CHAPTER XXI.

SCHEDULE I. (STANDARD VII.).

READING and WRITING as in Standard VI.

"In Standard VII., in order to warrant a pass, the theme should exhibit something more of structural character and arrangement, the sense should be clear, the expressions fairly well chosen, and the writing, spelling, and grammar free from ordinary faults." (Instructions to Inspectors.)

ARITHMETIC.-"Averages, Percentages, Discount, Stocks." (New Code, 1883.)

SCHEDULE II.: CLASS SUBJECTS.

ENGLISH.-Recitation or Analysis as in VI. (See

p. 292.)

"To know prefixes and terminations generally.” (New Code, 1883.)

GEOGRAPHY.- "The Ocean, Currents, and Tides; General arrangement of the Planetary System; the Phases of the Moon."

For the Ocean, Currents, and Tides, the "Pupil Teacher's Geography," "America and the Oceans," may be consulted. In addition, the following pages will furnish condensed teaching notes :

:

GENERAL ARRANGEMENT OF THE PLANETARY SYSTEM.-By

means of a diagram, or drawing made on the blackboard by the teacher, the Solar System should be explained. This has the sun in the centre, round which the planets revolve in orbits at different distances. Around the planets the satellites likewise revolve. The planets nearer the sun than the earth are called the inferior, those without the earth's orbit the superior planets. The former comprise Mercury and Venus; the latter, Mars, the minor planets, Jupiter, Saturn, Uranus, and Neptune. The inferior undergo phases like the moon, and for similar reasons.

When an inferior planet, the sun, and the earth are in one straight line, the planet is said to be in conjunction; viz. "superior conjunction," when on the other side of the sun; "inferior," when on the same side as the earth.

When a superior planet is on the opposite side of the heavens from the sun and nearest the earth, it is said to be in opposition; when on the same side, and farthest from the earth, in conjunction.

The planes of the orbits of the planets to the ecliptic (the plane of the earth's orbit) vary; as does also the time of their revolution on their axes, and of their revolution round the sun.

The orbit of each planet is an ellipse, of which the sun is in one focus (centre of an ellipse); therefore their distances from the sun vary at different times, as is the case with the earth.

There is a certain proportion between the times of the revolutions of the planets round the sun, and of their distances from it.

The path of the planets is dependent upon an original impulsive force sending the planet away from the sun (centrifugal force), and the attraction of the sun, drawing the planets towards it (centripetal force). These two forces are obeyed by the planet taking a circular course round the centre of the solar system (the sun).

The minor planets number rather more than one hundred. The planets which have satellites (moons) are the Earth (1), Jupiter (4), Saturn (8), Uranus (4), and Neptune (1). The four nearest planets to the sun are smaller than the rest, and very dense (heavy); the four exterior are very large, and not so dense.

MERCURY shows like a star close to the sun, in the west a little after sunset, or in the east a little before sunrise. It is about three thousand miles in diameter. When it comes direct between the earth and the sun it is said to be in transit, and appears on the sun like a round black spot.

VENUS. This is the most brilliant of the planets; distant about sixty-six million miles from the sun; its diameter is about seven thousand five hundred miles. It is known as the "Morning" and "Evening Star," when seen at sunrise and sunset near the sun, and is often visible to the naked eye. It has transits like those of Mercury.

THE EARTH is distant from the sun about ninety-one millions of miles; is about eight thousand miles in diameter, and, like the others, is flattened at the poles, and has a diurnal and annual motion, the former on its own axis, the latter round the sun.

Proofs of Rotundity.-(1) It has been circumnavigated in every direction which the configuration of the land allows.

(2) When a vessel recedes from the land, a spectator on shore loses sight of the hull, then of the lower sails, and finally of the tops of the masts. To those on board, the reverse phenomenon is observed; they lose sight of the shore, then of the houses, then of the tops of spires, and lastly of the tops of high hills (and mountains if any are in the vicinity). These appearances must be occasioned by the convex shape of the earth intervening between the shore and vessel. The effect of distance only diminishes the size and brightness of objects, and in no way alters their forms.

(3) The sun rises earlier to the east and later to the west of us, but if the earth were a plane he would be visible Over all the world at the same time. Sunrise is earlier six seconds for every mile we travel eastward in Great Britain.

(4) If we travel north or south, the pole star appears to ascend or descend according to the space passed over, and while stars with which we are familiar will appear to sink new stars appear.

(5) When ascending after sunset, aeronauts have observed that as they do so the sun comes again into view, rising on their western horizon, while the earth below them is in profound darkness. If the earth were a plane, a slight depression below the horizon would cast in shadow the highest altitude to which the aeronaut could ascend.

(6) In eclipses of the moon the shadow is always circular, and no other body than a sphere casts a circular shadow in whatever direction the light may shine on it.

(7) In construction of canals and similar hydrographic works, an allowance of eight inches to the mile must be made for the earth's curvature. This also affords an idea of its size-a globe requires a diameter of 7920 miles to allow a curvature of eight inches to the mile.

(8) If on a level sheet of water of considerable extent three staves six feet in length be erected, one in the centre and one at each end, and we look from the top of the first to that of the last, it will be found that the line of sight intersects the central staff at a distance from the top, depending on the length of the sheet of water on whose surface the experiment is tried. This proves that the surface of the water is not level, but heaped up at the

centre.

(9) In accordance with its motion as a planet, it could have no other form.

(10) Three angles of every plane triangle are together

two right angles, while three angles of a spherical triangle are together greater than two right angles. In trigonometrical surveys it has been observed that the sum of three angles of triangles drawn on its surface is greater than two right angles. Consequently the earth must be spherical.

(11) The reflection from convex mirrors gives different images from those of plane mirrors; and the images of trees, houses, etc., thrown from the surfaces of lakes are such only as could be given from convex surfaces.

MARS is of a fiery red colour, and is about half the diameter of the earth, its day being nearly twenty-four hours long.

THE MINOR PLANETS fill the gap between Mars and Jupiter, and hence their existence was suspected before they were detected by the telescope.

They are of very varying size, but all small, one only twelve miles in diameter.

JUPITER is the largest of the planets, its diameter being more than ten times that of the earth, giving a size 10 = 1000 times greater than our planet's. It is often visible to the naked eye. When seen through the telescope, it appears belted in parallel lines. It takes only about ten hours to revolve on its axis, so that its day (and night) is about ten hours long. Its four satellites can be seen only with the telescope.

SATURN is the next largest planet, its diameter being nearly ten times that of the earth. It is visible to the naked eye when nearest the earth (at opposition), and is "belted" like Jupiter.

It has a broad, thin, flat ring round it, separated from the main body of the planet, and this ring casts a shadow on the planet. The satellites of Saturn are eight in number, each revolving on its own axis, and travelling round the planet.