THE PHASES OF THE PLANET SATURN.

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The planets move in orbits more or less elliptical, although not differinggreatly from circles. These orbits are inclined to the plane of that of theearth by a greater or less difference, as we have already stated ; and the planetsthemselves have their axes of rotation inclined to the planes of their orbits,respectively, in different angles. This latter circumstance will be explained inreference to each planet, at the close of our views of the system.

The axis of rotation of the planet Saturn is inclined to his orbit about sixtydegrees; and the plane of his ring is at right angles with, or ninety degreesfrom, his axis ; so that it has an inclination to the plane of the earth’s orbitof nearly thirty degrees.

Now, the axis of Saturn , and, consequently, that of his rings, constantlykeeps the same direction during the entire revolution of the planet about thesun; and as the performance of this revolution occupies nearly thirty years, thesun shines for about fifteen years together on one side of his ring, and then forfifteen years on the other side. But twice, in the thirty years of his revolution,there must be an instant when neither side of the ring is enlightened—whenonly the outer edge of the ring is presented to the sun; that is, when the sunceases to shine on one side, and is just about to shine on the other.

The lower figure of the scene, shewing the planet in eight points of itsorbit, will illustrate this. The sun is seen in the centre ; and next, imme-diately round it, is shewn the earth in eight points of her orbit, correspondingwith, and opposite to, the eight positions of Saturn . When the planet Saturn is at that point of his orbit marked a, the earth sees the body of the planet,with the edge of its ring crossing it like a bright line, as it is separately shewnat the small figure a of the side columns of figures. When Saturn hasadvanced to the point b of his orbit, the sun shines on the under side of hisring, and the earth sees the planet and the ring, as shewn at b of the smallfigures. When the planet has arrived at c, the sun still enlightens the underside of the ring, and it appears to the earth, as shewn at c, the ellipticalfigure of the ring being wider than it W’as in any part of its orbit from thepoint a. When it has arrived at the point d, the sun still shines upon theunder side of the rings, and it appears as at d. When it has travelled on to thepoint e, it is again in one of those positions in which the sun does not shine oneither side of the ring; as it was at a, to which point in the orbit it is opposite.In this position the ring is again seen as a bright line crossing the body of theplanet, as shewn in the small figure at e. At the point f, in its orbit, the planetpresents nearly the appearance it did when at the opposite point at b, as to thequantity of its ellipticity ; but the sun now shines upon the upper side of thering; the appearance of the planet and ring is then as shewn at the small figuref. When arrived at g, the sun is then shining more fully on the upper side ofthe ring; it is then at its other point of greatest ellipticity, the first being atits opposite point c, and appears as at g of the small figures. At h, the suncontinues to shine on the upper surface of the ring, but the ellipticity isreduced ; it appears as in the small figure at h. At a, the planet has completedits revolution through its entire orbit, and has exhibited, in its phases, all thegradations of ellipticity between the straight lines at the opposite points at a