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] [Footnote 9: The distance of Syrius is 18,717,442,690,526 miles. A cannon-ball going at the rate of 1143 miles an hour, would only reach the sun in about 1,868,307 years, 88 days. Adams’s Lectures, vol. 4. page 44.] PUPIL. This is wonderful indeed! what then are they supposed to be? TUTOR. Suns. PUPIL. Suns! the fixed stars suns! TUTOR. Yes, suns. “One sun by day, by night ten thousand shine.” And what will increase your astonishment, each of them is the center of a system of planets, which move round him.[10] [Footnote 10: Dr. Herschell says, that in some clusters of stars he has observed, they appear too close together to admit any planets to revolve about them.] “Observe how system into system runs.” “What other planets circle other suns.” 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]. [Footnote 11: Dr. Herschell thinks it probable that the sun and fixed stars may be inhabited.] 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.