Each degree is divided into 60 equal parts, called minutes, and each minute into 60 equal parts, called seconds. Questions for Review. How many degrees are there in the circumference of the earth? How many miles in a degree? How many miles in the circumference of the earth? How many minutes in a degree? SECTION XIII. Latitude. You have learned that the earth is round, like a ball: I wish now to teach you how distances are measured on its surface. You see these parallel lines running east and west, on the map of the world (or globe). These lines are called parallels of latitude. One of these lines passes round the middle of the earth, and is made thicker than the rest. This is called the equator. It is so called, because, when the sun is directly over that line, the days and nights are equal all over the world. Can you tell me at what times of the year the days and nights are equal? If you should continue to travel north from this line, you would come to a place which is called the north pole; and if you should travel south just as far, you would come to the south pole; and both these distances together, you see, make half the circumference of the globe. How many degrees are there in half the cir cumference? How many from the equator to each pole? If a place is half way between the equator and either pole, how many degrees will it be? These are called degrees of latitude. If a place is north of the equator, it is in north latitude. If it is south of the equator, it is in south latitude. Are the United States in north or south latitude? In some maps the parallel lines are drawn 10 degrees apart, in some five degrees, and in some only one degree, or half a degree, or one fourth of a degree, &c. The figures on the edges of the map will show us how far the lines are apart. [The teacher should explain this subject fully, by referring to different maps. The scale of miles should also be explained, and applied, by means of a pair of dividers, or a strip of paper, to the measurement of distances.] Is Great Britain in north or south latitude? Why? Canada? Colombia? Peru? Egypt? New Holland? China? Madagascar? Questions for Review. What are parallels of latitude? Why is it called the equator? When in S. latitude? How far apart are the parallels of latitude drawn on maps? How are these distances marked on maps? SECTION XIV Longitude. Besides the parallels of latitude, there are other lines on the globe, and on maps, which run north and south. These you perceive, on the map of the world, or globe, are not parallel, but approach each other nearer and nearer, as we go from the equator, till they meet in the north and south poles. We make use of these lines in measuring distances east or west. They are called lines of longitude, or meridian lines. The principal meridian line is that which is marked with a cipher on the equator, and is called the meridian of London, because it passes near the city of London. In most maps these distances are marked on the upper and lower margins, as the degrees of latitude are noted on the margins at the right hand and left. If a place is east of London, it is east longitude; if west, it is west longitude; and if it is directly on the opposite side of the globe, or 180 degrees from the meridian of London, it is neither east nor west longitude. Can you now tell me whether the United States are in east or west longitude? Why? Is Mexico in E. or W. longitude? The whole American continent? Asia? Are Europe and Africa most in east or west longitude? I have told you that the sun passes directly over that part of the earth where the equator is drawn does it ever come directly over this place? Does it come more nearly over our heads at some seasons of the year than at others? When does it appear to come nearest to us? When does it seem to be farthest off? Then the sun does not always appear to move through the same part of the sky, does it? You are right: the sun passes over the equator about the 20th of March, when the days and nights are equal. It then comes farther and farther north every day, till the 21st of June, when the days are the longest, and the nights shortest. Then it appears to go back every day, farther south, till it crosses the equator, Sept. 23d, when the days and nights are again equal. It continues to go farther and farther south, till the 21st of December, when the days are shortest, and the nights longest. Then, again, it begins to come back towards the north; and so it continues to do every year. Can you tell me now, why it is hottest in the summer, and coldest in the winter? Questions for Review In what direction are the lines of longitude drawn? Are they parallel on the map of the world, or globe? Where do they meet? What use do we make of these lines? Which is the principal meridian? In what part of the map are degrees of longitude marked? When is a place said to be in east longitude? When in west longitude? At what times in the year does the sun pass directly over the equator? At what time are the days the longest? At what time are the nights the longest? SECTION XV. The Zones. What should you think of those parts of the earth, near the equator, directly over which the sun passes, at some seasons of the year? Is the weather hot, or cold? |