英语听力文摘 English Digest 184、我们如何知道地球在转？

　　Before Satellite Images, How’d We Know Earth Turned Every 24 Hrs?
在我们有卫星行片以前，我们是如何知道地球一天二十四小时都在转动呢？去听听科学家的说法吧。
The earth turns on its axis¹ every 24 hours — or so we’re taught.  But, before we had pictures from space, how would we prove it to someone?
The rising and setting of the sun and stars in the sky provide pretty strong evidence, but not absolute proof, since they could be moving and the earth standing² still!
One piece of evidence from right here on the ground is the behavior of falling objects.  Newton’s laws of gravity and motion predict that a dropped object on a rotating earth should fall slightly toward the east as it drops.

　　Here’s why.  Suppose you have a ball suspended from the top of a tower.  Because the earth turns, the top of the tower travels just a little faster, in terms of miles per hour, than the ground directly below, just like the edge of a phonograph record travels faster than a point near the center.
If you drop the ball, gravity will pull it toward the center of the earth, but will not diminish that extra eastward³ speed.  So as the ball falls it’ll outrun the ground and land slightly east of the straight-down point.
Edwin H. Hall, a Harvard University physicist⁴, looked for this effect in 1902.  Working in an enclosed tower, he dropped one-inch bronze balls from a height of 75 feet into a pan of tallow.
Hall was careful.  He built a mechanism⁵ to release the ball without jiggle or spin, and a cloth tube to protect the path of fall from breezes.  He used high-precision surveying telescopes to measure the position of a plumb⁶ line before each drop, and the position of the ball afterward⁷.  He made a total of 948 drops.
The average eastward deflection was just as predicted by Newton’s laws for a 75-foot tower at the latitude⁸ of Cambridge, Massachusetts about one-seventeenth of an inch.

1 axis   

n.轴，轴线，中心线；坐标轴，基准线

参考例句：

• The earth's axis is the line between the North and South Poles.地轴是南北极之间的线。
• The axis of a circle is its diameter.圆的轴线是其直径。

2 standing   

n.持续，地位；adj.永久的，不动的，直立的，不流动的

参考例句：

• After the earthquake only a few houses were left standing.地震过后只有几幢房屋还立着。
• They're standing out against any change in the law.他们坚决反对对法律做任何修改。

3 eastward   

adv.向东；adj.向东的；n.东方，东部

参考例句：

• The river here tends eastward.这条河从这里向东流。
• The crowd is heading eastward,believing that they can find gold there.人群正在向东移去，他们认为在那里可以找到黄金。

4 physicist   

n.物理学家，研究物理学的人

参考例句：

• He is a physicist of the first rank.他是一流的物理学家。
• The successful physicist never puts on airs.这位卓有成就的物理学家从不摆架子。

5 mechanism   

n.机械装置；机构，结构

参考例句：

• The bones and muscles are parts of the mechanism of the body.骨骼和肌肉是人体的组成部件。
• The mechanism of the machine is very complicated.这台机器的结构是非常复杂的。

6 plumb   

adv.精确地，完全地；v.了解意义，测水深

参考例句：

• No one could plumb the mystery.没人能看破这秘密。
• It was unprofitable to plumb that sort of thing.这种事弄个水落石出没有什么好处。

7 afterward   

adv.后来；以后

参考例句：

• Let's go to the theatre first and eat afterward. 让我们先去看戏，然后吃饭。
• Afterward,the boy became a very famous artist.后来，这男孩成为一个很有名的艺术家。

8 latitude   

n.纬度，行动或言论的自由(范围)，(pl.)地区

参考例句：

• The latitude of the island is 20 degrees south.该岛的纬度是南纬20度。
• The two cities are at approximately the same latitude.这两个城市差不多位于同一纬度上。