Tickipedia: 1200AD-1400AD
Time, one of the seven fundamental physical quantities in the International System of Units, is a dimension in which we all exist. It marches on as certain as the sun rises and sets, and its behaviour has fascinated scientists as far back as history recalls. In this edition of Tickipedia, we discover how our horological predecessors looked to the stars.
Inventor Abu’l Izz Isma’il al-Jazari released a collection of his ideas, including the Elephant Clock shown here, in the 1206 book Automata
Having explored the burning of candles at both ends in order to tell the time during the twelfth Century, the story of timekeeping looks upwards, as astrological clocks charted the positions of the sun, moon, planets and stars to determine time according to local latitude.
Over a millennium after the first astrolabe (an instrument used to take astronomical measurements) was invented, Muslim astronomers were among the first to develop clockwork versions, constructing astronomical clocks for their mosques and observatories. Examples include al-Jazari’s water-powered astronomical clock in 1206, an offering that wasn’t a merely practical invention; eleven feet in height, the complex castle clock featured a number of musical and moving automata, a display of the solar and lunar paths and doors which opened upon the hour to reveal a mannequin. Considered to be an early example of a programmable analog computer, it could be adjusted to account for the changing day lengths throughout the year. Less visually impressive but no less important were the sophisticated geared astrolabe mechanisms designed by Muhammad ibn Abi Bakr in 1235, and the astrolabic clocks of Islamic astronomer and religious timekeeper Ibn al-Shatir which followed in the early 1300s.
In China, the astronomical clock established itself some time earlier, with astronomer, horologist and mechanical engineer Su Song creating the clock tower of Kaifeng in 1088. This incorporated an escapement mechanism, as well as the earliest known endless power-transmitting chain drive, which drove the armillary sphere. Also known as a celestial globe, the armillary sphere displayed the positions of the stars, while tablets showed the time of day. The clock was eventually dismantled by the Jin army and transported to Yangjing (now Beijing), although once there they were unable to reassemble it, instead ordering Su Song’s son Su Xie to build an exact replica.
In Europe, Strasbourg Cathedral first housed an astronomical clock in the 1350s, while the central portion of Prague’s famous Old-Town Hall clock was completed in 1410, with a skeletal depiction of Death striking the time. The timekeeping value of the astronomical clocks created before the 16th Century was not what it could have been; mainly using simple verge and foliot escapements, there was a margin of error of at least half an hour a day. Despite this, these clocks were built as exhibitions of skill and wealth, made to display the heavenly bodies themselves, and that alone is worth losing thirty minutes for.
