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张衡 Zhang Heng (AD 78-139) - Inventor of the seismometer
By Zhang Ciyun |
April 24, 2011, Sunday
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Print Edition
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Living during the Eastern Han Dynasty (AD 25-220), Zhang Heng was one of China's greatest scientists. Even today, he is still remembered as a great astronomer, mathematician, geographer, inventor and poet.
Born into a declining landlord family, Zhang became interested in celestial phenomena when he was young. While helping his mother in a field, the boy noticed his shadow was longer in early morning but became very short at noon. When he saw his shadow becoming short, he would remind his mother to go home and prepare lunch.
When he was 10, Zhang was already steeped in the classics about astronomy and calendars. When he was 16, he began to travel around the country to further his studies.
He later served the imperial court under the reigns of Emperor An and Emperor Shun as an astronomer to help keep records of celestial events and maintain calendars.
Meanwhile, Zhang concentrated on his research in astronomy, geography and mathematics.
In his treatise, namely Ling Xian (Mystical Laws), Zhang explained that the moon moves around the Earth, but it doesn't illuminate. It only reflects the light from the sun. He also described the nature and phenomena of solar and lunar eclipses.
Later, he invented the Celestial Globe, the world's first water-powered armillary sphere. Through complicated gears, the sphere would make one rotation a year and could also demonstrate the waxing and waning of the moon.
Zhang asked his colleagues to record its movement and then compare it with the actual movement of celestial bodies. It was nearly a perfect match.
Due to the fact that China had always suffered from devastating earthquakes, Zhang created a "Houfeng Didongyi," an instrument for measuring seasonal winds and earth movement.
Today, the exact mechanics are unknown because the instrument was lost in history, but according to descriptions in other historical literature, it was a bronze cylinder with a diameter of about two meters. There were eight bronze dragons attached to the vessel body, each facing a different direction. Each dragon had a bronze ball in its mouth and on the table, there were eight frogs with gaping mouths, waiting for the ball to drop.
The device was very sensitive to vibration. When it detected an earth movement, the ball in the mouth of the dragon facing that earthquake direction would drop into the mouth of the frog below.
One day in AD 138, the dragon facing the northwest released its ball, but people in the capital didn't feel anything. Two days later, a messenger rushed into the capital and reported to the emperor that a powerful earthquake hit a place about 500 kilometers to the northwest, causing severe devastation there.
In mathematics, Zhang improved ancient Chinese calculation of pi (?) to the estimated value of the square root of 10 or 3.1622. He also produced a device that could measure the exact length of "li," the Chinese distance equal to half a kilometer. It was believed to be the first odometer in the world. The great inventor also left behind a number of widely acclaimed poetry and prose.
Born into a declining landlord family, Zhang became interested in celestial phenomena when he was young. While helping his mother in a field, the boy noticed his shadow was longer in early morning but became very short at noon. When he saw his shadow becoming short, he would remind his mother to go home and prepare lunch.
When he was 10, Zhang was already steeped in the classics about astronomy and calendars. When he was 16, he began to travel around the country to further his studies.
He later served the imperial court under the reigns of Emperor An and Emperor Shun as an astronomer to help keep records of celestial events and maintain calendars.
Meanwhile, Zhang concentrated on his research in astronomy, geography and mathematics.
In his treatise, namely Ling Xian (Mystical Laws), Zhang explained that the moon moves around the Earth, but it doesn't illuminate. It only reflects the light from the sun. He also described the nature and phenomena of solar and lunar eclipses.
Later, he invented the Celestial Globe, the world's first water-powered armillary sphere. Through complicated gears, the sphere would make one rotation a year and could also demonstrate the waxing and waning of the moon.
Zhang asked his colleagues to record its movement and then compare it with the actual movement of celestial bodies. It was nearly a perfect match.
Due to the fact that China had always suffered from devastating earthquakes, Zhang created a "Houfeng Didongyi," an instrument for measuring seasonal winds and earth movement.
Today, the exact mechanics are unknown because the instrument was lost in history, but according to descriptions in other historical literature, it was a bronze cylinder with a diameter of about two meters. There were eight bronze dragons attached to the vessel body, each facing a different direction. Each dragon had a bronze ball in its mouth and on the table, there were eight frogs with gaping mouths, waiting for the ball to drop.
The device was very sensitive to vibration. When it detected an earth movement, the ball in the mouth of the dragon facing that earthquake direction would drop into the mouth of the frog below.
One day in AD 138, the dragon facing the northwest released its ball, but people in the capital didn't feel anything. Two days later, a messenger rushed into the capital and reported to the emperor that a powerful earthquake hit a place about 500 kilometers to the northwest, causing severe devastation there.
In mathematics, Zhang improved ancient Chinese calculation of pi (?) to the estimated value of the square root of 10 or 3.1622. He also produced a device that could measure the exact length of "li," the Chinese distance equal to half a kilometer. It was believed to be the first odometer in the world. The great inventor also left behind a number of widely acclaimed poetry and prose.
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