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Candle Clock: Studying its History, Facts, and Limitations

Candle Clock: History, Facts, and Limitations
The candle clock is an ancient invention, which was one of the early attempts made by man at measuring time. We shall discuss some of the major facts about the candle clock.
Satyajeet Vispute
Last Updated: Mar 26, 2018
Alternate Use
A candle clock could easily be converted into a timer by inserting a heavy nail into it at the desired interval. Thus, when the candle would burn down to that point, the nail would clatter down onto a metal plate at the base of the candle, signaling the end of the time-interval.
Can you imagine what it would be like to live in a world where there were no clocks, watches, or any other means of telling the time of the day? Maybe it wouldn't be so bad, after all! You could get up late and reach your school or office whenever you wanted! Wouldn't that be cool? But then, consider this - with no means of telling the time that has elapsed, your teacher or boss could also have you studying or working for as long as they liked! That wouldn't be so cool now, would it?

There is no denying that we all share a love-hate relationship with the various timekeepers around us. However, their importance in our lives simply cannot be undermined. Since ancient times, people everywhere have been developing all sorts of instruments for tracking the progress of time. One such interesting instrument was the candle clock, which was used for time-keeping since way before the advent of the mechanical clock. What it is and how does it work? Let's find out.
How Does a Candle Clock Work
Working of Candle Clock
The above illustration demonstrates the working of a typical candle clock.

As can be seen, a candle clock uses a candle as its main element for showing the passage of time. It is made out of a particular type of wax, whose rate of burning is known. The height and width of the candle is fixed accordingly, so that it may be able to accurately show the passage of the required duration of time.

This candle has evenly spaced markings on it, which are usually accompanied with numbers that represent the different intervals of time. Thus, when the candle burns down to a particular marking, the accompanying number indicates the duration of time that has elapsed since it was first lit.

The positions of the markings and the values of the corresponding intervals are carefully fixed by using the knowledge of the rate of burning of the candle. For example, if a candle burns down an inch in 15 minutes, then markings can be made at 1-inch intervals starting from the top end. Thus, when the candle burns down an inch, the user would know that 15 minutes have elapsed, when it burns down 2 inches he/she would know that 30 minutes have gone by, and so on.

In the illustration shown above, each interval represents a duration of 10 minutes. Thus, after being lit, when the candle burns down to the 2nd mark, it indicates that a duration of (2 × 10) = 20 minutes has elapsed. Similarly, when it burns down to the 3rd mark, 30 minutes has elapsed.
History of the Candle Clock
No one can tell for certain when the candle clock was invented or who invented it. The earliest known reference is found in a poem by the Chinese poet and thinker You Jiangu (520 CE). His device comprised six candles, all of which were 12 inches high, and divided into 12 sections of one-inch each. The candles also had the same girth, and the same kind of wax was used to build all of them. Each candle would burn completely in four hours, so each marking represented 20 minutes. The candles were enclosed inside a wooden case to protect them from being blown out. The cases had transparent horn panels on the sides to allow the user to observe the candles inside. You Jiangu used these candles to tell time during nighttime.

In Europe too, similar devices were used to measure time in medieval churches, and even earlier by King Alfred the Great of England. He was able to measure time by counting the number of candles of a specified size that were completely burnt. Later, he even made use of a graduated candle for time measurement.
A notable use of the candle clock was made by Al-Jazari in 1206 AD. His candle clocks are considered to be the most sophisticated design that was ever created. They included a dial to display the exact time, and for the first time, a bayonet fitting and a fastening mechanism that is still being used in present times.
These clocks used a weight, pulley, and counterbalance arrangement, to move a series of automata, which displayed the time. As the candle would burn, it would become lighter in weight, which caused the counter-weights to move, and accordingly operate a complex mechanism which would then display the time.
Advantages of the Candle Clock
Candle clocks were used at a time when mechanical clocks had not been invented. They provided people, back then, with the means of measuring the time duration that had elapsed.

Since the rate of burning of the wax in a candle is almost constant, these clocks were able to almost accurately indicate the passage of time.
In ancient times, people relied on the position of the Sun to tell the time of the day, and that of the Moon to tell the time at night. However, both these methods would fail when the skies were cloudy. In such instances, the candle clock would prove to be a handy tool for accurate time measurement.
Limitations of the Candle Clock
1) The candle clock can only be used to tell the time interval that has elapsed, and therefore, cannot be used to tell the exact time of the day.

2) If the candle is blown out before it reaches a mark, then it would be difficult to tell precisely how much time has gone by even, if it is re-lit.

3) Imperfections in the construction introduces errors in the time measurement. Also, uneven melting of the wax can result in a false reading.
The invention of the candle clock provided the ancients with a near-accurate way of measuring time. It has been used for a long time, and even though it has today been discarded in favor of mechanical and digital clocks, it will always hold a place of historic significance, as being one of the first timekeeping devices.