Heat travels from the sun to the earth by radiation. The rays of the sun must pass through space and the earth’s atmosphere. The heat rays lose very little heat as they go through the atmosphere. When they strike the surface of the earth， the earth absorbs them. The earth becomes heated， and， in turn， heats the air closes to it. When air is next to a warm part of the earth， it expands. Along a lake or ocean on a warm day， the air over the hot land rises. It makes room for the heavy water-cooled air over the ocean， a sea breeze comes in. And the warm air rises， the high cold air is pushed down. In this way winds are set in motion.
Radiation from the sun， changes in temperature and moving air all have a part in causing weather. The amount of moisture in the air also causes different weather conditions. As water evaporates from soil， rivers， lakes， and oceans， it rises and forms clouds. The clouds send down rain and the water cycle begins all over again.
Forces. Even though thunderstorms cause damage at times， they do more good than harm. They bring rain that provides water for all living things. Millions of tons of fertilizer are formed by gases which are formed by the lightning.
Sand and dust storms cause damage to the soil. They carry away soil and even blow crops out of the ground.
Water， plants， ice， and changing temperatures all work together to break up the rocks and the soil. Weathering takes place. Land surface is worn down. This wearing away of soil and rocks is called erosion.
Prediction. The United States Weather Bureau takes recordings of the weather from all parts of the country and even from space by means of satellites. The weathermen find patterns developing. From these patterns they forecast the weather. Some of the instruments they use to predict the weather are thermometers， barometers， weather vanes anemometers， rain gauges， and satellites.
Vocabulary 词汇
atmosphere ["？tm？sfi？] n. 大气、大气层、空气、气氛、环境
temperature ["temp？rit？？] n. 温度、气温、高烧、发热
moisture ["m？ist？？] n. 水分、水气、湿气；
vt. 使防潮
instrument ["instrum？nt] n. 器具、仪器、乐器、傀儡、正式的文件、文书
predict [pri"dikt] vt. & vi. 预言、预测、预示
troposphere ["tr？p？usfi？] n. 对流层
vapor ["veip？] n. 水汽、水蒸气、自夸者；
v. 自夸、（使）蒸发
stratosphere ["str？t？sfi？] n. 平流层、同温层
ultraviolet ["？ltr？"vai？lit] adj. （光）紫外的
mesosphere ["mes？sfi？] n. 中间层
ionosphere [ai"？n？sfi？] n. 电离层
exosphere ["eks？sfi？] n. 外大气层、外逸层
Fahrenheit ["f？r？nhait] n. 华氏温标
altitude ["？ltitju：d] n. 高度、海拔、高处、高地
radiation ["reidi"ei？？n] n. 辐射（能）、放射、放射物
motion ["m？u？？n] vt. （向……）打手势、示意；
n.（物体的）运动、动作、提议
evaporate [i"v？p？reit] vt. & vi. （使某物）蒸发掉；
vi. 消失、不复存在
thunderstorm ["θ？nd？st？：m] n. 雷电交加的暴风雨
fertilizer ["f？：tilaiz？] n. 肥料、化肥
dust [d？st] n. 灰尘、尘土、尘埃、遗骸；
vt. & vi. 拂、掸；
vt. 撒（粉）于
weathering ["wee？ri？] n. 侵蚀、风化
erosion [i"r？u？？n] n. 腐蚀、侵蚀、磨损
forecast ["f？：-kɑ：st] vt. 预言、预报
thermometer [θ？"m？mit？] n. 温度计、体温表
barometer [b？"r？mit？] n. 气压计、晴雨表
vanes [vein] n. 风向标、风信旗、叶、翼
anemometer ["？ni"m？mit？] n. 风速计
gauges [ɡeid？] n. 厚度、直径、测量仪表、规格；
vt. 计量、估计、判断
Practice
I. Complete the following sentences.
1．The air nearest the earth is called the ．
2．The layer of atmosphere above the troposphere is called the ．
3．The layer of gas that helps protect us from the ultraviolet rays of the sun is called ．
4．Heat travels from the sun to the earth by ．
5．Temperature drops about three and one-half degrees Fahrenheit for every thousand feet of ．
6．The wearing away of soil and rocks is called weathering， or ．
7．The United States Weather Bureau weather with the help of instruments．
8．What are four forces that break up rock and soil？
9．What are four instruments that weathermen use to help them predict the weather？
II. Match these items.
1．Thermometer a．moisture in the air
2．-55 degrees F b．wearing away of soil
3．vane c．atmosphere nearest the earth
4．satellite d．man-made object in space
5．altitude e．protects us from sun’s ultraviolet rays
6．barometer f．measures temperature
7．erosion g．temperature 8 to 10 miles above the earth
8．vapor h．measures air pressure
9．troposphere I．height above earth’s surface
10．ozone j．wind direction indicator
译文
地球上所有的生命都取决于大气层。人、动物和植物都像离不开水一样地离不开空气。大气层——这个空气海洋的变化，形成气候。温度变化、气压、空气流动、湿度，所有这些都可以形成气候。通过用特殊仪器研究这些变化，气象员可以预测天气并提前警示我们。
成因。科学家们已经为大气各层命名了：离地球最近的空气层被称为对流层，这层空气包含了大气中几乎所有的空气和大部分水蒸气。大风带、云层和气候，都是对流层中的一部分。
紧接着对流层的是平流层。这层大气从对流层延伸至地球上方约30英里（约48公里）的高度。平流层的上部是所谓的臭氧层，臭氧气体保护人们免受太阳紫外线的照射。
平流层以外，还有三层大气：中间层、电离层和外大气层。在这些层面之外，大气在宇宙中融为一体，那里没有空气存在。
当你往对流层的高处去时，温度会下降。在大约8到10英里的高空，温度会下降到平均华氏-55度。在山上，空气通常会更凉。高度每上升1000英尺（305米），温度大约下降华氏3.5度（2摄氏度）。
热量通过辐射从太阳传递到地球。太阳光线必须通过宇宙空间和地球的大气层，当它们穿过大气层时，损失的热量非常少。当它们到达地球表面时，被地表吸收。于是，地面温度升高，而且反过来使得接近地表的空气也变热。临近地球温暖部分的空气会膨胀，在炎热的日子里，在临近海洋和湖泊的地区，陆地上方的热空气会上升，为海洋上方那些比较重的饱含水分的冷空气提供空间，于是产生了海风。热空气上升，高空冷空气下降，风正是以这种方式开始运动的。
来自太阳的辐射，使温度发生变化、使空气运动，这些都是形成气候的部分原因。空气中水分的含量，也可以产生不同的气候条件。从土壤、河流、湖泊、海洋中蒸发的水分上升并且形成云，云可以形成降雨，于是水循环再次重新开始。
力量。尽管雷暴有时候会造成灾难，但它们仍然是利大于弊。它们带来降雨，为所有的生物提供水。闪电中生成的气体，还可以产生数以百万吨的化肥。
沙尘暴会给土地带来破坏。它们带走土壤，甚至会将作物拔出地面。
水、植物、冰、温度变化，这些因素共同作用，破坏着岩石和土壤。风化产生时，陆地表面会被磨损，这种对土壤和岩石的磨损被称为侵蚀。
预测。美国气象局拥有世界各地，甚至还有通过卫星传回的太空天气记录。气象员从这些记录中寻找气象发展模式，通过这些模式，他们来预报天气。他们用来预测天气的器械包括温度计、气压计、叶轮风速仪、雨量测量器和卫星。
练习
Ⅰ. 完成下列句子。
1．最接近地球的空气被称为 。
2．对流层之上的大气层被称为 。
3．有助于保护我们免受阳光中紫外线照射的空气层被称为 。
4．热量通过 从太阳到达地球。
5． 每增加1000英尺，气温下降约华氏3.5度。
6．土壤和岩石的磨损被称为风化，或 。
7．美国气象局在仪器的帮助下 天气。
8．破坏土壤和岩石的四种力量是什么？
9．气象员使用的帮他们预测天气的四种仪器是什么？
Ⅱ. 搭配下列各项。
1．温度计 a．空气中的水分
2．-55华氏度 b．土壤磨损
3．风向标 c．最接近地球的大气层
4．卫星 d．宇宙空间中的人造物体
5．海拔高度 e．保护我们免受太阳紫外线照射
6．气压计 f．测量温度
7．侵蚀 g．地面上空8至10英里高处的温度
8．水气 h．测量大气压
9．对流层 i．距离地球表面的高度
10．臭氧 j．风向指示器
Ⅰ．1．troposphere 2．stratosphere 3．ozone
4．radiation 5．altitude 6．erosion
7．forecast
8．Water， plants， ice， and changing temperatures．
9．thermometers， barometers， weather vanes anemometers， rain
gauges．
Ⅱ．1．f 2．g 3．j 4．d 5．i 6．h 7．b 8．a 9．c 10．e
07 Gravity 重力是什么
The laws of gravity were discovered by Sir Isaac Newton in 1687. He discovered that the universe was held together and kept in motion by a strange force. This force， called gravity， is a natural force that causes objects to move toward each other. Long before 1687， however， the Bible told those who read it that God holds the world together by His mighty power.
Some things are light in weight. Other things are heavy. A force， called gravity， pulls everything that is on the earth toward the center of the earth. Because of gravity， you have weight. Because of gravity， you can live on a round earth and not fall off.
