with the convex fide turned from the fun; moving ftill to the eastward, the crefcent becomes more full; and when the moon comes to the meridian, about fix in the evening, she has again the appearance of a bright femicircle; advancing ftill to the eastward, fhe becomes fuller on the east fide; at last, in about 29 days, she is again oppofite to the fun, and again full.

It frequently happens, that the moon is eclipfed when at the full; that the fun is eclipfed fome time between the disappearance of the moon in the morning on the weft fide of the fun, and her appearance in the evening on the east fide of the fun. The nature of these phænomena will be more fully confidered, when we come to treat particularly of eclipses.

In every revolution of the moon about the earth, the turns once round upon her axis, and therefore presents the fame face to our view; and her day and night together are as long as our lunar month. As we fee only one fide of the moon, we are therefore invifible to the inhabitants on the oppofite fide, without they take a journey to that fide which is next to us, for which purpose some of them must travel more than 1500 miles.

light on the

As the moon illuminates the earth by a light reflected from the fun, fhe is reciprocally enlightened, but in a much greater degree, by the earth; for the furface is above 13 times greater than that of the moon; and therefore, fuppofing their power of reflecting light to be equal, the earth will reflect 13 times more moon than fhe receives from it. what we call new moon, we shall appear as a full moon to the Lunarians; as it increases in light to us, our's will decreafe to them: in a word, our earth will exhibit to them the fame phases as fhe does to us.

When it is

We have already obferved, that from one half of the moon the earth is never feen; from the middle of the other half, it is always feen over head, turning round almost thirty times as quick as the moon does. To her inhabitants, the earth feems to be the largest body in the universe, about thirteen times as large to them, as she does to us. As the earth turns round it's axis, the feveral continents and islands appear to the Lunarians as fo many fpots, of different forms; by these spots, they may determine the time of the earth's diurnal motion; by these spots, they may, perhaps, measure their time,-they cannot have a better dial.

OF THE SUPERIOR PLANETS.

Mars, Jupiter, Saturn, and the Georgium Sidus, are called fuperior planets, because they are higher in the fyftem, or farther from the center of it, than the earth is,

They exhibit feveral phænomena, which are very different from those of Mercury and Venus ; among other things, they come to our meridian both at noon and midnight, and are never feen croffing the fun's disk.

OF MARS. ♂

Mars is the leaft bright and elegant of all the planets; it's orbit lies between that of the earth and Jupiter, but very diftant from both. He appears of a dufky reddish hue; from the dullnefs of his appearance, many have conjectured that he is encompaffed with a thick cloudy atmo sphere.

Mars, which appears fo inconfiderable in the heavens, is 5,400 miles in diameter, 91,608,956 fquare miles in fuperficial content. It's distance from the fun is 145,014,148 miles. It goes round the fun in 1 year, 321 days, 17 hours, moving at

the rate of 55,287 miles per hour. It revolves round it's axis in 24 hours, 40 minutes; it's orbit is inclined to the ecliptic, at an angle of 1 deg. 52 min.; to an inhabitant in Mars, the fun would appear one-third lefs in diameter than it does to us.

Mars, when in oppofition to the fun, is five times nearer to us than when in conjunction. This has a very vifible effect on the appearance of the planet, caufing him to appear much larger at fome periods than at others.

The axis of this planet is nearly at right angles to it's orbit. The time, therefore, the fun is above the horizon, or the length of the natural day, will almost, in every part, be equal to the night, or the time the fun is below the horizon. There will be very little change or variety of feafons; but places, in different latitudes, will have very different degrees of light and cold, on account of the different inclination of the fun's rays to the horizon.

A fpectator in Mars will rarely, if ever, fee Mercury, except when they fee it paffing over the fun's disk. Venus will appear to him at about the fame diftance from the fun, as Mercury appears

5

The earth will appear about the appears to us. fize of Venus, and never above 48 degrees from the fun; and will be, by turns, a morning and evening ftar to the inhabitants of Mars.

OF JUPITER.

Jupiter is fituated still higher in the system, revolving round the fun, between Mars and Saturn. It is the largest of all the planets, and easily distinguished from them by his peculiar magnitude and light. To the naked eye it appears almost as large as Venus, but not altogether fo bright.

Jupiter revolves round it's axis in 9 hours, 56 minutes; round the fun in 4332 days, 12 hours, 20 minutes, or near 12 years. The difproportion of Jupiter to the earth, in fize, is very great; viewing him in the heavens, we confider him as fmall in magnitude; whereas he is in reality 94,000 miles in diameter, and 25,759,077,600 fquare miles in fuperficial content; his distance from the fun is 494,999,976 miles; he moves at the rate of rather more than 22,101 miles his orbit is inclined to

per hour;

I

the ecliptic, at an angle of 1 deg. 20 min.