These preliminary attempts shrank into insignificance when Herschel began to "sweep the heavens" with his giant telescopes. In 1786 he presented to the Royal Society a descriptive catalogue of 1,000 nebulæ and clusters, followed, three years later, by a second of as many more; to which he added in 1802 a further gleaning of 500. On the subject of their nature his views underwent a remarkable change. Finding that his potent instruments resolved into stars many nebulous patches in which no signs of such a structure had previously been discernible, he naturally concluded that "resolvability" was merely a question of distance and telescopic power. He was (as he said himself) led on by almost imperceptible degrees from evident clusters, such as the Pleiades, to spots without a trace of stellar formation, the gradations being so well connected as to leave no doubt that all these phenomena were equally stellar. The singular variety of their appearance was thus described by him:-- "I have seen," he says, "double and treble nebulæ variously arranged; large ones with small, seeming attendants; narrow, but much extended lucid nebulæ or bright dashes; some of the shape of a fan, resembling an electric brush, issuing from a lucid point; others of the cometic shape, with a seeming nucleus in the centre, or like cloudy stars surrounded with a nebulous atmosphere; a different sort, again, contain a nebulosity of the milky kind, like that wonderful, inexplicable phenomenon about Theta Orionis; while others shine with a fainter, mottled kind of light, which denotes their being resolvable into stars."[46] "These curious objects" he considered to be "no less than whole sidereal systems,"[47] some of which might "well outvie our Milky Way in grandeur." He admitted, however, a wide diversity in condition as well as compass. The system to which our sun belongs he described as "a very extensive branching congeries of many millions of stars, which probably owes its origin to many remarkably large as well as pretty closely scattered small stars, that may have drawn together the rest."[48] But the continued action of this same "clustering power" would, he supposed, eventually lead to the breaking-up of the original majestic Galaxy into two or three hundred separate groups, already visibly gathering. Such minor nebulæ, due to the "decay" of other "branching nebulæ" similar to our own, he recognised by the score, lying, as it were, stratified in certain quarters of the sky. "One of these nebulous beds," he informs us, "is so rich that in passing through a section of it, in the time of only thirty-six minutes, I detected no less than thirty-one nebulæ, all distinctly visible upon a fine blue sky." The stratum of Coma Berenices he judged to be the nearest to our system of such layers; nor did the marked aggregation of nebulæ towards both poles of the circle of the Milky Way escape his notice.