But, however decisive this may be, is there no other objection to the admission of the motion of those bodies round the earth?

Yes; the bulk of the heavenly bodies, compared with that of the earth, is a considerable objection.

How much larger is the sun, or are the stars, than the earth?

The sun is a million of times larger than the earth, and many of the stars are at least equally large.

To what then might we compare the motion of the sun round the earth?

"To the motion of a millstone round a marble." Are you satisfied?

But, mamma, while these are some of the objections to admitting the motion of the celestial bodies round the earth, are there any arguments in favour of attributing this motion to the earth?

Yes; such a motion will best account for all the celestial appearances, and at the same time preserves that beautiful simplicity and harmony, which is found to prevail in every other part of the creation.

But, if the earth moves, how is it that we do not perceive its motion?

We must remember that the earth is a very large body; and that the air, and all the things upon its surface, move with it in open space,

where it has no impediment to meet with in its way, to disturb its beautifully even motion.

To what may we compare the earth in its annual progress round the sun?

"To a balloon turning upon its axis, while it floats through the atmosphere."

But I have heard, that, if the earth really moved, a stone dropped from the top of a very high building, would not fall just at the bottom of it, for the building would advance considerably forward during the time of the fall.

This is a mistake; for "it is found by repeated experiments, that, if one body be thrown from another body in motion, the first body will partake of the motion of the second."

Will you be so kind as to illustrate this observation?

"A stone, dropped from the top of a mast, while the ship is under sail, is not left by the vessel, but falls exactly at the foot of the mast; and if a bottle of water should be hung up in a cabin with its neck downwards, it would empty itself drop by drop, into another bottle placed exactly underneath it, though the ship shall have run many feet while each drop was in the air."

By what term is this motion distinguished? This motion of the earth, which is round its own axis, is called its diurnal, or daily motion.

Is any periodical change produced by this

motion?

Yes; the regular return of day and night. Is the earth subject to any other motion ? To one other, which is called its annual motion.

Can the earth's annual motion be proved in the same way, as its diurnal?

The proofs may be easily gathered from celestial appearances in nearly the same manner as the former. For, as that luminary seems to move round the earth, from east to west in the space of a day, which is really owing to the diurnal revolution of the earth upon its axis, in a contrary direction; so, likewise, it seems to have an annual motion in the heavens, and to rise, and set continually in different parts of them, which is certainly occasioned by the daily motion of the earth in its orbit, or path round the sun, which it completes in the space of a year.

And will the revolutions and appearances of the different planets also prove, that the earth is not the centre of the celestial bodies?

Yes for it is evident, that wherever the sun be placed, the orbit of Venus surrounds, and encloses him, within itself; and therefore Venus, while she describes this orbit, must really move round the sun.

Will

you kindly illustrate the same fact by the motion of another planet?

Yes: Mercury is always found to keep in the neighbourhood of the sun, without ever receding from him so far as Venus. The extreme brightness of this planet, not only proves that it is nearer to the sun, than the other planets, but that it regards the sun as the centre of its motion.

What do you think, mamma, of Mars, Jupiter, Saturn, and the Georgium Sidus ?

These planets, being more distant from the sun than the earth, must necessarily include the earth in their orbits; but, from their appearances, it is plain, that the sun, and not the earth, must be the centre of their motions.

What is the conclusion you draw from all this?

That the earth, itself, must likewise move round the sun; for, since it has Mercury, and Venus, on one side nearer the sun, and Mars, Jupiter, Saturn, and the Georgium Sidus, on the other, more remote, it follows from analogy, that, being of the same nature as they are, it must also partake of the same motion.

CHAPTER VII.

OF THE MOON.

Is it possible, that my dear child can behold yon beauteous orb, without feeling an irresistible desire, to know something more respecting its character and influence? Let your tender mind kindle into devotion at such a season as the present, when this delicately beautiful planet is riding in awful majesty on high, attended by a multitude of lesser lights, which appear to follow in her train, or to decorate her path.

You know, mamma, how I love to hear you talk; attention does not tire me, difficulties do not discourage. I will, therefore, by immediately proposing a question to you, evince my anxiety to know more. While we are now looking at the moon, I observe a number of spots; what am I to understand they are?

Unassisted by the telescope, we naturally suppose, they are seas, and continents, mountains, and valleys; but on a more accurate inspection with the telescope we discern immense elevations and depressions, resembling the valleys, and mountains, on our earth.

And do you think, that they do not merely