The Planet Saturn. 49 



THE PLANET SATURN. 



(continued.) 

 BY THE EEV. T. W. WEBB, A.M., F.E.A.S. 



Befoee we proceed to review tlie anomalies exhibited during 

 the lateral presentation of the ring-system, we must take some 

 notice of an idea to which Secchi was conducted by the singu- 

 lar disagreement of the measures which he obtained of it in 

 its more open position. This eminent observer was induced 

 by % II. 's suspicious as to the permanency of the ring, and 

 the remarkable differences between the results of the first 

 astronomers — Lassell, Encke, and Galle having given upwards 

 of 1"'5 more than Bessel to the outer diameter of the whole — 

 to use the micrometer largely himself. He found his values on 

 any given evening very accordant among themselves, their 

 discrepancies ranging within 0"*3 ; on different ones perplex- 

 ingly the reverse, much more so than in the case of double 

 stars; for instance, as the extremes of sixteen nights, 1855, 

 Dec. 15, 41"-443; Dec. 27, 40"*412. A comparison of these 

 variations, which he found in some respects corroborated by 

 the observations of Lassell, Main, and De la Rue, led him to 

 reflect whether the ring, as a whole, might be subject to 

 periodical dilatation, or might be elliptical in form, with a 

 rotation sometimes presenting to us its longer, sometimes its 

 shorter axis. Of these two suppositions he thought the latter 

 the more probable, suggesting a period of about 14h/238; but 

 on the whole considered that there might be not merely 

 ellipticity and rotation, but some actual variation in diameter ; 

 hence concluding that there is no reason to fear, with S II., a 

 progressive alteration and final destruction of this " beautiful 

 accessory " to the planet. 



These last expressions of Secchi refer to a singular and 

 impressive speculation of 2 II., who, from a careful comparison 

 of the ancient drawings and measurements, such as they were, 

 of the ansse and the included space with more modern values, 

 had been induced to believe that the ring-system, especially 

 the inner edge of B, was in a state of such perceptible and 

 rapid approximation to the planet that its ultimate disintegra- 

 tion was now not only a mere question of time, but, as it 

 would seem, of a comparatively short interval. More recently, 

 however, the improbability of this curious hypothesis has been 

 shown by the measurements of Main (then Senior Assistant at 

 Greenwich, now Badcliffe Observer at Oxford) ; and the ideas 

 of both 2 II. and Secchi, though too interesting to be passed 

 unnoticed in a recital like the present, have been so strongly 



VOL. 5. NO. I. E 



