Each of us drinks about three pints1 of fresh water every day, and we use a great deal of water for washing, for cooking, and for other purposes. Where does all this water come from? In some places we get water from wells, and in other places from rivers or lakes. But from whatever source we get the water, it is quite certain that at one time or another it must have fallen from the clouds as drops of rain.
我們每個人每一天都會飲用3品脫左右的淡水, 而日常生活中的清洗、烹飪與其他諸多活動都離不開用水。這些水都是從哪里來的呢? 在有些地方, 人們從井中取水, 而在另外一些地方, 人們從河流或湖泊中取水。然而, 無論我們從哪里取水, 可以肯定的是, 天上的云朵時不時就會降下雨水。
Have you ever been in a cloud? Perhaps you have climbed to the top of a high hill, and have seen a white cloud come scurrying2 towards you, till it has covered the hill-top and everything above, below, and around you. The cloud was no longer white, but of a dull grey colour, like the mistwhich we see on a foggy morning. Indeed a fog is simply a cloud resting on the ground.
你看到過云朵嗎? 也許你曾經爬到山峰之上, 看到一塊白云快速朝你飄來, 直到它將山頂與周圍空間中的萬物, 包括你在內, 全部包裹起來。這時, 云朵不再是白色, 它變成了昏暗的灰色, 就像是朦朧的清晨時分天空的那層薄霧。實際上, 霧氣就是落在地面上的云朵。
But what are the clouds made of? They are just like the clouds of white steam, as we call it, that you see rising from a boiling kettle. The white steam and the clouds are both composed of extremely small specks3 of water, so small that they have been called water-dust. When a number of these water-specks join together, they form a drop of rain, and then the weight of this rain-drop makes it come pattering quickly to the earth.
然而, 云朵究竟由什么構成呢? 其實, 它們與那些從沸騰的水壺中冒出的白色水蒸氣一樣。白色蒸汽與云朵均是由很小的水粒構成, 因為它們的體積實在太小, 所以我們稱之為水霧。當許多水粒凝聚在一起時, 它們就變成了雨滴。隨后, 雨滴的重量使得自己迅速落到了地面。
How did all this water which forms the clouds and the rain get into the air? It was evaporated by the heat of the sun from the surface of the oceans and seas, and rivers and lakes. Three-quarters of the surface of the great globe on which we live is covered with water.
這些構成云朵和雨水的水分是怎樣進入到空氣中的呢? 它們由海洋、河流與湖泊表面的水在太陽熱量的作用下蒸發而成。在我們生活的這個巨大星球中, 四分之三的表面都被海水所覆蓋。
Every day the sun's rays change thousands of tons of liquid water into water-vapour; and this water-vapour mingles4 with the air, and is carried along by the wind. While it remains5 in the form of vapour, however, we cannot see it, because it is quite colourless and transparent6.
每天, 太陽光都能夠將數千噸的液態水轉化為水蒸氣；隨后, 水蒸氣與空氣混合在一起并隨風飄動。然而, 只要這些水分保持蒸汽狀態, 我們就無法看到, 因為它是無色透明的。
The air near the surface of the earth is warmer than that which is higher up, so when the water-vapour rises very high above the ground, it is cooled. We have learned that when water-vapour is cooled it is condensed. So the water-vapour is first changed into those very tiny specks of liquid water which have been called water-dust, and appears as clouds; and then these specks of water join together to form drops of rain.
靠近地球表面的空氣溫度比高空的空氣溫度要高一些, 因此, 當水蒸氣漂浮到高空時就會被冷卻。我們知道, 水蒸氣遇冷之后就會產生冷凝。因此, 水蒸氣首先變成了非常細小的水粒——也就是我們所說的水霧——并構成了云朵, 然后這些水?；憔墼諞黃鴣晌擻甑?。
You must at one time or another have tasted drops of rain as they blew against your face, and so you know that the rain-water is fresh water. But the water of the sea, from which that rain-water came, is quite salt. How is it that rain-drops of fresh water can come from the salt sea?
你一定淋過雨而且嘗到過雨水的味道, 因此你知道, 雨水屬于淡水。然而, 雨水來自海水, 而海水中卻含有很多鹽分。那么, 海里的咸水怎么會變成不含鹽的雨水呢?
In last Lesson you were told that salt water can be made fresh by distilling7 it. Now rainwater is really distilled8 water. If you boil salt water in a small saucepan until the water has all passed away as steam, the salt that was dissolved in it will all be left behind as a white crust on the bottom of the saucepan. In exactly the same way the heat of the sun turns the water of the sea into vapour, but not the salt that is dissolved in it. So when this vapour is changed back into water again, it forms pure fresh water.
通過上一課的學習, 你了解到, 咸水可以通過蒸餾而變成淡水。實際上, 雨水是名符其實的蒸餾水。如果你用燉鍋來煮沸咸水, 等到所有的水分都以蒸汽的方式蒸發之后, 咸水中溶解的鹽分就會變成鍋底上一層白色的粉末。太陽的熱量正是通過這種方法將海水變成蒸汽, 而海水中溶解的鹽分則留在了海洋之中。因此, 當水蒸氣再次變成水滴的時候, 淡水應運而生。
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