The ancient art of telling time with fire and smoke

In China, the use of incense smoke to tell the time dates back to the 6th century CE. Incense would be lit at the bottom of a maze and burn through it, with outlets to vent smoke and tell the time.

Different scents may even have been used along the maze to tell the current time with a puff. And there were even incense alarm clocks where incense burned through strings and dropped metal balls into a bowl to sound the alarm.

Incense timers were used in China in the 21st century by coal miners to gauge the length of time spent underground.

From JSTOR Daily:

According to historian Andrew B. Liu, incense had been used to measure time since at least the 6th century, when the poet Yu Jianwu wrote:

By burning incense [we] know the hour of the night,
With graduated candle [we] confirm the countdown of the watch.

The Incense Clock takes the core concept – combustion timing – and elevates it to a magnificent new level of complexity. When examining the example held by the Science Museum, I was struck by its small size: no bigger than a cup of coffee. Yet its small compartments are neatly packed with everything it needs to function. In the bottom tray, you’ll find a bite-sized shovel and shock absorber; above, a pot of wood ashes to trace the path of the incense; then, stacked on top, a set of stencils for tracing the mazes. As Silvio Bedini, historian of scientific instruments, explains in his in-depth study of the use of fire and incense for the measurement of time in China and Japan, the variety allows for seasonal variations: longer paths to burn through the endless winter nights, while shorter paths serve for the summer.

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