visible to the eye in a clear night; but by the use of telescopes, it has been discovered that there are several millions. They are at an immense distance from us; and are supposed by many to be suns, enlightening other worlds.

8. Among these stars we find a few, distinguished by their steady light, which change their place continually, returning at given periods in the same path. They are hence called planets, or wandering stars; and when examined with telescopes, they are found to be globes, like our Earth.

[2] 9. On farther examination, it becomes evident that the Earth is also a planet, moving among the fixed stars; and all the planets are found to revolve round the Sun, at different distances, forming the solar system.

10. There are seven primary planets in our system, revolving round the Sun in the following order: 1. Mercury; 2. Venus; 3. The Earth; 4. Mars; 5. Jupiter; 6. Saturn; 7. Herschel, or the Georgium Sidus; as in the following figure :

The Sun is an immense body, a million times larger than the Earth, and 95,000,000 of miles from us, communicating light and heat to the whole system. It is 883,000 miles in diameter, and turns on its axis in twenty-five days.

Ve

Mercury is the smallest planet, so near the sun that it is seldom seen. nus is a bright star, nearly as large as the Earth. When it rises a short time before the sun, it is called the morning star; when it sets soon after the sun, the evening star. The Earth is about eight thousand miles in diameter, moving round the sun in one year, or 365 days 6 hours, at the rate of 68,000

miles an hour.

Mars is a planet much smaller than the Earth, of a red, fiery colour, and visible to the naked eye. Jupiter is nearly 1500 times larger than the Earth, and the largest of all the planets. It is usually surrounded with cloudy belts. Saturn is 1000 times larger than the Earth. It is surrounded by a broad, flat ring, divided into two portions, which revolve round it like satellites or [3] moons. Herschel, the most distant of the planets, is 90 times as large as the Earth, but it is seldom seen without a telescope.

There are 18 secondary planets, or moons, revolving round these primaries, of which the Earth has 1, Jupiter 4, Saturn 7, and Herschel 6. Our moon is only 2180 miles in diameter. It is 240,000 miles from the Earth, and revolves roun't it in 27 days.

Four very small planets, called asteroids,-Ceres, Pallas, Juno, and Vesta, have been discovered, revolving between the orbits of Mars and Jupiter.

Besides these, more than 400 comets, or stars with bright trains, have been seen revolving round the Sun.

The comets move irregularly, sometimes coming very near the Sun, and then flying off beyond the most distant planet. Only a few have been known to return, and at intervals of 75 to 100 or 200 years.

The following figures exhibit the usual appearance and comparative size of the planets.

11. The revolution of the Earth round the Sun is called the annual or yearly revolution, and causes the changes of the seasons. Its orbit, or path among the fixed stars, is called the ecliptic.

12. Besides this revolution, the Earth rotates, or turns like a wheel, on its own axis, once in twenty-four hours; and as the Sun enlightens only one half the globe at once, each part is alternately in the light and shade. This motion causes day and night, and is called the diurnal or daily revolution. In consequence of these motions of the Earth, the Sun appears to move round in the ecliptic every year, and to revolve round the Earth every day.

13. The other planets have similar revolutions, but in various times, as exhibited in the following table of their size, situation, and motions.

MATHEMATICAL DIVISIONS OF THE EARTH.

14. In describing the Earth, it is convenient to draw a number of imaginary lines or circles round it, in order to point out the situation of places, and the effects of the Earth's motions.

15. A great circle is one which divides the Earth into two equal parts or hemispheres. Others are termed small circles. 16. Every circle is divided into 360 degrees, (marked °,)— every degree into 60 geographical miles, or minutes, (marked ',) -and every minute into 60 seconds, (marked ".)

17. A degree on a great circle is about 69 English or common miles. On a small circle it is less, according to the

situation.

18. The ends of the axis of the Earth, or line on which it is supposed to turn, are called the north and south poles. (They are shown in figure 4, at N. and S.)

19. At equal distances from the two poles, a great circle is supposed to be drawn, (at E in the figure,) which is called the equator. It divides the Earth into two equal hemispheres; the northern hemisphere, in which we live, and the southern. (See this circle, and others mentioned hereafter, represented on the borders of the map of the world.)

20. The ecliptic, or orbit of the Earth, crosses the equator, and extends 23° 28′ on each side of it. When the Sun appears to reach this point, it turns again towards the equator.

21. Two circles are therefore drawn here, called tropics.* The northern is the Tropic of Cancer, the southern the Tropic of Capricorn.

22. When the Sun is over either of the tropics, as in June and December, it shines 23° 28′ beyond one pole, and leaves the same space round the opposite pole in darkness. Hence the two polar circles are drawn at this distance, which include all places whose longest day is more than twenty-four hours. The northern is called the Arctic Circle, and the southern the Antarctic.

23. Distance north or south of the equator is called latitude, and is measured in degrees, on the meridians. At the poles it is 90o, which it cannot exceed.

24. The small circles drawn parallel to the equator are [5] called parallels of latitude.

25. On the latitude of a place depends the heat of its climate, and the length of its days, as will be seen from the fol lowing remarks.

26. The Sun heats those parts of the Earth most, which are most directly exposed to its rays.

Thus in the figure, when the Sun shines directly or vertically upon any part of the Earth, as at S, it is evident that more of the rays strike on the same spot, than when it shines obliquely, as at W.

H

(3.)

27. The apparent path of the Sun is immediately over that belt or zone of the Earth, which lies between the Tropics; and it is vertical to every place in it, twice every year. Hence this is the hottest part of the Earth, and is called the burning or Torrid Zone.

28. The rays of the Sun strike most obliquely on those parts of the Earth which surround the poles. Hence the two zones within the polar circles, are the coldest parts of the earth, and are called the Frigid Zones.

29. The two zones between the tropics and polar circles, are generally free from the extremes of heat and cold, and are called the Temperate Zones.

*From the Greek rрenw; to turn.

30. The north pole of the Earth always points towards the north star in the heavens, and its axis is inclined to the ecliptic, as represented in the figure. This gives rise to the difference of seasons.

31. From March to September, the north pole is towards the Sun, and its rays fall most directly on the northern hemisphere, (as at S in figure 3,) producing summer. At the same time, [6] the south pole is turned away from the Sun; it shines obliquely on the southern hemisphere, and it is winter there.

32. From September to March, the south pole is presented more directly to the Sun; and the southern hemisphere is cheered with summer, while the northern is chilled with winter. In this way the two hemispheres always have opposite seasons. 33. The inclination of the Earth's axis to the ecliptic, also causes a variety in the days and nights of different parts of the Earth.

34. At the equator, the days and nights are always 12 hours each, and the Sun rises and sets at six o'clock throughout the year.

35. At the period of the equinoxes, (about the 20th of March and 22d of September,) when the Sun appears in the equator, the days and nights are equal in all parts of the world; but at other times, they vary in length according to the latitude and the season.

36. From March to September, the northern hemisphere is more than half enlightened, and the days are more than 12 hours long; and at the same time, the southern has less than 12 hours of light.