“This most glorious object,” as Herschel calls it, “the noble globular cluster ω Centauri, beyond all comparison the richest and largest object of the kind in the heavens,” is evidently quite distinct from κ Crucis and clusters like those described in the last chapter. In form it is circular, and the condensation towards the centre suggests that it is spherical. There are some scattered members of the group lying outside the bright crowded sphere. The stars are also immensely more numerous and more closely packed than in the irregular clusters, their total number being estimated at 10,000, and 6000 have been actually counted on photographs, and all these in a space which looks little larger than that occupied by the sun in the sky. Another striking difference is that, instead of bright and faint stars mingled together, here they are all nearly alike and very minute. Curiously enough, it is found that they belong to two magnitudes, and two only, the thirteenth and fifteenth, and this seems to be a feature of all globular clusters, as well as the form and the dense crowding of the stars. Herschel at first thought the stars in ω Centauri “singularly equal, and distributed with the most exact equality, the condensation being that of a sphere equally filled.” But he immediately adds: “Looking attentively, I retract what is said about the equal scattering and equal sizes of the stars. There are two sizes ... without greater or less, and the larger stars form rings like lace-work on it.” In his later notes he is again doubtful, for he thinks that the effect may be optical, and the larger stars only knots of faint stars; but photography has settled the question in our day. Yet another point of difference between globular and irregular clusters is that the latter often have wisps of nebulosity clinging about them, but globular clusters are entirely free from it. [Illustration: THE STAR-CLUSTER 47 TOUCANI From Sir John Herschel’s drawing] Smaller than ω Centauri, but even more beautiful in the telescope, is the cluster 47 Toucani,[10] which to the unaided eye appears like a fourth-magnitude star near the smaller Cloud of Magellan. The long curve of Grus followed southwards leads to it. Nearly as many stars as in ω Centauri, or about 9500, are here massed into a still smaller space, so the cluster is brighter, and is “compressed to a blaze of light” at the centre. The two sets of stars, which are mingled together throughout, are of thirteenth to fifteenth and of seventeenth magnitudes respectively. Herschel saw the inner denser part rose-coloured while the outer was white, but the present writer could not see this nor find anyone to confirm it to-day, possibly because the refracting telescopes now so often used do not show colour so well as large reflectors like Herschel’s. A double star of 11th magnitude, which is conspicuous in Herschel’s drawing, is doubtless far outside the cluster, and only appears projected against it by perspective.