Tickipedia: 1000AD-1200AD

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 light and time are inextricably linked.

Turkish polymath Al-Jazari, here pictured with his counterweight candle clock mechanism

In previous editions, we've noted that sundials are one of the most ancient forms of timekeeping known to historians, and have been found among the earliest remnants of human culture. The principle is very simple: the Sun's passage across the sky creates a shadow that moves at a constant pace, showing the time over the course of the day. Even in antiquity, many cultures had created dials to a high degree of accuracy, but there remained a problem: the duration of the Sun's journey varies over the year.

For many centuries, people simply put up with having hours that were longer in summer than in winter. For agricultural communities, the exact length of each hour was unimportant anyway; what you really needed to know was how much sunlight you had left. But this all changed in 1371 when a brilliant Arabic astronomer with the suitably epic name of Ala Al-Din Abu'l-Hasan Ali Ibn Ibrahim Ibn al-Shatir used complex mathematics to make an important discovery: if you align the object casting the shadow (official term: gnomon) with the exact tilt of the Earth's axis, then the shadow will move at exactly the same rate on every day of the year. Funny to think that, before this, there had never been unchanging, uniform hours recorded on sundials. The concept didn't even become mainstream in Europe until the 1500s.

Meanwhile, other kinds of clocks that lent themselves more naturally to uniform hours were coming on leaps and bounds—again, largely thanks to advanced Arabic science. A key timekeeper in medieval times was the candle clock, which utilised the convenient property of wax to melt at a consistent speed, and had the added bonus of working at night or in miserable English weather.

In fact, it is a famous Englishman who is most closely associated with the candle clock. The semi-mythical warlord, fugitive and burner of cakes Alfred the Great is credited with bringing the candle clock to widespread use in Europe, although like many groundbreaking European inventions, it was known to ancient Chinese dynasties at least as early as 520 AD.

Candle clocks remained fairly simple for a long time. The idea is that your light source also tells the time by observing the quantity burnt. You can even add a handy alarm function by jabbing it with an old nail—when the candle reaches the point where you stuck it, it will fall out and clatter onto the dish below.

Serious and much-needed upgrades to this design arrived in 1206 courtesy of a Golden Age Turkish polymath with another improbably long name, but who was known to his friends as Al-Jazari. His great contribution was the idea that instead of burning down, the candle could burn up. By attaching a counterweight to the bottom and a cap at the top with a hole for the wick, the candle was pushed up as it melted, and this allowed its timekeeping consistency to be connected to a larger machine. In this way, Al-Jazari was able to build large and impressive mechanical clocks and automata that didn't require any water—a major boon for arid countries like Turkey.