THE PLANET SATURN.
359
Under intermediate conditions the circular form of the ringswould he seen, by the effect of perspective, as a more or lessoval ellipse, according to the angle at which their plane mighthe inclined to the direction of the observer’s gaze ; the major, orlarger, axis of the ellipse always remaining constant in magni-tude ; the minor axis gradually increasing, or diminishing.
Now observation shows that the plane of the rings is inclinedat an angle of about 27° to the plane of Saturn ’s orbit, and
Orbit
1891 -
that it always retains a parallel position in space, while Saturn travels round the Sun with a speed barely one-third of that ofthe Earth in its long journey of nearly 29i years’ duration. Therings, if seen from the Sun, would therefore present in succes-
* This diagram is partly copied, by Mr. Bentley’s kind permission, fromone in the English edition of “ The Heavens,” by Guillemin. The irregu-larity in the intervals indicated in it, e.g., 1885—1891, 1891—1899, betweeneach of which Saturn describes the same angle of 90° around the Sun , ispartly due to the different months in each year (see page 360, lines 4-8)to which the positions of the planet correspond, but principally to its un-equal velocity in its orbit ; its maximum speed occurring when it is inperihelion, in the year 1885 ; its minimum -when in aphelion, in the year1900.