【英语时差8,16】丈量地球的棍子

On our last program we discussed a simple experiment run by an Alexandrian named Eratosthenes in the third century B.C.    By noting that, at the same time of day, sticks in the ground cast different-length shadows depending on whether they were in a northern or a southern town, Eratosthenes deduced that the surface of the earth must be curved -- and thus that the earth itself must be shaped like a ball.

This is an impressive enough achievement, but Eratosthenes didn't stop there. Realizing the earth was round, he then applied¹ a little geometry. He imagined his two sticks -- one in the northern town of Syrene, one in the southern town of Alexandria -- as lines extending downward until they meet at the center of the earth.

Drawing more lines coming straight down to represent sunlight, Eratosthenes moved one stick along the outside of the circle until the shadow it would be casting matched the shadow his stick actually made. Now he knew how much of the circle extended between Syrene and Alexandria -- about seven degrees.

There's no fancy way to get around the next step: Eratosthenes needed to know the actual distance from Alexandria to Syrene. So he paid some camel caravan² drivers to go from one town to the other and tell him how far it was. A few achy-footed camels later the answer came back: 500 miles. So, if 500 miles equals 7 degrees of the circle, the whole circle must be 25,000 miles.

Eratosthenes' answer, deduced with nothing but two sticks, some tired camels and a brain, is within a few percent of being correct.  

1 applied   

adj.应用的；v.应用，适用

参考例句：

• She plans to take a course in applied linguistics.她打算学习应用语言学课程。
• This cream is best applied to the face at night.这种乳霜最好晚上擦脸用。

2 caravan   

n.大蓬车；活动房屋

参考例句：

• The community adviser gave us a caravan to live in.社区顾问给了我们一间活动住房栖身。
• Geoff connected the caravan to the car.杰弗把旅行用的住屋拖车挂在汽车上。