THE PLANET SATURN.
377
that of the elongated projectiles which are usually fired froma large piece of modern artillery. For a certain time (viz., forabout 1J years before, and I f years after, a solstice) it wouldfall short of the outer boundary of the rings, just as, for asimilar period, the rings, if seen from the Sun, would entirelysurround the planet. At such a time, therefore, an observerupon the outer part of the ring-system would escape the Solareclipses, w'hile they would he of short duration for one onlyslightly overlapped by the range of the shadow. But at anequinox the eclipses would be of a maximum duration, thelength of which, if we suppose our observer to go round theplanet upon one of the myriad satellites which probably formthe rings, may be easily calculated. It would, in fact, bearthe same ratio to the whole period of his rotation (which wouldbe between seven and fourteen hours) as the width of theshadow, which would then equal the diameter of Saturn’sglobe, would bear to the whole circumference of the orbitdescribed by the observer round the planet.
Oh the other hand, at the time of an equinox, the nightlyrising of the shadow upon the eastern part of the rings, as seenby an observer on the planet near to its equator, would almostcoincide with the setting of the Sun in the west; and it wouldthen sweep rapidly across them until, at midnight, by far thegreater part of the rings would be hidden in its shade. Atplaces in higher latitudes the shadow would not rise so soon,but at midnight it would probably overlie the whole of thatportion of the rings which would otherwise be seen. It wouldof course pass away in the reverse direction before sunrise.
At midnight, in any latitude where it could be seen, theshadow of the planet would be always symmetrically placed inthe centre of the visible portion of the rings.
Near to the time of the Summer Solstice, when the nightswould be shortest, a large portion of the rings would be inshade, even before the setting of the Sun, as seen from placesconsiderably removed from the equator.*
* The above statements are more fully explained, and are illustratedby an elaborate series of diagrams, in Mr. Proctor’s “ Saturn and itsSystem,” to whose valuable work upon the planet we are deeply indebted