern Europe the sun is often obscured by clouds and water clocks may freeze in the winter!) And, until the invention of the pendulum clock, water clocks were capable of greater accuracy! The second group would be astronomers and medical astrologers. They wanted equal hours, the hours of the planets and stars-God's hours. For them the clock was a conscious model of the solar system. It could then of course also become a valuable theological model once it was perfected.
The clock quickly became one of the great symbols of the medieval period. Building a clock was their equivalent of the Apollo Project: an incredibly expensive venture requiring the services of the most highly trained scientists and technicians of the culture and a large investment of material.
Examples of Some Clocks and Time Keeping Instruments Typical of the Middle Ages
  1. DSL= Landes, David S. Revolution in Time. Belnap Press, Cambridge Mass. (1983).
  2. GLT= Turner, Gerard L'E. Antique Scientific Instruments. Blanford Press. Poole (1980).

Workshops Medieval Science & Scientific Instruments


© R. Paselk

Last modified 6 August 1999