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Page:Popular Science Monthly Volume 4.djvu/60

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THE POPULAR SCIENCE MONTHLY.

be found in their favor. But, so soon as we regard Saturn's whole globe as in a state of intense heat, and his belt-system as indicating the continual action of forces of enormous activity, we no longer find any difficulty in understanding the possibility of changes such as Sir W. Herschel, Sir G. Airy, the Bonds, and others of like observing skill, have seen with some of the finest reflecting and refracting telescopes ever constructed by man. Nay, we may even go further, and find in solar phenomena certain reasons for believing that Saturn's globe would be subjected to precisely such changes. It appears to have been rendered extremely probable by Secchi and others, that our sun's globe varies in dimensions under the varying influences to which he is subjected. At the height of the spot-period the sun seems to be reduced in diameter, while his colored sierra is deeper, and the red prominences are larger than usual, the reverse holding at the time when the sun has no spots or few. Of course this is not understood as implying a real change in the quantity of solar matter, but only as indicating the varying level at which the solar cloud-envelope lies. We may safely assume that these changes, which correspond to the great spot-period, affect chiefly the spot-zones which lie in the parts of the sun's globe corresponding to our temperate zones; but, for the same reasons that the sun's globe is perfectly spherical so far as measurements can be depended upon, namely, because of its relatively slow rotation—such differences would be too slight to be measurable. Regarding Saturn, then, as we have already been compelled to do for other reasons, as resembling the sun so far that he is in an intensely heated condition, we see grounds for believing that his temperate zones would be exposed to variations of level (cloud-level), which at times might be very considerable, and thus discernible from our earth. For, owing to his rapid rotation on his axis, all such effects would be relatively greater than on a slowly rotating orb like the sun; and in fact we recognize this distinction in the great compression of Saturn's globe. Moreover, if we regard the waxing and waning of the solar spots as associated with the motions of the members of the sun's family, we can well understand that the members of Saturn's family, which lie so much nearer to him compared with his own dimensions, should produce more remarkable effects.[1] But, whether this be so or not, it is certain

  1. ↑ It must not be understood that in thus speaking we countenance the theory that either the planets produce the sun-spots, or the satellites of Saturn effect the remarkable changes we have been dealing with. The real causes of all solar phenomena must be sought in the sun's own globe; and Saturnian phenomena are in the main, we have little doubt, produced by Saturnian action. But even as our moon (probably) exerts an influence on the occurrence of earthquakes and volcanoes, not by her own attraction directly, but by affecting the balance between terrestrial forces, so it may well be that the planets indirectly affect the sun's condition, and that the Saturnian satellites even more effectually act upon Saturn. It would be extremely interesting to inquire whether any connection can be traced between the changes of the Saturnian belts and the motions of his satellites. Or the inquiry might be more readily and quite as effectually applied to Jupiter and his system.