Time
Writing and Calculation
Using Numbers
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An "hour" in ancient Egypt was longer or shorter at different times of the year. The Egyptians divided day and night into twelve egual segments, measuring from sunrise to sunset and sunset to sunrise, so a day hour was longer and a night hour was shorter in summer than in winter. Time was measured by filling a container called a water clock with water, which dripped at a constant rate from a hole at the base of the clock. Inside, circles corresponded to the water level as each hour passed. We are not sure whether the Egyptians were the first to invent water clocks, but this way of measuring time was used until mechanical clocks were invented in medieval Europe.
