Clusters and Nebula. 459 



CLUSTERS AND NEBULA.— SOUTHERN OBJECTS.— 

 DOUBLE STARS.— OCCULTATION. 



BY THE EEV. T. W. WEBB, A.M., F.E.A.S. 



If we suppose a line drawn from Arcturus to a Opliiuchi, and 

 from near its centre drop a perpendicular to it for some dis- 

 tance, the latter will hit a 2 mag. star, the brightest in a 

 considerable area, a Serpentis, which may be also identified 

 from its lying in a straight line between two 3 mag. attend- 

 ants, the one n p being o (which is double, No. 26 of our list, 

 Int. Obs. ii.j 56), the other s f (which is nearer a) being e. 

 From this last star we must run out a line at something less 

 than a right angle — say 80° — with that joining e and 8, and of 

 about equal length ; if we then sweep over the region where it 

 ends, we shall find a 5 mag. star, 5 Serpentis, which should be 

 visible to a keen sight, but will at any rate be conspicuous with 

 slight optical aid : just n p, the finder will show us a patch of 

 haze, and the telescope will reveal — 



44. The Great Cluster in Libra. Gen. Cat. 4083— M 5. 

 Smyth calls this a most beautiful cluster of minute stars, greatly 

 compressed in the centre, with outliers in all directions. In his 

 achromatic of 5^ inch aperture it was a superb object, with a 

 bright central blaze, exceeding even M 3 (No. 41 in our last 

 number) in concentration. The progress of optical power is 

 well illustrated by the fact that M., the discoverer, said of it, 

 in 1764, " je me suis assure qu'elle ne contient aucune etoile," 

 and J£ with the 40f. reflector, in 1791, counted about 200 in it, 

 though they were unclistinguishable from compression in the 

 centre. H. with less aperture, but finer definition, describes it 

 as " a most magnificent, excessively compressed cluster of a 

 globular character. Stars 11 — 15 mag. Diam. in R.A.=10 sec. 

 of time : the more condensed part projected on [seen through ?] 

 a loose irregular ground of stars. The condensation is pro- 

 gressive up to the centre, where the stars run together into a 

 blaze, or like a snowball ; the scattered stars occupy nearly 

 the whole field. The neighbourhood is poor in stars. " He 

 has also given a beautiful figure, well exhibiting the general 

 character, especially as to the varying sizes of the stars. 

 With my 9£ inch speculum I found it a very bright and beau- 

 tiful object, the central body of minute stars being barely 

 resolved, while many larger ones are scattered irregularly 

 around and across, or throughout, the glittering accumula- 

 tion. I noticed, however, some features which do not appear 

 either in the description or drawing of H. The brightest part 

 of the condensed mass lies decidedly n p its general centre of 



