TUTOR. Well, Sir! I suppose this early visit is in consequence of my promise, and your anxiety to become an astronomer. PUPIL. It is, Sir.—And as astronomy is a science of which I have a very imperfect idea, I must beg of you to explain it to me. TUTOR. That I shall do with pleasure. But you surely cannot wholly forget what I have formerly told you. However, as I mean to treat the subject as if you had no previous knowledge of it, you will have an opportunity from what you can recollect, to make such remarks, and ask such questions, as may appear most material to you. PUPIL. I thank you, Sir, it is just what I wish. TUTOR. By astronomy then is meant a knowledge of the heavenly bodies, the sun, moon, planets, comets, and stars, respecting their nature, magnitudes, distances, motions, &c. PUPIL. I fear I shall find it a difficult study. TUTOR. Have patience.—— “The wise and prudent conquer difficulties, “By daring to attempt them. Sloth and folly “Shiver and shrink at sight of toil and danger, “And make the impossibility they fear.” PUPIL. This gives me encouragement, and, if you will have patience with me, I will endeavour to profit by your instructions.——Pray, Sir, what is the sun? TUTOR. The sun, the source of light and heat, has been considered a globe of fire, round which seven other spherical bodies revolve at different distances from him, and in different periods of time, from west by south to east. These are the planets[1]. [Footnote 1: From _Planeta_, roving or wandering.] PUPIL. Any round ball is a globe, is it not? TUTOR. A sphere or globe is defined a round solid body, every part of whose surface is equally distant from a point within called its center; and a line drawn from one side through the center to the opposite side, is called its diameter. PUPIL. You say the sun has been considered a globe of fire. Is he not now thought to be so? TUTOR. [2]Doctor Herschell, from some late observations, is of a different opinion.—But what think you of his magnitude? [Footnote 2: See his letter read at the Royal Society, December 18th, 1794.] PUPIL. I really cannot conjecture.—This I know, that when I saw him through the fog the other day, he appeared about the size of a common plate. TUTOR. You must not always judge by appearances. You will find that there is a material difference between his real and apparent magnitude, which I think you will be convinced of when I tell you, that he is no less than 95 millions of miles from our earth. PUPIL. Ninety-five millions of miles! You astonish me. TUTOR. You will, I dare say, be no less surprized at being told, that he is more than a million of times as large as our earth. PUPIL. It is almost incredible! And what are the planets?