记录地震
课文学习台
Recording an Earthquake
区分观点、依据、例子与限制，用自己的话准确重建论述。
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第1段
An earthquake comes like a thief in the night, without warning. It was necessary, therefore, to invent instruments that neither slumbered nor slept. Some devices were quite simple. One, for instance, consisted of rods of various lengths and thicknesses which would stand up on end like ninepins. When a shock came, it shook the rigid table upon which these stood. If it were gentle, only the more unstable rods fell. If it were severe, they all fell. 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.
地震发生时，如同晚上来访的小偷，不会提前告知。因此，有必要发明一种仪器，既不打盹儿，也不睡觉。有些装置非常简单。例如，有一种装置是由一些不同长短和粗细的木棍组成，就像保龄球的九个木瓶一样竖立着。一旦地震发生，竖立着木头的硬桌子便会受到震动。 震动轻微时，只有不太稳的木棍会倒；如果震动剧烈，全都会倒。 于是，木棍的倾倒方向和数量，便可为无法震醒科学家的微弱地震做个记录了，包括强度和方向。
第2段
But instruments far more delicate than that were needed if any really serious advance was to be made. 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. While I write my pen moves, but the paper keeps still. With practice, no doubt, I could in time learn to write by holding the pen still while the paper moved. That sounds a silly suggestion, but that was precisely the idea adopted in some of the early instruments seismometers for recording earthquake waves. But when table, penholder and paper are all moving, how is it possible to write legibly? The key to a solution of that problem lay in an everyday observation. Why does a person standing in a bus or train tend to fall when a sudden start is made? It is because his feet move on, but his head stays still. A simple experiment will help us a little further. Tie a heavy weight at the end of a long piece of string. With the hand held high in the air, hold the string so that the weight nearly touches the ground. Now move the hand to and fro and around but not up and down. It will be found that the weight moves but slightly or not at all. Imagine a pen attached to the weight in such a way that its point rests upon a piece of paper on the floor. Imagine an earthquake shock shaking the floor, the paper, you and your hand. In the midst of all this movement, the weight and the pen would be still. But as the paper moved from side to side under the pen point, its movement would be recorded in ink upon its surface. It was upon this principle that the first instruments were made, but the paper was wrapped round a drum which rotated slowly. As long as all was still, the pen drew a straight line, but while the drum was being shaken, the line that the pen was drawing wriggled from side to side. The apparatus thus described, however, records only the horizontal component of the wave movement, which is, in fact, much more complicated. If we could actually see the path described by a particle, such as a sand grain in the rock, 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. Instruments have been devised and can be so placed that all three elements can be recorded in different graphs.
但是，如果要取得实质的进展，则需要更为精密的仪器。 理想的目标是设计出一种仪器，能在地震发生时，用笔在纸上记录地面或桌子的运动。我写字时，笔动，纸不动。毫无疑问，经过练习，我最终能够学会笔不动而纸动来写字。这想法听起来有点愚蠢，但是早期记录地震波的仪器（测震仪）正是采用了这种思路。可是，当桌子、夹笔装置和纸都在移动时，怎么才能写得清楚呢？这个问题的答案就藏在每天都能观察到的现象之中。站在公共汽车或火车上的人，当车突然启动时，为什么会站不稳呢？这是因为这人的脚跟着车动了，而头没跟着动。一个简单的试验可以帮助我们理解得更为深入。把一个重物拴在一根长绳的一端，把手举高在空中握住绳子，让重物几乎接触着地面。然后把手前、后、左、右，以及旋转摆动，但不要上、下摆动。结果会发现，重物哪怕动了，但动的幅度很小，甚至没动。试想把一支笔拴在重物上，笔尖轻触在地面的一张纸上。 试想地震了，地板、纸、你和你的手都会动， 重物和笔却不动。由于纸在笔下来回运动，纸的表面就会以墨水记录下地板运动的情况。正是根据这一原理，制造出了最初的地震仪器，但是纸是卷在慢慢旋转的圆筒上的。 只要一切都是静止的，笔只会留下一条直线；但是，圆筒受到震动，笔所画出的线就会左右摆动。然而，这里所说的仪器记录下来的只是地震波运动中的水平部分，地震波的实际运动比这要复杂得多。假如我们真能看到粒子的运动轨迹，比如岩石中一个沙粒，就像一只嗡嗡叫的苍蝇在屋内飞行的轨迹，呈现出上上下下、来来回回、左左右右三种性质的运动。仪器被设计出来，并按照一定的方式摆放，这三种运动的曲线图就能被记录下来。
第3段
When the instrument is situated at more than 700 miles from the earthquake centre, the graphic record shows three waves arriving one after the other at short intervals. The first records the arrival of longitudinal vibrations. The second marks the arrival of transverse vibrations which travel more slowly and arrive several minutes after the first. 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.
震源如果距离地震仪700多英里以外，地震仪所录得的地震曲线便会显示出前后间隔很短的三种地震波。纵波的到达首先被记录了下来；横波也紧随其后被记录下来，横波传播较慢，比纵波晚几分钟到达。这两种波都是从地球内部穿越传来的。正是对这两种波的研究，我们得以对地球内部大为了解。第三种波，即主波，最慢，靠围绕地球表层的岩石来传播。
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译文与解析据吴应时整理资料及本站首轮审校稿；词伙与练习提示为本站学习设计。原PDF第184—190页，2022年2月第2版。