With this opinion as to the tenuity of Nebulæ agrees the absence of all _observed_ motion among their parts; while the extraordinary spiral arrangement of many of them, prove that nevertheless many of them really _have_ motion, and suggests modes of calculating their tenuity, and showing how extreme it is. “It is probable,” said Lord Rosse, in a paper which we ourselves heard him read not long ago, from the chair of the Royal Society, “that in the Nebular systems, motion exists. If we see a system with a distinct spiral arrangement, all analogy leads us to conclude that there has been motion; and that if there has been motion, that motion still continues.”... “Among the Nebulæ,” he says, “there are vast numbers, much too faint to be sketched or measured with any prospect of advantage: the most powerful instruments we possess showing in them nothing of an organised structure, but merely a confused mass of nebulosity, of varying brightness.”[117] The Essayist makes powerful use, moreover, of Sir John Herschell’s celebrated observation of the Magellanic Clouds, lying near the South Pole; exhibiting the coexistence, in a limited compass, and in indiscriminate position, of stars, clusters of stars, nebulæ regular and irregular, and nebular streaks and patches, things different not merely to us, but in themselves: nebulæ, side by side with stars and clusters of stars; nebulous matter resolvable, close to nebulous matter irresolvable;—the last and widest step by which the dimensions of the Universe have been expanded, in the notions of eager speculators, being checked by a completer knowledge, and a sager spirit of speculation.[118] In discussing such matters as these, he finely observes—“It is difficult to make men feel that so much ignorance can lie close to so much knowledge; to make them believe that they have been allowed to discover so much, and yet are not allowed to discover more.”[119]