Recording an earthquake

原文

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 with would stand up 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 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.

But instruments far more deliecate 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 to and fro and around but not up and 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 a 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 ten weight moves but slightly or not at all. 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 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 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.

When the instrument is situated at more than 700 miles from the earthquake centre, the graphic record shows three waves arriving one after 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. The third, or main wave, is the slowest and has travelled round the earth through the surface rocks.

--H.H,SWINNERTON The Earth beneath Us--

译文

地震犹如夜贼，悄然而至，毫无预兆。因此，必须发明一些永不打盹、永不休眠的仪器。有些装置相当简单。例如，有一种装置由各种长短、粗细不同的杆子组成，它们像九柱戏的木瓶一样竖立着。当震动来临时，它会摇晃这些杆子所置放的坚固台面。如果震动较轻，只有那些不稳定的杆子会倒下；如果震动强烈，它们全都倒下。这样，这些杆子通过倒下以及倒下的方向，便为那酣睡的科学家记录下了震动的强度——即使震动微弱到无法将他唤醒——以及震动的来向。

但是，要取得真正的重大进展，就需要比这更精密的仪器。理想的目标是设计出一种能用笔在纸上记录地震通过时地面的运动或台面的运动的仪器。在我写作时，我的笔在移动，而纸却保持静止。无疑，通过练习，我最终能学会在纸张移动时保持笔静止来写作。这听起来是个愚蠢的建议，但这正是某些早期记录地震波的仪器（地震仪）所采用的原理。然而，当台面、笔架和纸张都在移动时，又怎能写出清晰的字迹呢？解决这个问题的关键在于一个日常观察：为什么一个人站在公共汽车或火车上，当车辆突然启动时，会倾向于跌倒？那是因为他的脚在移动，而他的头部却保持静止。一个简单的实验能帮助我们更进一步。将一个重物系在一根长绳子的末端。将手举高在空中，握住绳子，使重物几乎触及地面。现在，将手前后左右移动，但不要上下移动。你会发现，重物几乎不动或只移动很微小。想象一下，地震震动在摇晃地板、纸张、你和你的手。在这一切运动之中，重物和笔会保持静止。但是，随着纸张在笔尖下左右移动，它的运动就会以墨迹记录在纸面上。正是基于这个原理，制作了最初的仪器，但当转鼓在震动时，笔所绘的线条会左右扭动。然而，这种所描述的装置只记录了波动的水平分量，事实上，波动的运动要复杂得多。如果我们能实际看到一个粒子——如岩石中的沙粒——所描绘的路径，它会更像一只蓝蝇在房间里嗡嗡飞舞：上下、前后、左右。人们已经设计出仪器，并能将它们安置好，以便在不同的图表上记录这三种元素。

当仪器位于距地震中心700英里以上时，图形记录显示有三道波依次到达，间隔很短。第一道记录了纵波的到达。第二道标志着横波的到达，这些波传播较慢，比第一道晚几分钟。这两道波都是穿越地球内部传播的。通过研究这些波，人们对地球内部有了如此多的了解。第三道，或称主波，是最慢的，它是绕地球表面岩石传播而至。

--H.H,SWINNERTON The Earth beneath Us--

词汇表

earthquake

名词

英:/ˈɜːθkweɪk/

美:/ˈɝːθkweɪk/

定义

1. 地震 - A sudden violent shaking of the ground caused by movements in the Earth's crust.

例子: The earthquake in 1906 destroyed much of San Francisco.

例子: Scientists study earthquakes to predict future disasters.

近义词

tremor: 通常指较小的地震，强调短暂且不那么破坏性，而 earthquake 更常用于重大事件。

seismic activity: 更正式的术语，指地震相关运动，可能包括多个地震，而 earthquake 具体指单一事件。

quake: 更口语化，常用于非正式描述，与 earthquake 类似但语气较轻。

反义词:

stability, stillness, calm

用法

常用于描述自然灾害的语境中，常见搭配如 'earthquake-prone area'（地震多发地区），在科学或新闻报道中频繁出现。

形式:

复数: earthquakes

关键句型 "If + subject + were + adjective, + main clause"

定义

此句型是一种条件句结构，常用于表达虚拟或假设的情景，尤其是在对现在或未来的情况进行不现实的假设时。基本结构为：If（如果）+ subject（主语）+ were（be动词的虚拟形式）+ adjective（形容词）+ main clause（主句）。例如，文章中的 "If it were gentle, only the more unstable rods fell." 根据《剑桥英语语法》教材，这种句型属于第二类条件句（unreal present conditionals），用于表示与事实相反的假设，were 用于所有主语，以强调虚拟语气。

它帮助表达假设结果，让句子更生动和正式。

用法

此句型主要用于描述假设情景，如科学实验或日常生活中的"如果...会怎样"。规则：在从句中，使用 were 代替 was，即使主语是单数第三人称；主句通常用 would + verb 或简单过去时表示结果。在语法体系中，它属于条件句家族，与第一类条件句（real conditionals，如 "If it rains, I stay home"）形成对比，后者表示真实可能性。

横向比较：与 "If + subject + is + adjective"（真实条件）相比，此句型更强调不现实性，例如 "If it is gentle" 表示实际可能，而 "If it were gentle" 假设一种理想状态。与其他语法点联系，如虚拟语气在礼貌请求中的使用（e.g., "If I were you, I would go"），它能链接到情态动词的学习，帮助学生理解英语中假设与现实的区分。

在文章中，此句型用于解释地震强度，帮助学生看到科学描述中的应用。

注意事项

学生常犯的错误包括：将 were 误用为 was，如 "If it was gentle"，这会让句子失去虚拟语气，显得不正式；另一个问题是主句时态不当，例如用现在时代替过去时或 would。纠正建议：始终记住虚拟语气的固定模式，并通过练习区分真实和虚拟条件。

常见偏误还包括忽略逗号或主句的连接，导致句子不完整。举例：

错误示例：If it was severe, they fall.
正确示例：If it were severe, they all fell.

练习时，注意语调的柔和，以突出假设性。

练习

原创例子：假设你在讨论天气变化，可以说 "If the weather were perfect, we would go hiking." 学生可以替换关键词，如将 "perfect" 换成 "rainy"，变成 "If the weather were rainy, we would stay indoors." 这能帮助学生应用到实际场景，例如在科学实验中说 "If the experiment were successful, we would record the data."

通过这种替换，学生能加深对句型的掌握，并尝试在对话中自然使用。

额外内容

背景知识：虚拟语气起源于古英语，强调礼貌和假设，在现代英语中常用于正式写作或科学描述中。对比分析：与中文的 "如果...就..." 类似，但英语更依赖动词形式（如 were），而中文通过词汇表达。相比法语的条件句，英语的此结构更简单，不需复杂的动词变位。学习此句型能丰富学生的表达，帮助他们在阅读科学文章时更好地理解假设场景，同时扩展到其他虚拟结构如 "I wish it were..."。