Eratosthenes computed the shadow in alexandria to be 1 / 50 of a full 360-degree circle .
埃拉托色尼计算出在亚历山大城影子的角度是360度的1/50。
The greek mathematician , eratosthenes , had accurately deduced that the world was approximately 25000 miles in diameter .
希腊数学家埃拉托色尼，曾准确地推断地球直径约为25000公里。
Eratosthenes knew that at noon on the day of the summer solstice , the sun was observed to be directly overhead at syene ( modern-day aswan ) : you could see it from the bottom of a deep well , and a sundial cast no shadow .
