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THE BEAUTY OF THE HEAVENS.

the planet, and of its rings, we refer to the upper and middle figure of thescene. The outer band is the outer ring; the narrow black circular line shewsthe intervening space between the outer and inner rings; the broader space,next to this line, represents the inner ring. The broad black space, next withinthe broad ring, shews the distance between the inner ring and the body of theplanet. The globe, which occupies the centre of the figure, represents the bodyof the planet itself. It will be understood that this figure shews the planet, asit were, in plan, or as it would appear to an observer situated directly over it,and looking down upon it and its ring, in a direction at right angles to theplane of the ring.

The lower figure of the scene represents the planet in several positions, orpoints, of its orbit. The view taken of it is such as would be visible to anobserver situated at a considerable distance beyond its orbit, and elevatedsomewhat above its plane ; the orbit, which is, really, nearly of a circular form,would appear from such a point of view elliptical, as in the figure. Knowing, aswe do, that the figure of Saturn’s ring also is, really, circular, we are now toconsider why it appears to us elliptical, and why of different degrees ofellipticity.

As we understand what is meant by the inclination of one plane to another,in quantities that are measurable, so we can easily comprehend that lines aresometimes inclined, in the same manner, to each other, or to planes with whichthey are connected; thus, the axle of a wheel which rolls on the ground is aline which lies parallel to the ground; its inclination to the plane is nothing.In a child’s toy, composed of a disc of card, having a stem passing through itat right angles to its face, and on which it is made to spin, the stem, or the axison which it rotates, is at right angles to the plane, or table, on which it moves;it is inclined from that plane ninety degrees. The child spins the toy hecalls a top, and at the commencement of its performance, while it rotates on itsaxis, it also makes wide circuits on the ground, during which its axis is, atfirst, considerably inclined to the plane on which it is moving ; the top’s widerevolutions gradually subside, and, at the same time, the inclination of its axisalso diminishes, the angle it makes with the ground becomes less, until atlength, although the top continues to rotate, it ceases to make any revolutions,and the axis is then in the position we term upright; it makes an angle of ninetydegrees with the ground ; it is not inclined to the plane of the ground at all.Now the axes of rotation of the planets are all of them inclined to the planes oftheir orbits, in a greater or less quantity, and the inclination of a planet’s axis ofrotation is constant ; i. e. it preserves the same inclination in every part of itsorbit. We may take the earth as an example of this ; the north pole, and, con-sequently, the axis on which the earth makes its rotation, points always to thenorth, through its entire orbit. It revolves about the sun nearly in a circle,through a course of 300 millions of miles, the axis retaining the same direc-tion, viz. north and south, through the entire orbit, and this permanently.

We can now consider the planetary motions in further detail than we did inour general view; certain peculiarities of each can now be explained, whichbefore would have been inconsistent with the necessary perspicuity.