作者：（美）文森特·默奇
出版社：天津人民出版社
格式: AZW3, DOCX, EPUB, MOBI, PDF, TXT
科学读本（英文原版）（第3册）试读：
Lesson 01 Water—Its Properties
“We have not learned all about water yet, it seems,” said Will, as the two boys trudged home from school.
“No,” said Fred, “I expect there is plenty more for us to learn, and yet it all seems so simple when teacher leads us to look at the things in the proper way.”
They had just been promoted again to a higher class, and that day the teacher had given the class the first object lesson of the new course. It was about the properties of water.
Our two boys seemed to have taken a new interest in life and in the things around them from the day they had their first object lesson. They had been through two courses of lessons, and were now about to commence the third.
“What are you so busy with, boys？” said Norah to them after tea.
“We are getting a few things ready for another chat about water,” said Fred, “if you would like to join us, Norah.”
“Oh yes,” said she, “I should. But I can’t think what else you can have to say about water. We know that it is a liquid, and that it dissolves things that are put into it, and that—”
“There, there, wait a minute, little girl,” said Will.“Suppose you tell us why you call water a liquid.”
“Oh, that’s easy,” said Norah. “First of all water has no shape of its own. It always takes the shape of the vessel which holds it. Then, too, it cannot stand in a heap, but always keeps a level surface.
“We cannot grasp water in our hands, to pick up a handful of it, as we could a handful of sugar or flour or raisins. The water would fall away in drops out of our hands and run along the floor, because water always flows down and tries to get lower. Everything that is like water in these respects is a liquid.”
“I think she knows why water is called a liquid,Fred, so we may as well talk now about the other properties of water.” said Will.
Fred had got several tumblers, just as he had seen his teacher do in class. He put clear water in one, and milk in another, and in the rest of them some water that he had colored with a few drops of red, black, and blue ink. He showed Norah these colored waters first, then the milk, and lastly the glass of clear water.
“Now, little girl,” said he, “what color is water？You see it is not white; the milk is white. Neither is it black, or red, or blue.”
“I don’t think it has any color.” said Norah.
“And you are quite right,” said both the boys.“Water is a colorless liquid.”
“Now,” Fred continued, “look through the tumbler of water, and then through the milk. Can you see this ball through the milk？”
“No.”
“Can you see it through the water？”
“Yes, I can see it through the water, but not through the milk.”
“Remember, then, that water is transparent, milk is opaque. Water is a colorless transparent liquid.Milk is a white opaque liquid.”
“And remember, Norah,” said Will, “that we learn these properties of water through our eyes, by the sense of sight.
“Now, suppose we made you shut your eyes,and tell the names of various liquids, such as tea,vinegar, cocoa, coffee, brine, by smelling and tasting them, could you do it？”
“Oh yes, I am sure I could.” said Norah.
“Then shut your eyes, and tell us the name of this one by first smelling it and then tasting it.” said Fred.
“I can neither smell nor taste anything.” said Norah.
“Now open your eyes and see what the liquid is,” said her brother. “You see it is water. Water has neither odor nor taste. We say it is an inodorous and tasteless liquid, but we learn this through two other senses—the sense of smell and the sense of taste.”SUMMARYWater is a liquid. Liquids have no shape of their own; they take the shape of the vessel which holds them; they flow about;they break up into drops; they will not stand in a heap, but always keep a level surface. Water is a transparent, colorless,tasteless, inodorous liquid.
Lesson 02 Some of the Uses of Water
“Now that we know something of the properties of water,” said Fred, “we can talk about a few of the uses to which it is put. What do you think is the most important use which we make of water,Norah？”
“I should say,” replied Norah, “that its chief use is for drinking purposes.”
“Quite right,” said Fred. “We could not live long without drink of some sort, and although we do not always drink water, yet all drinks are made of water.”
“Yes,” added Willie, “and animals and plants, as well as ourselves, require water or they would die.
“We must not forget, too, that our food has to be cooked and prepared with water.
“Then think of the great use we make of water in washing ourselves and our dirty clothes, and in cleaning our houses. Teacher says it is the natural cleanser. We cannot be healthy and happy unless we are clean. Dirt brings disease, and the worst enemy of dirt is water.”
“Now, I want you,” said Fred, “to imagine what would happen if the water, instead of being colorless,tasteless, and odorless, had a taste, smell, and color of its own.
“Picture to yourself our shirts and collars, everything we wear, as well as our floors and tables, and every article of our food, colored red or blue, through being washed or prepared in red or blue water.
“Think of the taste of our food too. It would take the same flavor and the same smell as the water in which it was cooked.
“Water is useful for all these purposes simply because it is colorless, tasteless, and odorless.”
“I have just been thinking,” said Willie, “of what teacher told us about the water cisterns. You know water is very absorbent, and will suck up and hold gases.
“Teacher told us that all rotting or decaying matter in dustheaps and manure heaps gives off bad gases.These bad gases would be sure to find their way into any water that was near, and we could not drink such water without being made very ill.
“The cistern which holds the water for drinking and cooking our food should be kept as far as possible from rubbish and manure heaps, and bad smells of all kinds.”
“There is one great use of water,” said Fred, “that depends upon its being absorbent. Just think of the fishes and other animals that live entirely in the water. These animals all require air. Without air they would die.”
“But how can they get air in the water, Fred？”said Norah. “Do they come up to the top every time they want to breathe？”
“No,” said Fred, “they do not. Many of these creatures never come to the surface of the water at all. Yet they breathe freely, because there is plenty of air in the water.
“The water is absorbent. It is constantly sucking in air all over its surface. It is this air which the fishes and other creatures breathe.”SUMMARYWater is the natural drink of man and all animals. It is the natural cleanser. We cook and prepare our food with water.Water absorbs gases. Fishes can breathe in water, because it contains air. Drinking water should be kept from bad smells of all kinds.
Lesson 03 Birds and their Covering
“We have not had a chat about animals for a long time,” said Fred. “Would you like us to start one this evening, Norah？We had a good lesson on birds today, and I think Will and I can tell you something about it.”
“Oh,” said Norah, “I should like it very much.”
“Well then, you remember we talked about several animals last year,” Fred began. “We had amongst others the cat, dog, sheep, pig, horse, cow,and rabbit. Now think of them, one by one. What sort of clothing have they？”
“They all have different sorts of coverings,” said Norah.
“Quite true,” said Fred. “But all birds are clothed with feathers.
“Now I want you to think of something else.How do all those animals feed their young ones？”
“They nurse them,” said Norah. “I have seen our Tabby nurse her kittens.”
“Did you ever see a bird nurse its young？”
“No, the parent birds feed their little ones with bits of food which they find for them. Birds do not nurse their young.”
“There is just one other point for us to notice now about birds,” Fred continued. “All the animals we have mentioned live and move about either on the earth or under it. But what can you tell me about birds？”
“Birds fly in the air,” said Norah. “They have wings.”
“Quite right,” said both boys. “Now, Norah, you know the three chief things about birds. Birds are the only creatures that are clothed in feathers. Birds do not nurse their young. Birds have wings and fly in the air.”
“But let us fix our attention now,” said Fred once more, “on the covering of feathers. This is the warmest,lightest, and, at the same time, the most beautiful of all coverings.
“Wait a minute while I go to the pigeon-house and get my little pouter. He is very tame, and will perch on my arm while we talk about his feathers.”
Fred was back again in no time with his pigeon,and then he began. “Suppose we look first at the wings and tail. Notice these long feathers, as I spread out the wing. They have a stem, which we call the quill. These are the quill feathers. They are fixed into the skin of the bird by a sort of root. The bird makes use of these long feathers in the wings and tail for flying.
“Now, if you run your finger over the birds body,you will find that the whole of the body is covered with smaller feathers, which form its real covering.These are the clothing feathers.
“Notice that when I run my fingers over them the wrong way, I ruffle them up; but they can be easily smoothed back again into their proper position, and then they are seen to be beautifully arranged, one overlapping the other, so as to form a close-fitting coat.
“Such a coat of feathers closely overlapping one another is of course very warm. But some birds,such as ducks and geese and swans, that spend much of their time in the water, both in winter and summer, are still further protected from cold. They have a close-fitting under-jacket of very small, fine,soft, fluffy feathers, which we call down.”
“Yes,” said Norah, “I have seen the down on the geese at Christmas time, and how tiresome it is to pick it all off clean.”SUMMARYBirds are clothed with feathers. They do not nurse their young. They have wings, and fly in the air. Birds have large quill feathers in the wings and tail, and clothing feathers to cover the body. Some birds have soft down under-jackets.
Lesson 04 A Feather
“Where have you been, Fred？” asked Will. “We have hunted everywhere for you.”
“I’ve been in the fowls’ house,” said Fred, “to find a few feathers. Look what a fine lot I’ve got. They will do well, won’t they？”
“Oh, I know,” said Will. “You are thinking about our lesson. Yes, they will be just the thing. Where’s Norah？”
In a few minutes the three were seated at the table ready for a chat, and Fred handed some of the quill feathers round.
“Now, a glance at one of these feathers,”he said, “will tell us that it consists of two parts. There is the long stem, which runs from the root to the very tip of the feather,and on either side of this is the blade or web.
“Let us examine the central stem first. The lower half of it near the root seems to be quite different from the upper half. Try and cut it across with your knife, Will.” Will tried, but he found it no easy task to cut through this part of the stem, for it was like strong, tough horn. However, he did cut it across at last, and then they saw that it was really a round hollow tube.
“Teacher calls this lower part of the stem the quill,” said Fred. “ It is thin, hollow, and extremely light, but it is very tough, strong, and elastic, and will bear a great deal of rough usage. The lower end of it forms the root, which holds it in the skin of the bird.
“Now let us look at the other part of the stem. It is called the shaft. Suppose you strip your feather and then examine it. What can you say about it？”
“The quill of the feather is round,” said Norah,“but this part has four sides. The upper and under sides are smooth, like the surface of the quill, the other two sides are rough. It was from these edges of the shaft that we tore off the web just now. I can see, too, that the shaft becomes smaller and smaller towards the tip.”
“Quite right,” said Fred. “Now we will go a step farther. Watch, while I cut through the shaft as we did through the quill just now. This part of the stem, you see, is not hollow like the quill. It is filled with a loose, white, tough substance—the pith.
“We have done with the quill and the shaft now,”he continued. “I want you to turn your attention to the other part of the feather, which teacher calls the web.
“If you examine this web you will see that it is made of a great many long, narrow, thin blades—the barbs. These spring from the shaft, and are arranged with their two flat sides close together.
“Pluck one or two of them. You can see that the edges of the barbs are provided with a great number of very small blades—the barbules. Barbule means a little barb.
“These barbules are really little hooks. They interlock themselves one in the other, and so hold the barbs of the web close together.
“Look, while I run my finger along the feather the wrong way. You see the little hooks are pulled apart, and the barbs themselves are separated from each other.
“Teacher showed us that the barbs always point towards the tip of the feather, and away from the quill ; and, in addition to that, every feather on the bird’s body points backwards.
“This is very important. As the bird moves through the air the feathers are pressed closer and closer to its body. This helps the bird in its flight,and, at the same time, keeps it warm.”SUMMARYA feather consists of a stem and a web. The stem has a hollow quill, and a shaft filled with light pith. The web consists of barbs; the edges of the barbs are held together by the barbules. All the birds’ feathers point backwards.
Lesson 05 The Uses of Feathers
“You have not forgotten our chat about feathers,Norah？” said Fred a few evenings later.
“Oh no,” said his sister. “I know the three kinds of feathers which birds have—the quill feathers of the wings and tail, the body or clothing feathers,and the under-jacket of down.”
“Teacher has been showing us that all these are very useful to us in their own way. Shall I see what I can remember of our lesson？”
“Oh yes, do, Fred, please,” said Norah.
“Well then, let us begin with the quill feathers.These are mostly used for adorning ladies’ hats and bonnets. The most beautiful and costly feathers are the wing feathers of the ostrich, a great bird ever so much bigger than a man.
“In Africa there are large ostrich farms, where these birds are reared solely for their feathers, and I am sorry to have to say, Norah, that the cruel people of those farms pluck the feathers at regular seasons from the poor birds while they are alive.
“I suppose very few of the ladies who wear the beautiful feathers have any idea of the torture the poor birds suffer to provide for their dress. It always makes me very angry when I think about it.”
“It’s just as cruel to slaughter other birds,” said Willie, “by thousands, as they do, for nothing else but their beautiful feathers. Of course it is always the most beautiful of the birds that they choose. If I were a lady I would never wear one of the dreadful feathers.”
“I’m sure I never will,” said Norah, with a shudder. “How cruel it is!”
“Teacher showed us some quill pens,” said Fred.“They are made of the wing feathers of the goose and swan. We rarely see quill pens now. They are not so much used as they once were. Nearly every one writes now with a steel pen. But the quill pen is still used for certain purposes, and a small pen made of the crow quill is the best for some kinds of drawing.”
“The clothing or body feathers of birds are very largely used for stuffing beds, pillows, and cushions.The birds which supply most of the feathers for this purpose are the poultry birds and wild fowl. They are killed for food, and the feathers are plucked from their dead bodies.”
“I was thinking,” said Norah, “of the great number of these birds we see in the shops about Christmas time. What an immense quantity of feathers there must be.”
“Yes,” said Fred, “and teacher says that, besides these, we bring in year after year shiploads of feathers from other countries.”
“Very little trouble is wanted to prepare them for use. All that is needed is to dry and beat them to remove dust, and then to bake them in an oven to kill the vermin in them.”
“Do you remember what teacher said about the eider down, Fred？” asked Will. “The down is got from the eider duck, Norah, a wild seabird that makes her nest on the rocks by the sea, and lines it with down from her own breast. In this nest she lays her eggs.
“Each day men go round and take away some of the down and some of the eggs. Each day the bird plucks more down from her breast and lays another egg, only to have the nest robbed again and again,till she has no more down to spare.
“This may seem cruel, but the bird is not fit for food, and as we want the down, it is better than slaughtering the birds to get it.”SUMMARYThe quill feathers of some birds are used for ladies’ hats and bonnets, for ornaments, and for making pens; the clothing feathers and down for stuffing beds, pillows, cushions, etc.
Lesson 06 Water as a Solvent
“I suppose,” said Willie, “teacher only wanted to find out today how much we remember of our early lessons. He went over all the old work.”
“Yes,” said Fred, “and as soon as tea is over I am going to try Norah. I wonder whether she has forgotten all about it.”
As soon as they were free, therefore, the boys got a few things together, and Fred began just as their teacher had begun in class.
“Look, Norah,” he said, “I have here a piece of coal and a piece of salt. If I put them into water can you tell me how they will act？”
“Oh yes,” said Norah. “The salt will dissolve in the water, but the coal will not dissolve.”
“But what do you mean by the word dissolve？” he asked again.
“The word dissolve means to loosen or separate,”replied Norah. “The water has the power to loosen and break up, or separate the solid salt into such tiny little particles that we cannot see them. When it is broken up into these tiny particles, we say the salt is dissolved. The water cannot break up the coal. It will not dissolve.”
“Do you know what we say about the salt because we can dissolve it in water, Norah？”
“We say,” replied Norah, “that the salt is soluble.The coal is insoluble; that means not soluble.”
“What other substances will dissolve if we put them in water？”
“Sugar, soda, alum, and lime all dissolve. They are all soluble substances,” said Norah.
“Now tell us what we say about the water that dissolves these things？” said Fred.
“We say that water is a solvent for sugar, salt,alum, lime, and any of the things which it dissolves,”said his sister.
“See,” Fred continued, “I can take the coal out of the water just as it was when I put it in. But can I take the salt out in the same way？”
“No, the salt cannot be taken out, because it is broken up into very small particles, and the particles are scattered through the water.”
“Could I get the salt out of the water in any other way？” asked Fred.
“If you boiled the water,” said Norah, “it would all pass away as steam, and the salt would be left behind.”
“Do you remember,” Fred asked again, “that we once filled a tumbler with water to the brim, and then put in salt, a spoonful at a time？”
“Oh yes,” said Norah, “and I thought you were so clever. I could not make out how you were able to put all that salt in without spilling any of the water.”
“But you know now, Norah, don’t you？” asked Will.
“Yes,” said Norah, “you told me all about it. The water is porous and absorbs the tiny little particles of salt into its pores.”
“That’s right,” said Fred. “The tiny dissolved particles, after being broken up and scattered in all directions, fill up the pores in the water. When the pores are all filled the water can hold no more, and the rest of the salt falls in a solid wet mass to the bottom. Remember that water absorbs air and gases in the same way by sucking them up into its pores.”SUMMARYWater loosens or breaks up salt and other substances into tiny particles too small to be seen. It dissolves them. The dissolved particles are absorbed into the pores of the water. We can get rid of them only by boiling the water. Water will not dissolve some substances. They are insoluble.
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