答:我国古代除用地支来标明时间外,也用地支来标明地球上的方向:东为卯,南为午,西为酉,北为子。子午线,就是地球南北极连线,即经线。测出了经线的一度长,就可以知道地球的周长和体积了。早在战国,《周髀算经》根据“盖天说”,就有“正南千里,勾一尺五寸;正北千里,勾一尺七寸。……周髀长八尺,勾文损益寸千里”的记载。这就是“日影千里差一寸”的最早记录,也就是人们最早对于午线长度的概念。“日影千里差一寸”的观点,在两汉时期甚为 A: In ancient times, in addition to the use of land to indicate the time of the branch, but also to support the earth to indicate the direction of the earth: the east d, the south afternoon, the west unitary, North son. Meridian is the connection between the North and South poles of the Earth, that is, the warp. Once the longitude of the warp has been measured, the circumference and volume of the earth can be known. As early as in the Warring States period, according to “Gai Tian said,” there is “a thousand miles south, hook a foot five inches; a thousand miles north, hook a foot seven inches. Profit and loss in thousands of miles ”record. This is the earliest record of “a thousand miles in a thousand miles of a Japanese shadow”, that is, one of the earliest people’s concepts of the length of a meridian. The concept of “thousands of miles in a thousand miles” is very good in the Han Dynasty