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[转载]第17课

(2010-12-06 16:50:52)
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原文地址:第17课作者:小脏形象

Text 17 How Homing Pigeons Find Home ?
1. Science seems to be getting closer to answering a very old mystery. Homing pigeons can be taken hundred of miles from their home. When they are let go to fly again, they find their way home. Because of this special ability to find home, pigeons have been used as messengers for hundreds of years. 科学似乎快要找到这一非常古老神秘的问题的答案了.人们可以把信鸽带至离家数百英里的地方.当再将其放飞时,它们能找到回家的路.因其这一特殊的找家本领,鸽子几百年来一直被人们当作送信使者.
2. Today people even keep homing pigeons for racing as a sport. The birds are shipped to some chosen place a few hundred miles away. Then all of them are let go together. The winner is the bird that goes home first. A good racer can make it home 500 miles away in a single day.
当今人们养信鸽甚至只是为了参加竞飞这一体育活动.这些信鸽被送到几百英里之外的某一指定地点.然后将其同时全部放飞.第一个到家的鸽子就是优胜者.一只好的赛鸽一天即可往家飞行500英里开外.
3. The mystery of the homing pigeon is in how it navigates and how it finds home. It may be taken away in a covered-up cage, even a cage that is turned round and round to purposely mix up any sense of direction. To get home, it must fly over country that it has never seen before.
信鸽的神秘之处在于它如何导航、如何找到家的.它可能会被装进遮盖着的箱子带走,箱子甚至被翻过来调过去,故意混淆它的各种方向感.为了能回到家,它必须飞越从未见过的地域.
4. Suppose this were to happen to you? What would you need to find your way home (besides a good pair of legs)? I think I would ask for a compass, which always points north, to help find direction. I would also want a map. If a map shows where my home is, then I can use the compass to point me in the direction toward home. What we are talking about shows the two parts of the problem of the homing pigeon. Much of the study of homing pigeons leads to the idea that pigeons need the same kinds of information. They need to know how to tell direction and they need something like a map to tell which direction is toward home.
假设你遇到这种情况该怎么办?要找到回家的路将需要什么(除了健全的双腿之外)?我认为需要一个指南针,用以辨别方向。我还想要一幅地图。如地图标出了我家所在的位置,那么我会利用指南针为我指出家所在的方位。我们谈论的问题表明了信鸽问题的两要素。对信鸽的深入研究得出了这样结论:信鸽需要同样种类的信息。它们需要知道如何辨别方向,它们也需要地图之类的东西来辨别朝家去的方向。
5. The first part seems to be pretty well answered, and we know of two ways that pigeons tell direction. First, they use the sun. Just getting rough direction from the sun is easy. It rise somewhere toward the east and sets somewhere toward the west. Getting accurate directions from the sun takes more care. You need to pay attention to the time of the year. Then you need to watch the path of the sun closely at each hour of the day. To tell direction accurately from the sun, a person needs to know the exact time.
第一个要素似乎有了相当圆满的答案,我们已晓得信鸽辨别方向有两种方法。首先,它们利用太阳。根据太阳来确定大致方向不难。太阳大致从东方升起,朝西方落下。靠太阳来确定精确的方向则需要更为细心。你要注意全年时间的情况。接下来你要认真观察太阳每小时行经的路线。要靠太阳来精确地辨别方向,你就需要了解准确的时间。
6. Plants and animals that have been studied carefully (including the human) seem to have built-in clocks. These biological clocks, as they are called, usually are not quite exact in measuring time. However, they work pretty well because they are "reset" each day, maybe when the sun comes up.
人们精心研究的所有动植物(包括人在内)似乎都有内在的时钟。这些人们称之为生物钟的时钟计量时间并非十分精确。然而,它们却运行的很好,因为,大概是太阳升起的时候,它们每天都要“校时”。
7. Do pigeons use their biological clocks to help them find direction from the sun? We can keep pigeons in a room lighted only by lamps. And we can time the lighting to make their artificial "days," start at some different time from the real outside day. After a while we have shifted their clocks. Now we take them far away from home and let them go on a sunny day. Most of them start out as if they know just which way to go, but choose a wrong direction. They have picked a direction that would be correct for the position of the sun and the time of day according to their shifted clocks.
鸽子是否利用生物钟来靠太阳帮助确定方向呢?我们可以把鸽子放在一间只用灯光照明的房间里。 我们可以安排光线出现我时间,从不同于外面真实的时间开始,使其成为人工的白昼。过了一段时间,我们已经改变了其生物钟。现在我们带它远离家门,在一个阳光明媚的日子将它们放飞。它们大多立刻启程,仿佛它们明白该走哪条路,不过却飞错了方向。它们选择了根据太阳的位置本来应该是正确的方向,同时根据变化了的生物钟选择了时间。
8. We have talked about one of the more complex experiments that lead to the belief that homing pigeons can tell directions by the sun. What happens when the sky is darkly overcast by clouds and no one can see where the sun is? Then the pigeons still find their way home. The same experiment we talked about has been repeated many times on sunny days and the result was always the same. But on very overcast days those clock-shifted pigeons are just as good as normal pigeons in starting out in the right directions. So it seems that pigeons also have some extra sense of directions to use when they cannot see the sun.
我们已经讨论了导致这一信念的更复杂的一项实验,该信念认为信鸽可以凭太阳辨别方向。可当乌云密布、天色昏暗,谁也看不到太阳在哪儿时,会是什么情况呢?那时信鸽仍能找到回家的路。我们谈到同一个实验已在阳光明媚的日子反复做过许多次,其结果总是相同的。可在乌云蔽日这时那些生物钟已经改变了的信鸽在沿正确的方向起飞前行方面仍像正常的鸽子那样,做得非常好。因而,在看不到太阳时,鸽子似乎还可以利用其所具有的某种别的方向感。
9. Naturally, people have wondered whether pigeons might have a built-in compass -- something that would tell them about the direction of the earth's magnetic field. One way to test that idea would be to see if a pigeon's sense of direction can be fooled by a magnet attached to its back. With a strong magnet close by, anything like a magnetic compass can no longer tell about the earth's weak magnetic field.
自然,人们一直想知道信鸽是否有一种内在的指南针—一个能使其知道地球磁场方向的什么东西。证明这一观点的一种方法是看鸽子的方向感是否会爱缚在它背部的一块磁铁的愚弄。如果把一块磁力很强的磁铁放在近旁,任何像磁性罗盘之类的东西都无法分辨出正确方向。
10. To test the idea, one group of ten pigeons had strong little bar magnets attached to their backs. Another group carried little brass bars which were not magnetic. Let's call those two groups the magnet-pigeons and the brass-pigeons. In a number of experiments, both groups were taken away from home and let go. On sunny days none of the magnet-pigeons were fooled. They were just as good as the brass-pigeons in starting out in the right direction toward home. How about cloudy, overcast days with no sun? The brass-pigeons chose the right direction. But the magnet-pigeons were in trouble. They started out in different directions and acted completely lost.
为验证这一看法,一组为十只的鸽子背上缚上了强力小磁棒。另一组鸽子则缚着没有磁性的小黄铜棒。我们姑且分别称这两组为磁棒鸽子和铜棒鸽子。在一系列实验中,人们将两组鸽子都带离家门然后放飞。晴天没有一个磁棒组的鸽子上当受骗。它们和那些铜棒组鸽子一样一开始就能选对朝家飞的方向。在没有太阳的多云或乌云密布的日子又会如何呢?铜棒组鸽子选对了方向。但是磁棒组鸽子却陷入了麻烦之中。它们朝不同的方向起飞,完全迷失了方向。
11. What is the easiest way to understand that experiment? Maybe you would like to think about it some more. Here's what the scientists decided after they repeated the experiment many times. When pigeons can see the sun, they use it as their main means of direction finding. When they cannot see the sun, they use some special way to sense direction from the earth's magnetic field.
如何能更容易地理解那项实验的最便捷方法呢?或许你还想进一步思考这一问题。以下就科学家在多次重做那种实验之后做出的判断。鸽子能看到太阳时,它们就用它做为找到方向的主要工具。看不见太阳时,它们会依据地球的磁场采用某种特殊的方法来感知方向。
12. These ideas have been tested further by many different kinds of experiments. One experiment is to put a film of gelatin over a pigeon's eyes to blur its vision. Another is to put a little coil of wire on top of a pigeon's head and use an electric current from a small battery to make an electro-magnet. Enough experiments have been done to decide that homing pigeons (and maybe other birds) seem to have a build-in clock. The big questions is how these work and where they are located in the bird's body.
这些见解已经被不同类的实验进一步验证过。有一项实验是在鸽子的双眼上蒙上一层薄薄的动物胶以模糊其视线。另一项实验是在鸽子的头顶端绕上一个小金属线圈并用一小块电池发出的电流制成的一个电磁体。已做了足够的实验来证明:信鸽(也许还包括其他的鸟类)似乎身上都存在一个内在的时钟。现有的大的问题是:这些钟是如何工作的,它们又会安置在鸟体的什么部位。

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