CLUSTERS OF STARS 191 



I will content myself with naming the following among the 

 isolated systems of clusters and swarms of stars. 



The Pleiades: doubtless known to the rudest nations 

 from the earliest times ; the mariner's stars Pleias, OTTO TOV 

 jrXfti/, (from TrXetv, to sail,) according to the etymology of the 

 old scholiast of Aratus, who is probably more correct than 

 those modern writers, who would derive the name from 

 irXeor, plenty. The navigation of the Mediterranean lasted 

 from May to the beginning of November, from the early 

 rising to the early setting of the Pleiades. 



Praesepe in Cancer: according to Pliny, nubecula quam 

 Prcesepia vacant inter Asellos, a ve<j>&iov of the Pseudo-Eratos- 

 thenes. 



The cluster of stars on the sword-hilt of Perseus, frequently 

 mentioned by Greek astronomers. 



Coma Berenices, like the three former, visible to the naked eye. 



A cluster of stars near Arcturus (No. 1663), telescopic: 

 R. A. 13h. 34m. 12s., N. Decl. 29 14'; more than a thousand 

 stars from the 10th to the 12th magnitude. 



Cluster of stars between 77 and Herculis, visible to the 

 naked eye in clear nights. A magnificent object in the 

 telescope (No. 1968), with a singular radiating margin; 

 R. A. 16h. 35m. 37s., N. Decl. 36 47'; first described by 

 Halleyin 1714. 



A cluster of stars near a> Centauri; described by Halley 

 as early as 1677; appearing to the naked eye as a round 

 cometic object, almost as bright as a star of the 4th or 

 5th magnitude; in powerful instruments it appears com- 

 posed of countless stars of the 13th to the 15th magnitude, 

 crowded together and most dense towards the centre; 

 R. A. 13h. 16m. 38s., S. Decl. 46 35'; No. 3504 in Sir John 

 Herschel's catalogue of the clusters of the southern hemisphere, 

 15' in diameter. (Observations at the Cape, pp. 21, 105; 

 Outlines of Astr., p. 595.) 



