[§ 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 the _Diameter_ of 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 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. [§ 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 of Jupiter’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. 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.