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Page:Popular Science Monthly Volume 13.djvu/601

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In the limited number of cases which one system is capable of affording, we cannot expect to see the last struggles of a satellite to maintain its planetary structure when moving in a very close proximity to its primary. But the wonderful annular girdle around Saturn shows evidence not only of a great conflict for planetary existence in past times, but even of lesser ones, on an extensive scale, at the present day. From the investigations which I have published on the subject in the Philosophical Magazine, it appears that in the zone of the outer ring a satellite as dense as Saturn could not hold its parts together, and that one twice as dense could not move in safety in the central zone of the inner ring. If, in treating on stability in small orbits, I have generally supposed the satellite fluid in my papers on the subject, it was because they were chiefly intended to decide whether or not it was possible for the matter of the rings to unite and form two secondary planets.

The long-cherished idea that the rings are two integral solid masses is now generally abandoned. For such a constitution the nearer ring would require to be composed of materials over 200 times as strong as wrought-iron, in order to escape rupture; but even this condition could not avert destruction from other dangers to which it is exposed. From the estimates and observations of Bond, as well as from the theoretical researches of Pierce and Maxwell, it appears certain that the innumerable parts of Saturn's ring cannot be all connected together, in a rigid or permanent manner, but must move independently around the great planet. But, while affording much valuable negative information on the subject, the investigations of these eminent mathematicians do not show how the floating matter eternally circulating in these extensive zones is kept from concentrating into two satellites by the impulse of gravity. The cause which prevents this aggregation is to be found in the proximity of Saturn, whose tidal action either annuls gravity or reduces it so much in two directions as to render a planetary structure unstable; and though an incipient satellite may constantly grow by appropriating the floating matter around it, yet it must fall to pieces before it has attained any considerable magnitude. The state of the rings thus depends not on accidental but on inevitable circumstances; and, with this basis for our inquiries on the subject, we may arrive at very important information in regard to the past and the future condition of worlds.



THERE can be no doubt that, as each person now living has had a father and mother, grandfathers and grandmothers, and so on, every one really comes of as old a family as every one else. Moreover, every living eldest son is the heir male of either the senior or a junior