Pupil. May we not then doubt whether she be inhabited or not, as without air we cannot breathe?
Tutor. The same Almighty Being who created us and gave us air to breathe, may have provided a different way for their existence. It does not hold good that, because we could not live there, she is not inhabited. Fish will live a considerable time in water under an exhausted receiver: and, I have heard of a toad being found in a block of marble. Your doubt therefore, I think, ought not to be admitted.
Pupil. I am satisfied. And must now beg to be informed how I may observe the moon’s motion.
Tutor. Her real motion round the earth, may be easily known by remarking when she is near any particular star. Thus, suppose you see her west, that is to the right of it, she will be approaching, then in conjunction with, and afterwards pass it towards the east. Her apparent motion is that of rising and setting, which is occasioned by the rotation of the earth on its axis.
Pupil. I remember not long since, when you shewed me Jupiter, that the moon was west of him: the next evening I saw her almost appear to touch him, and soon after at a great distance from him easterly. I now see that her real motion is from west by south to east, and her apparent motion from east by south to west.
Tutor. If you have no objection, I will now explain the cause of eclipses.
Pupil. So far from it, that it will give me the greatest pleasure.
Tutor. Take your ivory ball, suspend it as before, in a right line between your eye and the candle.—Can you see the candle?
Pupil. No, Sir.
Tutor. For what reason.