What is its diameter ?

What is the name of the sixth ?

By whom was it discovered? And when?

What is its color?

For what is it distinguished?

What is its distance from the Sun ?

What is the time of its tropical revolution?

What is its diameter ?

What is its apparent diameter as seen from the Sun? What is the name of the seventh ?

By whom was it first discovered?

In what year ?

What is the height of its atmosphere ?

In what time does this planet perform its revolution round the Sun ?

What is her distance from that luminary?

What is the name of the eighth planet from the Sun ? When was it discovered? And by whom?

What is its distance from the Sun ?

In what time does it perform its annual revolution around him?

What is the height of its atmosphere ?

By what name are the last four collectively called? They are called Asteroids.

What is the name of the ninth planet from the Sun ? How many miles distant from the Sun ?

What is his diameter ?

In what time does he perform his annual revolution? In what time on his own axis?

What is his mean motion in his orbit?

What is his mean motion on his axis?

Have the inhabitants of Jupiter any sensible change of seasons?

How many miles constitute a degree on this planet? How many miles difference between his equatorial and polar diameters?

Why is this great difference?

How many degrees is the orbit of Jupiter inclined to the Ecliptic? In what sign of the Zodiac is his north node? In what sign his south node ?

How many satellites attend this planet? What is his apparent diameter as seen from the Sun? What as seen from the Earth?

Of what benefit have those Moons been to the inhabitants of this Earth? Can either of them be seen by us without the aid of telescopes?

What name is given to the next, or tenth planet from the Sun ?

What is its distance from the Sun?

How many miles does this planet move in an hour? In what time does it perform its revolution around the Sun? In what time on its own axis?

What is its diameter ?

What is his mean apparent diameter as seen from the Sun? What as seen from the Earth?

How many degrees is its axis inclined to its orbit ? What encircles his body?

How does it appear when viewed with a telescope? What is its breadth ?

How does it appear to the inhabitants of Saturn?

Why is it sometimes invisible to us?

How many times does it appear in one revolution of the planet ?

In what signs and degrees of the Ecliptic does it disappear?

In what signs and degrees does this ring appear most open?

How many Satellites has this planet?

Where are they situated, inside or outside of the ring?

What is the form of this planet?

What is the name of the next, or outermost planet? When was it discovered?

How far is it situated from the Sun?

In what time does it perform its annual revolution? What is its diameter ?

What is its apparent diameter as seen from the Sun ? What as seen from the Earth?

Can it be seen without the aid of a telescope?

How many Satellites attend it?

In what direction do those Satellites move?

What are Comets ?

In what direction do they move?

In what part of its orbit is its train most brilliant ?

What was Newton's opinion concerning the Comet's tail, or train?

How many Comets are supposed to belong to the Solar System?

How many are known not to exceed the circuit of Uranus?

What would be the result if a Comet should come in actual collision with this Earth?

Is it probable that there will ever be such an oecurrence?

Why is it not probable ?

SECTION THIRD.

ON GRAVITY.

THE power by which bodies fall towards the Earth, is Called GRAVITY, or Attraction. By this power in the Earth, it is that all the bodies on whatever side, fall in lines perpendicular to its surface. On opposite parts of the Earth, bodies fall in opposite directions, all towards the centre, where the whole force of gravity appears to be accumulated. By this power constantly Earth, they are kept from

acting on bodies near the leaving it, and those on its they cannot fall from it.

surface are kept by it, that Bodies thrown with any ob

liquity, are drawn by this power from a straight line into a curve, until they fall to the ground. The greater the force with which they are projected, the greater is the distance they are carried before they fall. If we suppose a body carried several miles above the surface of the Earth, and there projected in an horizontal direction, with so great a velocity that it moves more than semidiameter of the Earth in the line, it would take to