古人在确信大地是一个球体后。又对整个地球的大小产生了浓厚的兴趣。可是地球那么庞大,用什么方法来“量”呢? 远在公元前200多年,古希腊学者埃拉托色尼第一次用测量的方法推算出地球的周长。他是在担任亚历山大城图书馆馆长期间完成这一工作的。首先选取两个地点观察夏至日这一天太阳的位置:一个是亚历山大城以南500英里(约800km)的阿斯旺,那儿有一口深井,这天正午观察到太阳能够直射井底,说明当天太阳在阿斯旺 The ancients believed that the earth was a sphere. It also has a keen interest in the size of the entire earth. However, the earth is so large. What method does it use for “measures?” As far back as 200 BC, the ancient Greek scholar Eratosthenes calculated the circumference of the earth for the first time by means of measurement. He completed this work while serving as the director of the Alexander City Library. First, select two locations to observe the position of the Sun on the summer solstice day: One is Aswan, 500 miles south of Alexandria, where there is a deep well. At noon on this day, it was observed that the sun was able to directly reach the bottom of the well. In Aswan