Pupil. Pray, Sir, how may I know them?
Tutor. By studying the use of the cælestial globe, on which they are drawn.
Pupil. Will you be kind enough to instruct me, Sir?
Tutor. At some future time I probably may: at present you are not prepared for it.
Pupil. I am satisfied.—Have you any thing more to remark of the constellations, Sir?
Tutor. Yes. The situation of the planets, as they are continually changing their places, could not be pointed out without first dividing the stars into constellations: hence, necessity was the mother of invention.
Pupil. And I think a very ingenious one.—If I may be allowed a comparison, I will suppose the different kingdoms of the world on my dissected map, to represent so many constellations; then, if I hear of London, I know it is in England; if of Paris, in France; of Lisbon, in Portugal; and so on. These I would compare with stars of the first magnitude, being the chief cities of their respective kingdoms; inferior cities, stars of the second magnitude; principal towns of the third, &c.
Tutor. A very apt comparison indeed. Now if you hear of a traveller setting off from London to Dover, thence to Calais, Paris, Bern, and so on to Rome, you know that he must go through part of England, Flanders, France, Switzerland, and Italy, passing many towns and villages on his way.
Pupil. That is very evident.
Tutor. Very well, then; in like manner would the planets, if seen from the sun, be traced from star to star, from constellation to constellation, through their whole periods.