Clusters and Nebula?. • 117 



were no fewer than 258,000 stars. Carrying this view into 

 adjoining regions, words and figures necessarily fail, for the 

 powers of mind falter in such vast and awful conceptions." 



We will now take the most celebrated and best known of all 

 the globular clusters, and certainly the most beautiful in the 

 smaller class of instruments. It is — 



20. The Great Cluster in Hercules, or 13 M. To find it, 

 we nrast run a line from Wega to Gemma (a Coronal) . This will 

 first fall upon three stars near together, which, reckoning from 

 Wega, are p Herculis, 4 mag. (No. 39 of our Double Stars ; 

 Intellectual Observer, Sept., 1862, p. 136), 69 Here, 4 mag., 

 and 7r Here, 3 mag. The line will then pass, at somewhere 

 about half its length, midway between two 3 mag. stars lying 

 at some distance above and below it, 77 Herculis above, £ below. 

 Between these two again, but about J-rd of the way from rj, lies 

 our cluster. Halley, who discovered it in 1714, says, ' ' This 

 is but a little patch, but it shows itself to the naked eye when 

 the sky is serene and the moon absent." The finder will, ot 

 course, catch it at once ; and in small instruments, and with 

 low powers, it will appear as a very beautiful bright nebula, 

 while its resolution will be complete in proportion to the aper- 

 ture and magnifier employed. Messier satisfied himself, with 

 a power of 60 in a 4 foot Newtonian, that it contained no 

 star ! y is said by Arago to have counted — he must have 

 meant, guessed at — more than 14,000 with the 40 foot tele- 

 scope. Its starry nature was very evident with my 3jq- inches, 

 and with my present aperture its resolution under a high 

 power, though still nebulous and requiring more light, is very 

 fine. Sir J. Herschel describes it as "very gradually much 

 brighter in the middle ; stars 10 to 15 mag., of which there 

 must be thousands ; does not come up to a nucleus ; has hairy- 

 looking curvilinear branches :" and, in another observation, 

 " irregularly round, with scattered stars in streaky masses and 

 lines; excessively condensed to a perfect blaze; stars 11 to 

 20 mag." (the extreme of his scale), " 7 or 8' diameter. Most 

 magnificent object. The state of compression indicates a 

 globular form not much denser at the centre." The curvilinear 

 arrangement here spoken of is curious. We have referred 

 elsewhere to its existence as pointed out by Secchi in the 

 galaxy; and the Earl of Rosse, to whose optical power even 

 the central condensation has given way, observes, with refer- 

 ence to the inquiry whether the spiral form perceived in certain 

 nebulee does not indicate a structure quite different from that 

 of any known cluster, that in the exterior stars of some 

 clusters, of which he gives 13 M. as an example, (c there 

 appears to be a tendency to an arrangement in curved branches, 

 which cannot well be unreal or accidental." So that we seem 



