telescope eight inches and a half in aperture, found that 'the dark ring could not be overlooked for an instant.' But while this increase in the distinctness of the dark ring was to be expected, from the mere fact that the ring was discovered under relatively unfavourable conditions, yet the fact that Saturn was thus found to have an appendage of a remarkable character, perfectly obvious even with moderate telescopic power, was manifestly most surprising. The planet had been studied for nearly two centuries with telescopes exceeding in power those with which the dark ring was now perceived. Some among these telescopes were not only of great power, but employed by observers of the utmost skill. The elder Herschel had for a quarter of a century studied Saturn with his great reflectors eighteen inches in aperture, and had at times turned on the planet his monstrous (though not mighty) four-feet mirror. Schröter had examined the dark space within the inner bright ring for the special purpose of determining whether the ring-system is really disconnected from the globe. He had used a mirror nineteen inches in aperture, and he had observed that the dark space seen on either side of Saturn inside the ring-system not only appeared dark, but actually darker than the surrounding sky. This was presumably (though not quite certainly) an effect of contrast only, the dark space being bounded all round by bright surfaces. If real, the phenomenon signified that whereas the space outside the ring, where the satellites of the planet travel, was occupied by some sort of cosmical dust, the space within the ring-system was, as it were, swept and garnished, as though all the scattered matter which might otherwise have occupied that region had been either attracted to the body of the planet or to the rings.[36] But manifestly the observation was entirely inconsistent with the supposition that there existed in Schröter's time a dark or dusky ring within the bright system. Again, the elder Struve made the most careful measurement of the whole of the ring-system in 1826, when the system was as well placed for observation as in 1856 (or, in other words, as well placed as it can possibly be); but though he used a telescope nine inches and a half in aperture, and though his attention was specially attracted to the inner edge of the inner bright ring (_which seemed to him indistinct_), he did not detect the dark ring. Yet we have seen that in 1851, under much less favourable conditions, a less practised observer, using a telescope of less aperture, found that the dark ring could not be overlooked for an instant. It is manifest that all these considerations point to the conclusion that the dark ring is a new formation, or, at the least, that it has changed notably in condition during the present century.