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THE PLANET SATURN.

Iapetus, the fifth satellite in order of discovery, but thefurthest from Saturn , shows a considerable variability in itslight. This was especially remarked by J. 1). Cassini, whodiscovered it, and subsequently by Sir Wm. Herschel, andmay be supposed to indicate an axial rotation, or a variation inthe reflective power of different portions of its surface, similarto that which has been suspected in the case of some of thesatellites of Jupiter.

And here we must leave this most fascinating system. Itis sad that we know so little of its beauties and its mysteries.We look forward, however, with the utmost interest and hope-fulness to the observations of the rings that may be madeduring the next few years, while they will appear to be verywidely opened out. Since they were last so seen, telescopes ofgreatly improved power and precision have been constructedin tbe observatories of Washington, Vienna, Ealing, and else-where. We know not how soon we may be startled by somesurprising discovery, some new revelation, which shall show uswhy Saturn is girdled with rings such as no other planetpossesses. We do not in the least anticipate the occurrenceof any violent catastrophe by which the rings will be suddenlydestroyed, but we may ere long be taught whether they areto be considered absolutely permanent, or whether they areundergoing some slow process of change, which, in course oftime, may aggregate their constituent parts to form additionalsatellites of the planet, or gradually draw them down upon it,to add a slight increase to its bulk.

The Saturnian system seems to be unique; let us hope thatits teaching with regard to itself, and the Solar System as awhole, may also, in course of time, be unique in interest andinstruction.