Part 3

N^o. 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 Plate II) that many distinguished philosophers are of opinion, they are but the fragments of One large Planet, which, from some cause or other, has burst.—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.

N^o. V. ]

RECAPITULATION OF LESSON II.

QUESTIONS.

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 Plate III. 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 to compare the different magnitudes of the Planets and their Diameters.

FOOTNOTES:

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.

LESSON III.

EXPLAINING THE MOTION OF THE PLANETS AND COMETS ROUND THE SUN.

§ 14. You have learned, in the preceding lesson, that the Earth and the other Planets are regularly moving round the Sun; but you must know that the time which each requires to complete a whole revolution, that is, the time which each needs to move once round, cannot be the same with all; as you may easily judge yourself: for the Planets which are next to the Sun will, of course, have a much smaller journey to perform, than those which are further from it. Thus Mercury, which is the first Planet in order from the Sun, will naturally come round much sooner than Jupiter, which is placed at a much greater distance from it.

That you may the easier understand this, the following Plate, No. VI, will represent to you our Solar System:

The Sun from which proceeds all light and heat, is placed in the centre. Then come the Planets Mercury and Venus; Third in order is our Earth with its Satellite the Moon; and so on. The rest of the Planets in the same order in which they are represented on Plate II. You will also perceive there the orbs of two Comets, distinguished as you were told, by a tail of light. The Planets Jupiter, Saturn and Herschel are each represented with their Moons, and the Planet Saturn with its luminous ring.

N^o. VI. ]

Now you will easily understand that Ceres, Vesta, Juno, Pallas, Mars, Jupiter, Saturn and Herschel, have each a much greater distance to travel, than our Earth; but that, on the contrary, Venus and Mercury can complete their revolution in a much shorter time.