Are these the only variations to which the spots are apparently subject?

No: when the moon is in, or near opposition, a very remarkable change in its general appearance takes place. The whole disk appears illuminated, and reflects the sun's rays directly on the earth; many of the shadows. projected by the eminences on her surface disappear; and, in fact, the change is so great as to render it difficult to recognise many of the spots.

Has the moon two motions, the same as the earth, one round its own axis, another round the earth?

Yes; and this revolution round the earth is performed in a little more than twenty-seven days; and you are aware, that to the inhabitants of the moon the earth appears to revolve about them in exactly the same period of time.

Yes: and you have just told me, that the earth and moon are bodies of the same nature; so I suppose, that, as the moon is capable of reflecting the light received from the sun, the earth is capable of doing the same?

That is a very proper conclusion; and it is a fact that our earth is a moon, to the moon, appearing thirteen times larger to her, than she does to us.

O mamma, what a majestic sight!

At the time of new moon to us, the earth appears to the inhabitants of the moon, full; but, as the moon turns upon its axis only once during a month, and as we have always nearly the same face presented to us, it is evident, that the residents on one half of the lunar world never enjoy the glorious sight of the earth.

I am sure, I should take a journey to the opposite hemisphere, were it my misfortune to live on the unillumined side.

Yes, I hope you would; for I cannot figure to myself an object more interesting than the sight of a globe gliding majestically along the azure vault of heaven, and affording as much light as thirteen of our highly valued moons. Should any of the inhabitants feel as you do, in comparing it with the sun, they may well say,

"Thou giv'st us his blaze again

Void of its flame, and shedd'st a softer day."

CHAPTER VIII.

SECTION THE FIRST.

THE SUN, THE EARTH, AND THE MOON.

FOR the sake of method we have considered these interesting bodies under three divisions; but to see in a more perfect manner the simplicity, and grandeur, of Nature in her designs, and the wisdom, and the simplicity, of her workmanship, we must no longer separate them, but must view them in their collective operation, in their mutual subserviency and dependence, in their combining together to produce one result, one grand and interesting design. The most astonishing effects are the result of a few simple principles; the same invariable laws, govern alike the indiscernible atom, and the immeasurable body; the single principle of gravitation, pervades the whole universe, and puts every spring, and wheel, of it in motion.

What subject will you first select, mamma, in considering the united influence of the sun, the earth, and the moon?

We will, for a few moments, turn our minds to the pleasing vicissitudes, exhibited in the

alternate succession of day, and night, and in the regular return of the seasons. You can, I am sure, tell me in what way these are produced.

Is not the succession of day, and night, occasioned by the uniform rotation of the earth on its axis?

It is; for, as the globe turns regularly round this imaginary line, once in every twenty-four hours, only one half of it can be illuminated at a time. Hence, it is evident, that any particu lar place will sometimes be turned towards the sun, and sometimes from it: and, being constantly subject to these various positions, it will enjoy a regular return of light and darkness. As long as the place continues in the enlightened hemisphere, it will be day; and when, by the diurnal rotation of the earth, it is carried into the dark hemisphere, it will be night.

In what direction is this motion of the earth on its axis performed?

It is from west to east; and this occasions an apparent motion of the celestial bodies in a contrary direction.—The sun, for instance, seems to make his daily progress through the heavens, from the east towards the west; but this is an optical illusion, arising from the opposite motion. of the earth.

If the axis of the earth were perpendicular to the plane of its orbit, should we not have the days, and nights, equal all over the globe?

Yes; for, if this was the case, the boundary of light and darkness would pass through the two poles, and divide each of the small circles, which are parallel to the equator, into two equal parts; and, as the uniform rotation of the earth upon its axis, must occasion every place to describe equal parts of one of these parallel circles in equal times, the days and nights would of course be equal all over the globe, except at the poles, where the sun would neither rise nor set, but remain continually in the horizon.

But, as the axis of the earth is inclined to the plane of its orbit, what is the result?

The result is, that the days lengthen, and shorten, from the equator to the polar circles, every year, the greatest length being six months, the least length being twelve hours; so that there is sometimes no day or night for many revolutions of the earth within the polar circles, and the days and nights are equally long all the year round at the equator, which is always equally cut by the boundary line of light and darkness.

But, during the six months' darkness at the poles, what is the compensation to the inhabitants?

As one half of the ecliptic never sets, and the other never rises, at the poles, the inhabitants would certainly be in darkness during six months, were it not for the intervention of