Maps. — Sign pictures such as the one of the land of the Tigris and Euphrates in Figure 35 are called maps. Maps are useful guides for travelers who know how to read the signs on them. Suppose your next journey is by sea from Basra to a land far to the west of it. The first part of this journey would be down the Shat-el-Arab to the Persian Gulf. From Figure 35, find in what direction you would be going during this part of the journey.

Before you can find in what directions you would sail during the remainder of the journey, several things must be added to the map in Figure 35. Suppose you had airplane views which helped you make a map of the sea coasts in the region southeast of the land of the Tigris and Euphrates. If you added such a map to the one in Figure 35, you then would have ‘a map like the one in Figure 37.

A narrow place in the sea connects the Persian Gulf with the great sea southeast of it. Find in Figure 37 this narrow place in the sea. Compare the length of the Persian Gulf with the distance between Basra and Bagdad.

After looking at Figure 37, do you not wonder if the great sea southeast of the Persian Gulf joins the seas west of the Tigris and Euphrates region? After another part of the map is added, you can find out whether it does or not. Do you see now some ways in whith maps will be helpful in your journeys?

A sign for the whole world. — Before you read about other journeys, it also will be helpful if you think about a sign that stands for the whole world. Then, as you continue your journeys, you can see where the signs or maps of the lands in which you travel belong on the world sign. Since the earth on which you live is shaped like a ball, does it not seem that a big ball would be a good sign for the earth?

The size of the sign. — Remember that the map in Figure 37, although it is only a few inches long, stands for a region hundreds of miles long. Now hold your hands a little more than two and a half feet apart. Can you imagine aball that would reach at its widest part from one hand to the other? You would need to have a ball as large as this in order for it to be the right size for the map in Figure 37. Do you see that this map would cover only a very small part of a ball of that size? This shows you that, altough the region shown in this map is hundreds of miles long and hundreds of miles wide, it is indeed a small part of the whole world. To go round the world you must travel thousands and thousands of miles.

A smaller sign. — You can see that a ball two and a half feet through would be a very hard sign to handle. Suppose you think of a smaller ball. Hold your hands eighteen inches apart, and think of a ball eighteen inches through. In order to make a map of the land of the Tigris and Euphrates small enough for this world sign, you would have to make it the size of the one in Figure 38. This smaller map stands for just the same things that the larger one does. You might run races to see which of you can finish first a list of fifteen things which the signs in Figure 38 suggest to you. Does this help you to see that a small sign for the world can stand for just as many things as a larger sign stands for?

Another kind of world sign. — Although a ball is the best sign for the whole earth, a ball cannot be put into a book. There can be put into a book, however, the picture of a ball, such as the picture in Figure 39. Of course in this figure you can see only the half of the ball nearest you. There would have to be two pictures in order to show both halves of the ball.

Putting signs on the world sign. — A map of the land of the Tigris and Euphrates that is the right size for this world sign must be even smaller than the one in Figure 38, but it stands for just as much as the larger maps. Figure 40 shows how this map fits on the world sign. As you look at this figure, think again of the hundreds of miles you journeyed along the Tigris. Notice, too, that the land of the Tigris and Euphrates is a very small part of the half of the world for which this sign stands. Even this small world sign, then, helps to show you that the world is very, very large. As you make other journeys, more and more signs that will remind you of them will be added to the world sign. At last, you will have a map of the world.

Two puzzling questions. — A little boy or girl who thinks carefully about the shape of the earth, usually thinks of two puzzling questions. 1. If the earth is round, why does it seem flat? 2. Are people on the opposite side of the earth from us standing feet up, head down? Had you thought already of these two questions? The following paragraphs answer these questions for you.

Why the earth seems flat. — Notice the lines in Figure 41. All these lines are exactly the same length. Line I is part of a small circle. Line II is part of a somewhat larger circle. Line III is part of a circle 8 feet across. If you could see at one time the whole circle of which Line III is a part, you would see the curve just as easily as you can in I. But since you see only a small part of this circle, the line seems almost straight.

Suppose that instead of seeing a small part of a circle eight feet across, you were to see a tiny part of a circle that is eight thousand miles across. Do you think that you could tell that it is curved? A great circle drawn around the earth would be almost 25,000 miles long, and’ almost 8ooo miles across. Does that help you see why the earth seems flat to you? You can see at one time such a tiny, tiny part of the millions of square miles of land and sea on the earth that the part you see does not seem curved. In order to see the earth as it is shown in your map, you would have to be far enough away to see, all at once, the half of the earth nearest you. Of course no one has had this view of it, but men have learned in other ways that the earth would look like a ball if they could see it from the moon or from some such far-off place.

"Up" and "Down." — "Down" is the direction in which things fall when they are dropped. "Up"is the opposite direction.

Did you ever see a magnet? Did you ever watch a magnet pull a needle to it? Did you not wonder how the magnet could pull the needle? After watching the magnet and the needle carefully, you know that there must be a force there which you cannot see, or the needle would not move.

In the earth there is a force somewhat like the force of a magnet. No one can see it, but it pulls all people and all things toward the center of the earth. This is the reason why things always fall toward the earth instead of away from it. This force which pulls things toward the center of the earth is called gravity. Since "down" is the direction in which things fall, " down "means toward the center of the earth. "Up" means away from the center of the earth.

Suppose you could go from your home eight thousand miles right through the center of the earth to the part of the surface of the earth just opposite you. You would go down, down, down, with the pull of this force called gravity, till you came to the center. But as soon as you passed the center on this journey straight through the earth, you would be going away from the center, not toward it. You would be going against the pull of gravity, not with it. You would be going not in the direction in which things fall, but in the opposite direction. You would be going "up" instead of "down."

Children on the opposite side of the earth, then, are standing head up, feet down, just as you are, for their feet are toward the center of the earth and their heads away from the center.

Perhaps these paragraphs about gravity are too hard for you to understand. If they are, don’t worry about it. You will understand such things when you are older. Just remember — "Down" means toward the center of the earth. "Up" means away from the center of the earth.

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