歌词
Lesson 42
第42课
Recording an earthquake
记录地震
What does a pen have to do to record on paper the vibrations generated by an earthquake?
在纸上记录地震所引起的震动时，钢笔需要做什么？
An earthquake comes like a thief in the night, without warning.
地震就像夜间的小偷，不打招呼就来了。
It was necessary, therefore, to invent instruments that neither slumbered nor slept.
因此，有必要发明一种仪器，既不打盹，也不睡觉。
Some devices were quite simple.
有些装置非常简单。
One, for instance, consisted of rods of various lengths and thicknesses which would stand up on end like ninepins.
例如，有一种装置是由一些长短、粗细不同的木棒组成，就像九柱戏的木棒一样竖立着。
When a shock came, it shook the rigid table upon which these stood.
一旦有地震，就会震动竖立在坚硬桌子上的木棒。
If it were gentle, only the more unstable rods fell.
如果地震轻微，只有不稳定的木棒倒下。
If it were severe, they all fell.
如果地震剧烈，所有的木棒都会倒下。
Thus the rods, by falling, and by the direction in which they fell,
因此，通过其倒下的方向，
recorded for the slumbering scientist the strength of a shock that was too weak to waken him,
在地震的强度太弱不足以惊醒熟睡中的科学家的时候，
and the direction from which it came.
这些木棒记录了地震发生的方向。
But instruments far more delicate than that were needed if any really serious advance was to be made.
但是，如果要取得真正的重大进展，需要比这种装置精细得多的仪器。
The ideal to be aimed at was to devise an instrument that could record with a pen on paper,
理想的目标是设计出这样一种仪器：
the movements of the ground or of the table as the quake passed by.
当地震发生时，它能用笔在纸上记录下大地和桌子的运动情况。
While I write my pen moves, but the paper keeps still.
当我写字时，笔是移动的，纸是静止的。
With practice, no doubt, I could in time learn to write by holding the pen still while the paper moved.
毫无疑问，通过训练，我最终能学会在笔不动而纸移动的情况下写字。
That sounds a silly suggestion,
这听起来似乎是一种愚蠢的想法，
but that was precisely the idea adopted in some of the early instruments (seismometers) for recording earthquake waves.
但是早期记录地震波的仪器（测震仪）正是采用了这种思路。
But when table, penholder and paper are all moving, how is it possible to write legibly?
可是，当桌子、笔杆、纸都在移动时，怎么能书写的清楚呢？
The key to a solution of that problem lay in an everyday observation.
可以从我们的日常生活观察中找到这个问题的答案。
Why does a person standing in a bus or train tend to fall when a sudden start is made?
当车突然开动时，站在公共汽车或火车上的人为什么会有要摔倒的倾向呢？
It is because his feet move on, but his head stays still.
这是因为他的脚动了，而他的头保持着静止。
A simple experiment will help us a little further.
一个简单的实验可以帮助我们进一步理解这个问题。
Tie a heavy weight at the end of a long piece of string.
把一个重物拴在一根长绳子的一端，
With the hand held high in the air, hold the string so that the weight nearly touches the ground.
把手高举在空中握住绳子，使重物几乎接触地面。
Now move the hand to and fro and around but not up and down.
现在把手来回以及旋转摆动，但不要上下摆动，
It will be found that the weight moves but slightly or not at all.
结果会发现，重物运动的幅度很小，甚至根本没动。
Imagine a pen attached to the weight in such a way that its point rests upon a piece of paper on the floor.
假定按照这样一种方式把笔拴在重物上，使笔尖悬停在地板上一张纸上方。
Imagine an earthquake shock shaking the floor, the paper, you and your hand.
假定地震发生了，地板、纸、你和你的手都会发生震动，
In the midst of all this movement, the weight and the pen would be still.
在这些运动发生时，重物和笔保持静止。
But as the paper moved from side to side under the pen point, its movement would be recorded in ink upon its surface.
但是由于笔尖下方的纸张作往复运动，其运动情况就会被墨水记录在纸张上。
It was upon this principle that the first instruments were made, but the paper was wrapped round a drum which rotated slowly.
根据这一原理，制造出了最初的地震仪器，但是纸张是卷在缓慢旋转的圆筒上的。
As long as all was still, the pen drew a straight line,
只要一切都是静止的，笔就会画一条直线；
but while the drum was being shaken, the line that the pen was drawing wriggled from side to side.
但是当圆筒受到震动时，笔所画出来的线就会左右摆动。
The apparatus thus described, however,
然而，这里所描述的这种仪器，
records only the horizontal component of the wave movement, which is, in fact, much more complicated.
记录下来的只是地震波的水平分量，地震波的运动实际比这要复杂得多。
If we could actually see the path described by a particle,
假如我们真能看到所描述的一个粒子的运动轨迹，
such as a sand grain in the rock,
比方说岩石中的沙粒，
it would be more like that of a bluebottle buzzing round the room; it would be up and down, to and fro and from side to side.
其运动轨迹就像一只嗡嗡叫的绿头苍蝇在屋内的飞行轨迹，呈现出上上下下、来来回回、左左右右三种运动形式。
Instruments have been devised and can be so placed that all three elements can be recorded in different graphs.
已经设计出了一些仪器，把它们按照一定的方式安放就可以记录下这三种运动形式的曲线图。
When the instrument is situated at more than 700 miles from the earthquake centre,
如果把这种仪器安放在距离震中700多英里远的地方，
the graphic record shows three waves arriving one after the other at short intervals.
其记录的曲线表明，这三种形式的波会在比较短的时间间隔内先后到达。
The first records the arrival of longitudinal vibrations.
首先记录下来的纵向波的到达。
The second marks the arrival of transverse vibrations which travel more slowly and arrive several minutes after the first.
然后记录下来的是横向波的达到，横向波比纵向波传播得慢，在纵向波到达几分钟后才能到达。
These two have travelled through the earth.It was from the study of these that so much was learnt about the interior of the earth.The third,or main wave is the slowest and has travelled round the earth through the surface rocks.
这两种波都是穿过地球而来的。
专辑信息