Zu Chongzhi (祖冲之) had a thing for circles. In fact, he knew his way around an ellipse better possibly than gravity itself.
Such was the extent of Zu’s influence, this Great Nanjinger had parks, roads and schools named after him. Commemorative silver coins have even been struck in his image. Above us in the heavens, Zu’s name has been given to asteroids and craters.
And as we will see, the modern automobile industry owes him a debt of gratitude too.
Zu was the mathematician of his day, but he also had a keen interest in natural science and literature, philosophy and astronomy. In retrospect, we might today describe Zu as the essential link between mathematics and astronomy.
Born in 429 CE, when Nanjing went by the name of Jiankang, Zu’s ancestral home was Xishui County in Hebei Province. The family settled in our neck of the woods after an en-masse migration brought on by the outbreak of war.
With his grandfather a master of civil engineering and a family involved in astronomical research, Zu’s exposure to astronomy and mathematics brought about in him a love for numbers.
Yet, he was also a revolutionary thinker who wished not to blindly accept conclusions of the ancients. His talent earned him much repute as an astronomer who calculated time values with unprecedented precision.
As a youth, Zu successfully predicted four solar eclipses over a 23 year period. His method utilised Zu’s own calculation for the length of the moon’s nodical period (draconic month) as 27.21223 days. We know today the actual number to be 27.21222 days.
Such findings also paved the way for Zu’s calculating of the planet Jupiter’s year. He found it to be 11.858 Earth years. Today’s astronomy puts it at 11.862 years. That’s 1,500 years of progress for you.
Zu also calculated the orbits of Earth, Venus, Mars and Saturn.
No wonder, therefore, that the far side of the moon sports a small impact crater named “Tsu Chung-Chi” (one of many photographed by Luna 3 in 1959; politics of the time dictated that the list include an American and a Chinese) and that “1888 Zu Chong-Zhi” is the alternative name for asteroid “1964 VO1”.
In the realm of mathematics, as the Sheng-Ming reign period (477–479 CE) was coming to an end, Zu found himself commissioned to perfect the “south-pointing chariot”.
The British scientist and historian of the time, Joseph Needham, wrote that, until Zu, “These vehicles, constructed as they had been by barbarian (Qiang) workmen, did not function particularly well. Though called south-pointing carriages, they very often did not point true, and had to negotiate curves step by step, with the help of someone inside to adjust the machinery”.
Without Zu’s solution, a precision three-gear differential, not only would the south-pointing chariot not have been perfected, we would also not have the cars we love driving around in so much today.
More than a millennia and a half ago, this Great Nanjinger brought to the world many of its first modern inventions and discoveries. Zu’s lasting legacy however, would be a feat that was not to be surpassed for 800 years; the calculating of pi to seven decimal places, somewhere between 3.1415926 and 3.1415927.
