A Timeline of timekeepers
Keeping time: Kruti Shrotri looks at the different timekeepers our civilisation has used over the last five thousand years.
Sundial The sundial is the earliest known timekeeping device. The first known sundial dates to over five thousand years ago, and consisted of only a vertical stick. The shadowcasting part of a sundial is known as the gnomon; in traditional sundials, the gnomon tends to be a triangle, such that its hypotenuse is parallel to the Earth’s axis.
Candle Clock The earliest mention of the candle clock dates back to the 6th century, but it is usually attributed to Alfred the Great who lived a few centuries later. His candle clock comprised of six candles, each twelve inches high. One inch of the candle would burn in approximately 20 minutes such that six candles would burn in 24 hours.
Mechanical CLock Clepsydra A clepsydra measures time through the gradual flow of liquid. The oldest specimens found were Egyptian, dating back to the 14th century BC. These used water. However, since water freezes at 0°C, later versions used mercury instead, which freezes at a much lower temperature of -38°C. Galileo used a mercury clepsydra in as late as the 16th century in his experiments with falling bodies.
Mechanical clocks have been used since the 8th century. They tended to be driven by water, and later by weights. Soon after 1600, Galileo discovered that the motion of a pendulum could be used to regulate clocks, but it wasn’t until 1656 that Chistiaan Huygens built the first pendulum clock. These increased timekeeping accuracy from around 15 minutes per day to 15 seconds per day.