James. Then the length of a day and night in the moon is equal to more than 29 days and a half of ours.

Tutor. It is so: and therefore, as the length of her year, which is measured by her journey round the sun, is equal to that of ours, she can have but about twelve days and one-third in a year. Another remarkable circumstance relating to the moon is, that the hemisphere next the earth is never in darkness; for in the position E, when it is turned from the sun, it is illuminated by light reflected from the earth, in the same manner as we are enlightened by a full moon. But the other hemisphere of the moon has a fortnight's light and darkness by

turns.

Charles. Can the earth, then, be considered as a satellite to the moon? Tutor. It would, perhaps, be inaccurate to denominate the larger

body a satellite to the smaller: but, with regard to affording reflected light, the earth is to the moon what the moon is to the earth, and subject to the same changes of horned, gibbous, full, &c.

Charles. But it must appear much larger than the moon.

Tutor. The earth will appear, to the inhabitants of the moon, about 13 times as large as the moon appears to us. When it is new moon to us, it is full earth to them, and the reverse. James. Is the moon then inhabited as well as the earth?

Tutor. Though we cannot demonstrate this fact, yet there are many reasons to induce us to believe it; for the moon is a secondary planet of considerable size;-its surface is diversified like that of the earth with mountains and valleys;-the former

To

have been measured by Dr. Herschel, and some of them found to be about a mile in height. The situation of the moon, with respect to the sun, is much like that of the earth, and by rotation on her axis, and a small inclination on that axis to the plane of her orbit, she enjoys, though not a considerable, yet an agreeable variety of day and night and of seasons. the moon, our globe appears a capital satellite, undergoing the same changes of illumination as the moon does to the earth. The sun and stars rise and set there as they do here, and heavy bodies will fall on the moon as they do on the earth. Hence we are led to conclude that, like the earth, the moon also is inhabited. Dr. Herschel discovered some years ago three volcanoes, all burning in the moon; two of them appeared to him nearly

extinct, but the third showed an actual eruption of fire or luminous matter. He thought the eruption resembled a small piece of burning charcoal when it is covered by a thin coat of white ashes, which frequently adhere to it, when it has been ignited some time. But no large seas or tracts of water have been observed in the moon, nor is the existence of a lunar atmosphere certain. Therefore, her inhabitants must materially differ from those who live upon the earth.

CONVERSATION XV.

Of Eclipses.

CHARLES. Will you, sir, explain to us the nature and causes of eclipses?

Tutor. I will, with great pleasure. You must observe, then, that eclipses depend upon this simple principle, that all opaque or dark bodies, when exposed to any light, and therefore to the light of the sun, cast a shadow behind them in an opposite direction.

James.

The earth being a body of this kind, must cast a very large shadow on its side which is opposite to the sun.