1.Have you any empty cups，or jugs，or bottles in your house ？No，not one.You may have many which you call empty，but they are really all full of air.
2.Have you ever noticed how hard it is to fill with water from the tap a bottle which has a narrow neck？The bottle is full of air，and the air must get out of it before the water can get in.Two things cannot be in the same place at the same time.
3.Air and water are both called fluids，because they can flow from one place to another.Wind is nothing but air flowing from one place to another.
4.Air is a gas.When pure，it has no colour，taste，or smell.The air is many miles high.Men have gone seven miles up in a balloon；but even then they were not near the top of the air.
5.But the air does not reach all the way to the sun，moon，and stars.The air lies all round the earth on which we live，and it is of great use to us.
6.The air is of great use in helping things to burn.Let us light two or three bits of candle and put them under glass tumblers of different sizes.Soon all the candles will go out.The candle under the smallest tumbler，which has least air in it，will go out first.
7.It is the air in a room that makes the fire burn brightly.It burns better when you open the door or the window，because you then let in more air.
8.And it is the air that keeps all things alive.All animals and all plants must have plenty of fresh air to breathe，or they will soon die.
9.We must be very careful to let plenty of fresh air into the rooms in which we live.The windows should be left open a little，even at night.
10.Do you want to feel the air？All you need to do is to move your hand about quickly.Or you may squeeze a foot-ball，or a paper bag which you have blown full with your breath.All of these are full of air.
SUMMARY
Air is a gas which，when pure，has no colour，taste，or smell.It lies all round the earth，and is of great use to us.It is called a fluid，because，in the form of wind，it flows from one place to another.Air keeps all things alive.It also makes things burn.Plenty of fresh air should be let into the rooms in which we live.
【中文阅读】
1．小朋友，你家里有空杯子、空水壶、空瓶子吗？没有，一个也没有！可能有不少杯子瓶子，你管它们叫“空的”，可是，它们都盛满了空气！
2．你注意过没有，用水龙头往窄口瓶里面灌水，想把瓶子装满，是一件特别困难的事儿。因为瓶子里充满了空气，只有空气先出来，水才能进去。这两种东西，在同一个时间，同一个地点，是不能待在一块儿的。①3．空气和水都叫流体，因为它们都能从一个地方流到另一个地方。风，就是空气从一个地方流到另一个地方。
4．空气是一种气体，纯净的空气是无色无味的。地球表面的空气，有好多英里厚呢。人类曾经坐气球升到7英里的高度，可是，这个高度离空气的顶端还很远呢！②5．可是，空气并不是一直延伸到太阳、月亮、星星的。空气只在地球周围有一层，空气对我们十分有用。③6．空气可以帮助燃烧。咱们点起两三根蜡烛来，把蜡烛倒扣在大小不同的平底玻璃杯里。很快，蜡烛就都熄灭了。最小的平底杯里面，空气最少，所以这里的蜡烛也就最早熄灭。
7．房间里的空气，让火烧得更旺。你在开门、开窗户的时候，火会烧得更好一些，因为你把更多的空气放进了屋子。④8．所有的生物，也都需要空气才能活。一切动物和植物，都必须有足够的新鲜空气呼吸才行，不然很快就会死掉的。
9．我们一定要小心，要让自己的房间有足够的新鲜空气。就算晚上，也要开一点儿窗户。
10．你想感觉一下空气吗？只要把手很快地摆来摆去就行了。也可以挤一下足球，挤一下吹足了气的纸袋子。这些东西里面，都充满了空气。⑤译注①严格地说，有一点儿空气可以溶解在水里，第7课里提到的金鱼，和其他一切水生动物，也都是靠这点儿空气生存的。但是，大部分空气还是不溶于水，所以水和空气还是要互相挤占地方。
②空气是多种气体混合成的，100份体积的空气，有78份氮气，21份氧气，1份二氧化碳和其他气体。英里是英制尺寸，英国人一直到现在还在用。1英里=1.609公里，7英里高度，也就是大约11.3公里。这里说的事情，指的是1862年英国人詹姆斯·格雷休（James Glaisher）和亨利·考科斯维尔（Henry Coxwell），乘坐煤气气球，升到了11.887公里的高度。最新的载人气球飞行高度纪录，是1961年的34.668公里；无人气球飞行高度纪录，是2002年的53公里！你看，大气层是多么厚啊！
③现在一般认为，大气层的厚度是100公里左右，有11座珠穆朗玛峰叠起来那么高呢！
④这里说的可能主要是炉火。现代居民一般不用明火取暖了，但是，在煤气灶和烧柴的灶上，还可以见到这种现象。
⑤空气没有固定的体积，在压缩之后拥有巨大的能量。压缩空气是仅次于电能的第二大动力能源。最常见的压缩空气待在皮球和轮胎里面，此外，在公交车的车门里，工厂的水压机里、气锤里，煤矿的风镐里，都能找到它。
THE CAT
