新概念第四冊課文精講 Lesson42:記錄地震

課文42 記錄地震

792. An earthquake comes like a thief in the night, without warning.

地震就像夜間的小偷，不打招呼就來了。

793. It was necessary, therefore, to invent instruments that neither slumbered nor slept.

因此，有必要發(fā)明一種儀器，既不打盹兒，也不睡覺。

794. Some devices were quite simple.

有些裝置非常簡單。

795. One, for instance, consisted of rods of various lengths and thicknesses with would stand up end like ninepins.

例如，有一種裝置是由一些長短、粗細不同的木棒組成，就像九柱戲的木棒一樣堅立著，

796. When a shock came, it shook the rigid table upon which these stood.

一旦有地震，就會震動豎立在堅硬的桌上的木棒。

797. If it were gentle, only the more unstable rods fell.

如果地震輕微，只有不穩(wěn)定的木棒倒下;

798. If it were severe, they all fell.

如果地震劇烈，所有的木棒都會例下。

799. Thus the rods, by falling, and by the direction in which they fell, recorded for the slumbering scientist the strength of a shock that was too weak to waken him, and the direction from which it came.

由于地震太弱而未驚醒科學家時，木棒倒下的多少和倒下的方向就為科學家記錄下了地震的強度和地震方向。

800. But instruments far more deliecate than that were needed if any really serious advance was to be made.

但是，如果要取得真正重大的進展，需要有比這種裝置精細得多的儀器。

801. The ideal to be aimed at was to devise an instrument that could record with a pen on paper, the movements of the ground or of the table as the quake passed by.

理想的目標是設(shè)計出這樣一種儀器：當?shù)卣鸢l(fā)生時，它能用筆在紙上記錄下大地和桌子運動情況。

802. While I write my pen moves, but the paper keeps still.

我寫字時，筆是移動的，紙是靜止的。

803. With practice, no doubt, I could in time learn to write by holding the pen still while the paper moved.

毫無疑問，經(jīng)過練習，我最終能夠?qū)W會筆不動而紙動來寫字。

804. That sounds a silly suggestion,

這聽起來似乎是一種愚蠢的想法，

805. but that was precisely the idea adopted in some of the early instruments (seismometers) for recording earthquake waves.

但是早期記錄地震波的儀器(地震儀)正是采用了這中思路。

806. But when table, penholder and paper are all moving, how is it possible to write legibly?

可是，當桌子、夾筆裝置、紙都在移動時，怎么能書寫得清楚呢?

807. The key to a solution of that problem lay in an everyday observation.

可以從我們的日常生活觀察中找到這個問題的答案。

808. Why does a person standing in a bus or train tend to fall when a sudden start is made?

一個人站在公共汽車或火車上，當車突然開動時，他為什么會傾倒呢?

809. It is because his feet move on, but his head stays still.

這是因為他的腳動了，而他的頭保持著靜止。

810. A simple experiment will help us a little further.

再做一個簡單的實驗可以幫助我們進一步理解這個問題。

811. Tie a heavy weight at the end of a long piece of string.

把一個重物拴在一根長繩子的一端，

812. With the hand held high in the air, hold the string so that the weight nearly touches the ground.

把手高高舉在空中握住繩子，讓重物幾乎接觸地面。

813. Now move the hand to and fro and around but not up and down.

然后把手前后左右以及旋轉(zhuǎn)擺動，但不要上下擺動。

814. It will be found that the weight moves but slightly or not at all.

結(jié)果會發(fā)現(xiàn)，重物是動了，但動得很小，甚至沒動。

815. Imagine an earthquake shock shaking the floor, the paper, you and your hand.

假定地震發(fā)生了，地板、紙、你和你的手都會動，

816. In the midst of all this movement, the weight and the pen would be still.

在這些所有的運動中，重物和筆卻不動。

817. But as the paper moved from side to side under the pen point, its movement would be recorded in ink upon its surface.

由于紙在筆下來回運動，紙的表面就會用墨水記錄下地板運動的情況。

818. It was upon this principle that the first instruments were made,

根據(jù)這一原理，制造出了最初的地震儀器，

819. but while the drum was being shaken, the line that the pen was drawing wriggled from side to side.

但是紙是卷在慢慢放置的圓筒上的。只要一切都是靜止的，筆就會劃出一條直線;

820. The apparatus thus described,however, records only the horizontal component of the wave movement, which is, in fact, much more complicated.

但是，圓筒受到震動，筆所畫出的線就會就會左右擺動。

821. it would be more like that of a bluebottle path described by a particle,such as a sand grain in the rock,

假如我們真能看到諸如巖石中一個沙粒子的運動軌跡，

822. it would be more like that of a bluebottle buzzing round the room;

那就像一只嗡嗡叫的綠頭蒼蠅在屋內(nèi)飛行的軌跡，

823. it would be up and down, to and fro and from side to side.

呈現(xiàn)出上上下下、來來回回、左左右右3種性質(zhì)的運動。

824. Instruments have been devised and can be so placed that all three elements can be recorded in different graphs.

經(jīng)設(shè)計出了一些儀器，它按照一定的安放方式就可測繪出這三種運動的曲線圖。

825. When the instrument is situated at more than 700 miles from the earthquake centre,

如果把這種儀器安裝在距震源700多英里遠的地方，

826. the graphic record shows three waves arriving one after at short intervals.

曲線記錄就能顯示出前后相同的這3種地震波。

827. The first records the arrival of longitudinal vibrations.

首先記錄下的是縱向波的到達;

828. The second marks the arrival of transverse vibrations which travel more slowly and arrive several minutes after the first.

然后記錄下的是橫向波的到達，橫向波比縱向波傳播得慢，在縱向波到過幾分鐘后能到達。

829. These two have travelled through the earth.

這兩種波都是穿過地球而來的。

830. It was from the study of these that so much was learnt about the interior of the earth.

正是從這兩種波中的研究中，我們可以了解到地球內(nèi)部的許多情況。

831. The third, or main wave, is the slowest and has travelled round the earth through the surface rocks.

第三種波，即主波，是最慢的，是圍繞地球通過表面巖石傳來的。