速度计

In the third century B.C. in Alexandria, the Greek scholar Eratosthenes relied on both geometry and reports of the sun's annual appearance almost directly over Aswan to calculate Earth's circumference, arriving at an estimate close to the actual distance.

在亚历山大公元前第三世纪，希腊学者 Eratosthenes 依据几何学和每年太阳出现在阿斯旺差不多正上方的记录来计算地球的周长，估计的数字接近实际距离。