History
By Catherine Rose
A Brief History of Time For thousands of years human beings have used devices invented to measure the passage of time. As the sun moved across the sky, people were able to measure the day’s passing with obelisks and sundials, by monitoring their shadows. Some of the earliest clocks were stone obelisks built by the ancient Egyptians in 3500 BC. Sundials, which show the height of the sun using a shadow-casting rod called a gnomon attached to a marked plate, feature widely across many ancient cultures including in India. The world’s biggest sundial dates from the sixteenth century and can still be visited at Jantar Mantar in Jaipur. Sundials remained in popular use until the nineteenth century. During Shakespeare’s time, people even carried pocket sundials, referred to by the bard in his play As You Like It:“…he drew a dial from his poke [bag].” However, measuring time using the sun is problematic, as it only works during daylight hours when it is not cloudy. To overcome this and
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determine time at night, another method used graduated candles whose measured burn could also calculate passing hours. In around 1400 BC the ancient Greeks built water clocks, but they were probably invented in ancient Egypt. Known as clepsydrae, they basically consisted of two containers, one placed higher than the other. Water would drip slowly from the top container to the bottom, while markers inside the lower container showed how much time had elapsed. Subsequent developments of the water clock resulted in increasingly complex use of floats and gears that moved a hand on a face, anticipating the modern clock. From the seventh century the Chinese not only built huge water clocks but also more accurate timepieces, based on similar principles that employed mercury. In the eleventh century an Arab engineer named Ibn Khalaf Al-Muradi built a water clock with a sophisticated gear mechanism,
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