I am afraid, Sir, I am come before you are prepared for me: but the very great pleasure I received yesterday, induced me to be with you as early as possible.

Tutor. I am glad to see you, and happy to find you are so well pleased with your difficult study. It will, I assure you, give you more exalted ideas of the Deity than any that I know of. The Psalmist was undoubtedly of this opinion when he said, The Heavens declare the glory of God, and the Firmament sheweth his handy work.

Pupil. I will no longer call it a difficult, but a pleasing study, and feel myself ashamed at having used the expression. I shall now beg you to explain to me the different systems.

Tutor. The system I have been describing to you was known and taught by Pythagoras, a Greek philosopher, who flourished about 500 years before Christ, as he found it impossible, in any other way, to give a consistent account of the heavenly motions.

This system, however, was so extremely opposite to all the prejudices of sense and opinion, that it never made any great progress, nor was ever widely spread in the ancient world.

Ptolemy, an Egyptian philosopher, who flourished 130 years after Christ, supposed that the earth was fixed in the center, and that the sun and the rest of the heavenly bodies moved round it in twenty-four hours, or one natural day, as this seemed to correspond with the sensible appearances of the coelestial motions. This system was maintained from the time of Ptolemy to the revival of learning in the sixteenth century.

At length, Copernicus, a native of Poland, a bold and original genius, adopted the Pythagorean system, and published it to the world in the year 1530. This doctrine had been so long in obscurity, that the restorer of it was considered as the inventor.

Europe, however, was still immersed in ignorance; and the general ideas of the world were not able to keep pace with those of a refined philosophy. This occasioned Copernicus to have few abettors, but many opponents. Tycho Brahe, in particular, a noble Dane, sensible of the defects of the Ptolemaic system, but unwilling to acknowledge the motion of the earth, endeavoured, about 1586, to establish a new system of his own; but, as this proved to be still more absurd than that of Ptolemy, it was soon exploded, and gave way to the ^[8]Copernican or true Solar System.

Pupil. I confess, I should have thought with Ptolemy, that the earth was in the center, and that the sun moved round it.

Tutor. You must at present content yourself with knowing that it is not so; and it shall be my business to prove it.

Pupil. May I beg the favour of the information you intended respecting the planets?

Tutor. I will grant it with pleasure. The planets are spherical bodies, which appear like stars, but are not luminous; that is, they have no light in themselves; though they give us light; for they shine by reflecting the light of the sun.

Pupil. You say, Sir, that they appear like stars; if so, how am I to know them from stars?

Tutor. Very easily: for the stars, or as they are more properly called fixed stars, always keep the same situation with respect to each other; whereas the planets, as they move round the sun, must be continually changing their places among the fixed stars, and with one another.

Pupil. Is there any other method of distinguishing them besides what you have mentioned?

Tutor. Yes. The planets never twinkle like the fixed stars, and are seen earliest in the evening and latest in the morning.

Pupil. How is the twinkling of the stars in a clear night accounted for?

Tutor. It arises from the continual agitation of the air or atmosphere through which we view them; the particles of air being always in motion, will cause a twinkling in any distant luminous body, which shines with a strong light.

Pupil. Then, I suppose, the planets not being luminous, is the reason why they do not twinkle.

Tutor. Most certainly. The feeble light with which they shine is not sufficient to cause such an appearance.

Pupil. Have the stars then light in themselves?

Tutor. They undoubtedly shine with their own native light, or we should not see even the nearest of them: the distance being so immensely great, that if a cannon-ball were to travel from it to the sun, with the same velocity with which it left the cannon, it would be more than 1 million, 868 thousand years, before it reached it.^[9]

Pupil. This is wonderful indeed! what then are they supposed to be?

Tutor. Suns.

Pupil. Suns! the fixed stars suns!

Tutor. Yes, suns.

And what will increase your astonishment, each of them is the center of a system of planets, which move round him.^[10]

Pupil. I am almost lost.—I used to think they were designed to give us light.

Tutor. This is a vulgar error.—They were doubtless created for a much nobler purpose, since thousands of them are invisible to us without the help of a telescope; and we receive more light from the moon than from all the stars together.

Pupil. How do you know they are suns? Is their being luminous a proof of their being so?

Tutor. No. But we know that the sun shines with his own light on all the planets belonging to our system; and from what I have told you, have the greatest reason to believe that the stars shine with their own light: we therefore from analogy conclude, that they are so many suns conveying light and heat to other worlds^[11].

Pupil. Are there then other worlds besides this we live in?

Tutor. Consider.—Has not the earth we inhabit a moon to enlighten it?

Pupil. Yes, Sir.

Tutor. And have I not told you that Jupiter, Saturn, and Georgian, have also moons?

Pupil. This I well remember.

Tutor. For what purpose then do you suppose those orbs were designed?

Pupil. Indeed, I cannot tell.

Tutor. You surely cannot imagine that they were intended for our use, since we knew nothing of them till after the invention of telescopes.

Pupil. That is what I think no one can suppose.

Tutor. And do not all the planets enjoy the benefit of the sun in common with us?

Pupil. Undoubtedly.

Tutor. Well, then; of what use would the light and heat be which is conveyed to them from the sun; or the light which they receive from their moons if there are no inhabitants?

Pupil. I know of none.

Tutor. Can you then have any doubt about their being inhabited?

Pupil. No, Sir.—But you say that the stars are suns, each of which is the center of a system of planets or worlds.

Tutor. If you are satisfied that the planets belonging to our system are inhabited, and that the fixed stars are suns, the centers of other systems, what reasonable objection can you have to all the planets in the universe being so?

Pupil. It is what I cannot comprehend.

Tutor. It may be so.—But is not the same Almighty Power, who does nothing in vain, as capable of making ten thousand worlds if he pleased, as well as one?

Pupil. I will not presume to dispute his power; but are we not told that all mankind descended from Adam?

Tutor. Yes; Moses wrote concerning this earth, he has not made us acquainted with the inhabitants of the other planets: for aught we know they might descend from other Adams.—To-morrow evening, I hope to see you again.