英语听力文摘 English Digest 192、光速与洲际高速

　　世界上跑得最快的是什么？答案是光速。它每秒能跑186,280英里。因为即使在太空中，光速也大致相同，所以光年也就用于描述不同星球之间的距离。记住了哦，光年是距离单位，不是时间单位。同时光这么快的速度又对我们有什么意义呢？一起听听吧。
If you’re driving on an interstate highway, the only thing keeping you from going faster than the speed limit is your sense of civic¹ duty, or perhaps that police car up ahead.
There’s one speed limit, however, that most scientists agree nothing will ever break.  That’s the speed of light:186,280 miles per second.

　　As it travels through deep space, light moves at exactly this speed, no more and no less.The speed of light is so reliable, we even use it to measure distances between the stars.
If it takes starlight fifty years to reach us, we say that this star is fifty light years away.
You might be surprised to learn, however, that light itself does not always travel at the speed of light.Our interstate highways generally have a higher speed limit, but once you enter a city or residential² street, the speed limit lowers.
Likewise³, light travels at its maximum speed through a vacuum⁴ the interstellar highway but it slows down when it enters air, water, or some other medium.
Through air, light moves a hint⁵ slower:  forty miles per second less than its maximum speed.Through glass, light moves almost eighty thousand miles per second slower.
Light moves more than a hundred thousand miles per second slower through a diamond less than half its speed in a vacuum.
Light moves so quickly anyway, do we ever notice this change in speed? Actually, we do.When light slows down it also bends slightly.This is know as refraction.
Lenses⁶ use the lower speed limit of light in glass to bend and focus the light.If light always moved at it’s maximum speed, none of our telescopes, eyeglasses or even our eyes themselves would ever work.

1 civic   

adj.城市的，都市的，市民的，公民的

参考例句：

• I feel it is my civic duty to vote.我认为投票选举是我作为公民的义务。
• The civic leaders helped to forward the project.市政府领导者协助促进工程的进展。

2 residential   

adj.提供住宿的；居住的；住宅的

参考例句：

• The mayor inspected the residential section of the city.市长视察了该市的住宅区。
• The residential blocks were integrated with the rest of the college.住宿区与学院其他部分结合在了一起。

3 likewise   

adv.同样地，照样地；也，又

参考例句：

• The explorers had to undergo much suffering.探险者不得不忍受很多困苦。
• The planes have to undergo rigorous safety checks.飞机必须经过严密的安全检查。

4 vacuum   

n.真空，空间，真空吸尘器；adj.真空的，产生(利用)真空的；v.用吸尘器打扫

参考例句：

• Sound waves will not travel through a vacuum.声波在真空里不能传播。
• He sells vacuum cleaners.他经销真空吸尘器。

5 hint   

n.暗示，示意；[pl]建议；线索，迹象；v.暗示

参考例句：

• He gave me a hint that I was being cheated.他暗示我在受人欺骗。
• He quickly took the hint.一点他就明白了。

6 lenses   

n.透镜，镜头( lens的名词复数 )；眼睛中的水晶体

参考例句：

• a pair of glasses with tinted lenses 一副有色镜片眼镜
• Wash the lenses in saline solution. 用盐溶液清洗镜片。