LESSON II.

OF THE PLANETS AND THEIR RELATIVE POSITION WITH REGARD TO THE SUN AND EACH OTHER.

§ 8. The Planets of which we have spoken in the First Lesson are Eleven in number, of which each has received a proper name. They are in the order in which they are placed from the Sun, the following:

The adjoining diagram, on Plate No.II, may serve for an illustration. You will see from it, that the Earth is the third Planet from the Sun. Mercury and Venus come before it; the most remote from the Sun isHerschel, so called from the astronomer’s name, who has but lately discovered it.

§ 9. The Earth is constantly attended by One Satellite (Lesson I, § 5); Jupiter by Four (see the diagram), Saturn by Six, and Herschel by Seven. Saturn is, besides, constantly surrounded by a broad luminous ring, which distinguishes it from all other Planets, and of which we shall speak hereafter.

§ 10. With regard to the magnitude of the different Planets it has been observed that although some of them are much larger than Our Earth; yet in Comparison to the Sun they are but small bodies, as you may see from the figures on plate No.III, in which the different Planets are drawn in proportion to the Sun: you will perceive from it;

1. That the Sun is a great many times[1]larger than either of the Planets.

No. II.

No. III..

2. That the Sun is much larger than all the Planets (our Earth included) taken together.

3. That Jupiter is the greatest Planet in our solar system.

4. That Saturn is the second Planet with regard to magnitude.

5. That Herschel ranks third.

6. That the Earth ranks fourth; but that

7. Each of the other Planets and the Moon are smaller than the Earth.

8. That either of the Planets Ceres, Vesta, Juno, Pallas is smaller than the Moon.

§ 11. If you cut a ball or a sphere in halves, and through the centre of one of the flat surfaces, draw a straight line across the whole surface, then this line is called theDiameterof the ball or sphere.—Now as the Sun and the Planets are nothing else but large balls or spheres (Lesson I, § 4), we may also speak of their Diameters.—Thus we say, “the Diameter of the Sun is so many times larger than that of the Earth; the Diameter of Jupiter is so many times larger than that of Venus,” etc.

You will now easily understand what the straight line means, which, in plate No.IIIis drawn through the centre of the circle, which represents the Sun; also the straight lines which are drawn through the circles which represent the Planets.—You will also perceive from the first figure on plate No.III, that the Sun’s Diameter is larger than the Diameters of all the Planets taken together.

§ 12. Plate No.IVrepresents thesurfacesof the Planets, compared to that of the Sun.—For you must know that it is possible tomeasurethe surface of a sphere; which is done by supposing it to be spread out, and then seeing how many square inches, feet or yards it contains. This we have supposed to be done with the surfaces of the Sun and Planets, and accordingly, have drawn their square measurements, in Plate No.IV. in proportion to each other.

You will see from this Plate:

1. That the square-Contents of the Sun’s surface is greater than that of the surfaces of all the Planets taken together.

2. That the square-Contents of the Earth’s surface is nearly as large as that of the surfaces of Mercury and Venus taken together.

No. IV.

3. That the square-Contents of the surfaces of Vesta, Ceres, Juno and Pallas, taken together, is not yet sufficient to cover the surface of our Earth.

4. That the square-Contents of Jupiter’s surface is larger than that of the surface of any other Planet.

5. That the square-Contents of Jupiter’s surface is greater than that of the surfaces of all other Planets taken together.

6. That Saturn’s surface is the next largest.

7. That Herschel’s is still larger than those of our Earth, Venus and Mercury taken together.

8. That the square-Contents of the Moon is nearly as large as that of the surfaces of Ceres, Vesta and Juno, taken together; and that it is larger than that of Pallas’ surface taken alone.

In order that you may be better able to compare, you will find on Plate No.V

1. The surfaces of the different Planets, all drawn upon the Sun’s surface; from which you may see, how much larger the Sun’s surface is than the surfaces of all the Planets and the Moon taken together.

2. The surface of the Earth compared to that of Mercury and Venus.

3. The Earth’s surface compared to that of the Four Asteroids Pallas, Ceres, Juno and Vesta.

4. Jupiter’s surface compared to those of all the other Planets.

5. The square-Contents of the Moon compared to the surfaces of Vesta, Juno and Ceres.

6. Herschel’s square-Contents compared to that of our Earth, Venus and Mercury taken together.

§ 13. The Four Planets, Ceres, Vesta, Juno, and Pallas, are so small in proportion to the other Planets, and are so near each other (they are almost at the same distance from the Sun—see PlateII) that many distinguished philosophers are of opinion, they are but the fragments of One large Planet, which, from some cause or other, hasburst.—But this is no subject for us now to inquire into;—we will therefore proceed to describe in the next lesson, the motion of the different Planets round the Sun.

No. V.

RECAPITULATION OF LESSON II.

QUESTIONS.

[§ 8.] What are the names of the Eleven Planetsin the order in which they are placed from the Sun? How many Planets are there between the Earth and the Sun? How many Planets come after our Earth? In what order then, is our Earth placed among the Planets? (Is it the first, second, etc. from the Sun)?

[§ 9.] How many satellites accompany our Earth? What is it called? How many satellites or Moons has Jupiter? How many has Saturn? How many has Herschel? By what is Saturn particularly distinguished from all other Planets?

[§ 10.] Are all Planets of the same magnitude as our Earth? Are the Planets in comparison to the Sun large or small bodies?—Is the Sun much larger than any of the Planets? Is the Sun larger or smaller than all the Planets, including our Earth, taken together? Which is the greatest of all Planets? Which Planet ranks, in magnitude, next to Jupiter? Which of the Planets ranks third in magnitude? Which, Fourth? What Planets are smaller than our Earth? What Planets are smaller than the Moon?

[§ 11.] What do you call theDiameterof a ball or sphere? Is the Diameter of the Sun larger or smaller than the Diameters of all the Planets taken together?

The teacher may yet ask a number of questions respecting the Diameters of the Planets, which the pupil will be able to answer by looking on PlateIII. He may, for instance, ask whether the Diameter of the Earth is larger or smaller than that of Venus? Whether the Diameter of Jupiter or Saturn is the largest, etc.? This will oblige the pupil tocomparethe different magnitudes of the Planets and their Diameters.

[§ 12.] What proportion does the square-Contents of the Sun’s surface bear to that of the surfaces of all the Planets? What two Planets have together a surface nearly as large as that of our Earth? Are the surfaces of Ceres, Vesta, Juno and Pallas taken together sufficient or not, to cover the surface of our Earth? What Planets, therefore, could be covered with the Earth’s surface? Which Planet has the largest surface? What do you observe with regard to the square-Contents ofJupiter’s surface? and that of the surfaces of all other Planets, taken together? What Planet’s surface comes next in magnitude to Jupiter’s? What Planet’s surface is larger than that of our Earth, Venus and Mercury taken together? What three Planets’ surfaces taken together are smaller than that of the Moon? What Planet has nearly as large a surface as the Moon?

[§ 13.] What is the opinion of philosophers respecting the Four Planets, Ceres, Vesta, Juno and Pallas?

FOOTNOTES:[1]Numbers are purposely omitted here, because abstract numbers convey little or no ideas to young pupils. Those who wish these relations expressed in numbers will find them in Table I at the end of the book.

[1]Numbers are purposely omitted here, because abstract numbers convey little or no ideas to young pupils. Those who wish these relations expressed in numbers will find them in Table I at the end of the book.

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