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

to and fro ^{if sb. or sth. moves to and fro, they move in one direction and then back again 来 来回回地}

• The swing rocked to and fro.
• I was disturbed by all the people walking to and fro outside the office.
• The boat rocked to and fro on the choppy water.^{船在波涛汹涌的水面上来回摇晃。}

up and down  ^{if sth. moves up and down, it moves towards a higher position and then back to a lower position 上上下下地}

• The boat was moving up and down on the sea.
• The earth trembled and the house seemed to be moving up and down. 
• The crane can move forward and backward, but not up and down.^{起重机可以向前和向后移动，但不能上下移动。}

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

moves slightly ^稍微一动

• The needle on the gauge moved but slightly, indicating a minor change.^{仪表上的指针只移动了一点点，表明变化很小。}
• You can easily see all their bones' shapes as long as they move slightly! ^{肩部的骨头，只要稍稍一动就可以看到所有的骨头形状！}
  

Imagine a pen attached to the weight in such a way that its point rests upon a piece of paper on the floor.

Imagine ^{v.想象，设想}

• Imagine their dismay when they found a beautifully-cooked wallet and notes turned to ash! 
• Imagine loving your enemy and doing good to those who hated you. ^{想像着爱你的敌人，为仇人做好事。}
• One can imagine how regretful he was. ^{可以想像他是多么懊悔。}

be attached to … ^{1. 与…连在一起}

• Lined up against the wall, there were long thin wires attached to metal spheres.
• The warning label was securely attached to the product.^{警告标签牢固地连接到产品上。}
• A trailer was attached to the rear of the truck. ^{卡车后面挂了一辆拖车。}

be attached to … ^{2. 依恋…}

• She was sentimentally attached to this house, for even though it was far too big for her needs, she persisted in living there long after her husband's death.
• She is very attached to her family and friends. ^{她非常喜欢她的家人和朋友。}
• I've never seen two people so attached to each other. ^{我从未见过两个人如此形影不离。}

rest on / upon ^{sth. 1. 靠在…上面}

• She stood three feet high and her hands rested on her hip.
• The weary traveler finally allowed his head to rest upon the soft pillow.^{疲惫的旅行者终于允许他的头停留在柔软的枕头上。}

rest on / upon sth. ^{2. 基于…}

• His fame rests more on his plays than on his novels.
• Does the economy rest on too narrow a base? ^{这种经济的基础是否过于狭窄？}

in such a way that... ^{以至于…的方式}

• She arranged the lights in such a way that they highlighted the painting perfectly.^{她以至于它们完美地突显出画作的方式布置了灯光。}
• And in such a way that it became a weapon in the cold war. ^{这样一来，它会变成冷战中的一件武器。}
• The world has been shaped by technology in such a way that it is no longer surprising. ^{世界已经被技术用这样一种方式定型了，这已经没什么好惊讶的了。}

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

imagine sb. doing sth. ^{想象某人正在做某事}

• I can easily imagine him becoming a successful entrepreneur in the future. ^{我完全可以想象到他未来成为一名成功企业家的样子。}
• She could imagine dark-robed figures moving silently along the stone corridors.
• Imagine you and me going to outer space. ^{设想一下你和我将去到外太空。}

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

in the midst of … ^{1. while sth. is happening or being done 在…发生期间}

• a country in the midst of a recession
• She discovered it in the midst of sorting out her father's things.
• She alone remained calm in the midst of all the confusion.

in the midst of … ^{2. in the middle of a place or a group of things or people 在…之间(地点)}

• I suddenly realized I was standing in the midst of the crowd, but I couldn't see my friends anywhere. ^{我突然意识到自己正站在人群之中，却到处也看不到我的朋友。}
• He described it as 'a very agreeable situation located within two small hills in the midst of which flowed a great river'.
• The small cottage sat peacefully in the midst of a dense pine forest. ^{那座小木屋静静地坐落在茂密的松树林之中。}
• In the midst of the chaos, she remained surprisingly calm.^{在混乱之中，她出奇地保持着冷静。}

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

in ink ^{用墨水写(钢笔)}

• Please write in ink, not in pencil.
• The data from the sensor would be recorded in ink upon the chart.^{来自传感器的数据会以墨水的形式被记录在图表上。}
• The letter was written in ink. ^{这封信是用钢笔写的。}

It was upon this principle that the first instruments were made, but the paper was wrapped round a drum which rotated slowly.

on / upon … principle ^{依照…理论或原则}

• The country is run on socialist principles.
• The project worked on the principle that each person's experience was equally valuable.
• It was upon this principle that the new engine was designed.^{正是基于这个原理，新引擎被设计了出来。}

in principle ^{1. 原则上（但尚未考虑细节）}

• Politicians agree, in principle, so America and the EU have been trying to reach a deal which would eliminate the need to double-test many products.
• In principle, this makes sense. ^{原则上讲得通。}
• Is there a difference in principle? ^{有没有原则上的区别呢？}

in principle ^{2. 理论上（但尚未发生）}

• In principle, the new software should make the accounting system a lot simpler.
• Even assuming this to be in principle possible, it will not be achieved soon. 
• In principle, it should not be too hard. ^{原理上，这应该不会太难。}

wrap sth. round / around sb. / sth.  ^{将某物缠绕/包裹在某人或某物上}

• Ella wrapped a thick coat around her shoulders.
• He wrapped a bandage around my injured wrist.
• She wrapped a warm scarf around her neck before heading out into the snow. ^{出门踏入雪地前，她把一条暖和的围巾围在脖子上。}

drum ^{n. sth. that looks like a drum, esp. part of a machine 鼓状物，鼓状零件}

• The mixture flows to a revolving drum where the water is filtered out. 混合剂流过旋转着的滚筒时水分便从中滤出。
• The oil drum leaks. ^{油桶漏了。}
• Drum brake with large clearance between the feet or oil. ^{制动蹄与制动鼓之间的间隙过大或蹄油。}
• The electrical cable was neatly wrapped round a drum before shipping.电缆在运输前被整齐地缠绕在一个鼓筒周围。

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.

as long as ^{在…的时候，只要…就}

• As long as you're happy, that's all that matters. ^{只要你幸福，这就是最重要的事情。}
• As long as all was still with the patient, the doctor decided to wait.^{只要病人的情况一切保持静止，医生决定等待。}
• As long as you have your health, nothing else matters. ^{只要身体健康，其他任何事都无关紧要。}

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

apparatus ^{n. [U] = equipment 仪器，设备}

• With experience, and with improved apparatus, it is now possible not only to locate a shoal but to tell if it is herring, cod, or other well-known fish, by the pattern of its echo.
• His telescopic observations are justly immortal; they aroused great interest at the time, they had important theoretical consequences, and they provided a striking demonstration of the potentialities hidden in instruments and apparatus.

thus ^{adv. in this way, like this 以此方式，如此，这样}

• calculate the area of the triangle thus formed ^{计算这样形成的三角形的面积}
• Hold the wheel in both hands, thus. ^{用双手握住方向盘，像这样。}
• The process thus described requires specialized tools.^{如此描述的过程需要专门的工具。}

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.

path ^{n. line along which sb./sth. moves （人或事物移动的）路线，轨道}

• the moon's path round the earth
• the path of a tornado
• Scientists used advanced imaging to trace the path described by a photon.^{科学家们使用先进的成像技术来追踪一个光子所描述的路径。}

grain ^{n. [C] a single very small piece of a substance such as sand or salt 小颗粒}

• The recipe only calls for a grain of salt to enhance the flavor of the chocolate. ^{食谱只需要一粒盐来提升巧克力的风味。}
• Even a grain of sand in your eye can cause significant discomfort. ^{哪怕是一粒沙子进到眼里，也会让你感到非常不适。}
• There wasn't a grain of sugar left in the jar after she finished baking the cake. ^{她做完蛋糕后，罐子里连一粒糖都不剩了。}

bluebottle ^{n. large buzzing fly with a blue body 青蝇}

• We could see a bluebottle on the rock. ^{我们能看见一只绿头苍蝇在岩石上。}
• A bluebottle buzzed around the garbage bin. ^{一只蓝蝇在垃圾桶周围嗡嗡作响。}
• The picnic was ruined by the presence of several bluebottles. ^{几只蓝蝇的出现毁了这次野餐。}

buzz ^{v. to make a continuous sound, like the sound of a bee 发出嗡嗡声}

• The city has a real buzz. ^{这个城市真热闹。}
• A low buzz of admiration swept through the assemblage. ^{一阵表示敬佩的低沉的赞赏声在聚集的人群中传开。}
• A buzz of excitement filled the courtroom as the defendant was led in. ^{被告被带进来时，法庭内充满激动的嘈杂声。}

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

element ^{n. one part or feature of a whole system, plan, piece of work etc., esp. one that is basic or important 要素，重要部分}

• Honesty is a vital element of her success.
• Besides ability, the other essential element in political success is luck.
• There is an element of subjectivity in her criticism. ^{她的批评有主观因素。}

graph ^{n. a picture that uses lines or curves to show the relationship between numbers or measurements that change 图，图表，曲线图}

• A bar graph will show you the busy and quiet times during the week. ^{柱状图会显示一周中繁忙和平静的时间段。}
• I first saw a graph similar to this one in a software magazine article. ^{我在一篇软件杂志的文章中第一次看到与此类似的图。}
• We plotted about eight points on the graph. ^{我们在图表上绘出了大约有八个点的曲线。}