Candle clocks

A candle clock

It is not known specifically where and when candle clocks were first used; however, their earliest mention comes from a Chinese poem, written in 520 by You Jianfu. According to the poem, the graduated candle was a means of determining time at night. Similar candles were used in Japan until the early 10th century.^[38]
The candle clock most commonly mentioned and written of is attributed to King Alfred the Great. It consisted of six candles made from 72 pennyweights of wax, each 12 inches (30 cm) high, and of uniform thickness, marked every inch (2.5 cm). As these candles burned for about four hours, each mark represented 20 minutes. Once lit, the candles were placed in wooden framed glass boxes, to prevent the flame from extinguishing.^[39]
The most sophisticated candle clocks of their time were those of Al-Jazari in 1206. One of his candle clocks included a dial to display the time and, for the first time, employed a bayonet fitting, a fastening mechanism still used in modern times.^[40] Donald Routledge Hill described Al-Jazari's candle clocks as follows:

The candle, whose rate of burning was known, bore against the underside of the cap, and its wick passed through the hole. Wax collected in the indentation and could be removed periodically so that it did not interfere with steady burning. The bottom of the candle rested in a shallow dish that had a ring on its side connected through pulleys to a counterweight. As the candle burned away, the weight pushed it upward at a constant speed. The automata were operated from the dish at the bottom of the candle. No other candle clocks of this sophistication are known.^[41]