full moon. As fhe paffes through the other half of her orbit, from E by F G, and H to A again, fhe puts on the fame faces as before, but in a contrary order or position.

As the moon, by reflected light from the fun, illuminates the earth, fo the earth does more than repay her kindness, in enlightening the furface of the moon, by the fun's reflex light, which fhe diffuses more abundantly upon the moon, than the moon does upon us; for the furface of the earth is confiderably greater than that of the moon, and confequently if both bodies reflect light in proportion to their fize, the earth will reflect much more light upon the moon, than it receives from it.

In new moon, the illuminated fide of the earth is fully turned towards the moon, and the Lunarians will have a full earth, as we, in a fimilar pofition, have a full moon. And from thence arifes that dim light which is obferved in the old and new moons, whereby, befides the bright and fhining horns, we can perceive the rest of her body behind them, though but dark and obfcure. Now when the moon comes to be in oppofition to the fun, the earth, feen from the moon, will appear in conjunction with him, and it's dark

fide will be turned towards the moon, in which pofition the earth will be invifible to the Lunarians; after this, the earth will appear to them as a crefcent. In a word, the earth exhibits the fame appearance to the inhabitants of the moon,

that the moon does to us.

The moon turns about it's own axis in the same time that it moves round the earth; it is on this account that fhe always prefents the fame face to us or by this motion round her axis, the turas juft fo much of her furface conftantly towards us, as by her motion about the earth would be turned from us.

This motion about the axis is equable and uniform, but that about the earth is unequal and irregular, as being performed in an ellipfis, confequently the fame precife part of the moon's furface can never be fhewn conftantly to the earth; which is confirmed by a telescope, by which we often obferve a little fegment on the eastern and western limb, appear and disappear by turns, as if her body librated to and fro; this phænomenon is called the moon's libration. The lunar motions are fubject to several other irregu larities, which are fully difcuffed in the larger works on aftronomy.

OF ECLIPSES.

Those phænomena that are termed eclipfes, were in former ages beheld with terror and amazement, and looked upon as prodigies that portended calamity and mifery to mankind. These fears, and the erroneous opinions which produced them, had their source in the hieroglyphical language of the firft inhabitants of the earth. We do not, however, imagine that even the most ancient of these knew any more of the laws and motions of the heavenly bodies, than what could be discovered from immediate fight; or that they knew enough of the lunar fyftem to calculate an eclipfe, or even that they ever attempted it.

The word ECLIPSE is derived from the Greek, and fignifies dereliction, a fainting away, or fwooning. Now as the moon falls into the fhadow of the earth, and is deprived of the fun's enlivening rays, at the time of her greatest brightnefs, and even appears pale and languid before her obfcuration, lunar eclipfes were called LUNE LABORES, the ftruggles or labours of the moon ; to relieve her from thefe imagined diftreffes, fuperftition adopted methods as impotent as they were abfurd.

When

When the moon, by paffing between us and the fun, deprived the earth of it's light and heat, the fun was thought to turn away his face, as if in abhorrence of the crimes of mankind, and to threaten everlasting night and deftruction to the world. But thanks to the advancement of science, which, while it has delivered us from the foolish fears and idle apprehenfions of the ancients, leaves us in poffeffion of their reprefentative knowledge, enables us to explain the appearances on which it was founded, and points out their perverfion and abuse of it.

Any opake body that is exposed to the light of the fun, will caft a fhadow behind it. This fhadow is a space deprived of light, into which if another body comes, it cannot be feen for want of light; the body thus falling within the fhadow, is faid to be ECLIPSED.

Hence there must be three bodies concerned in an eclipfe; 1. the luminous body; 2. the opake body, that cafts the fhadow; and, 3. the body involved in the shadow.

OF

OF ECLIPSES OF THE MOON.

As the earth is an opake body, enlightened by the fun, it will caft a fhadow towards thofe parts that are oppofite to the fun, and the axis of this fhadow will always be in the plane of the ecliptic, because both the fun and the earth are always there.

The fun and the carth are both spherical bodies; if they were, therefore, of an equal fize, the shadow of the earth would be cylindrical, as in fig. 5, plate IX. and would continue of the fame breadth at all diftances from the earth, and would confequently extend to an infinite distance, fo that Mars, Jupiter, or Saturn, might be eclipfed by it; but as these planets are never eclipsed by the earth, this is not the shape of the fhadow, and confequently the earth is not equal in fize to the fun.

If the fun were less than the earth, the shadow would be wider, the farther it was from the earth, fee fig. 6, plate IX. and would therefore reach to the orbits of Jupiter and Saturn, and eclipfe any of thefe planets when the earth came between the fun and them; but the earth never eclipfes them, therefore this is not the fhape of it's fhadow,