Saturn, 1885, Dec. 23, 7h 54m. (10-inch reflector, power 252.)
Divisions in the Outer Ring.—In the middle of the eighteenth century Short, the optician, using one of his excellent reflectors, thought he saw the outer ring divided by several dark lines; but no other observer confirmed his suspicion. In the third decade of the present century Quetelet and Capt. Kater appear to have observed Short’s divisions, but Sir J. Herschel and Struve looked for them in vain. In 1837 Encke fully satisfied himself, by several observations and measurements, as to the objective existence of the divided outer ring. The division was not central, cutting the ring into equal parts, but situated in the inner part of the ring, so that the wider part was outermost. In subsequent years this division has been sometimes seen and placed nearest the outer edge of the ring. Certain observers, provided with ample means, have seen nothing of it; others regard the division as variable. It is sometimes described as a narrow black line; while others refer to it as a faint pencil~like shading, and not a real division at all. One observer occasionally sees it with considerable distinctness at the very same time that another observer, with a more powerful telescope, cannot glimpse it though looking specially for such an appearance! It is difficult to reconcile such discordant experiences, and unsafe to accept results of such a contradictory nature.
The “Crape”-Ring.—A far more certain feature was discovered in the autumn of 1850[44], and one in reference to which there is unanimity of testimony. On Nov. 11 G. P. Bond, in America, and Dawes, in England, on Nov. 25, saw a nebulosity or faint luminous appearance like twilight, fringing the interior margin of the inner ring. Later observations showed this to be occasioned by a transparent ring situated immediately within the inner luminous ring. Dawes considered the new ring to be divided into two parts; but Lassell, with his large reflector, subsequently negatived this supposition. Both limbs of Saturn may be readily perceived through the transparent ring where it crosses the globe of the planet. Some irregularities have been suspected in it at different times by various observers. In 1887 dark condensations were reported to disturb its normal aspect; but these were not seen at many observatories where such features, if real, could hardly have escaped detection.
Saturn, as observed by F. Terby, February 1887.
It is strange to reflect that this transparent ring avoided discovery for so long a period. It forms a feature distinctly to be recognized in relatively small telescopes—in fact, Grover has seen it, where it crosses the globe of Saturn, with only 2 inches of aperture. Yet, though ever on the alert to detect new formations, and exercising constant vigilance in their pursuit, Sir W. Herschel, Schröter, and many others allowed this ring to escape them! There is no reason to suppose that it is variable, and that it was not so plain a century ago as now. It affords another instance of how easily an unknown object may elude recognition, though everyone sees it readily enough when attention is called to it.
In March 1889 a white spot was detected on the rings by Dr. Terby, at Louvain, and it was seen by other observers with comparatively small instruments. The spot was stationary, and placed near the apparent junction of the globe and rings, in the E. ansa. But with large telescopes nothing of this object could be detected: it was shown to be an optical effect.