V1S7BILITY OF STARS'. 61 



Of these Ovid says (Fast. iv. 170), 



" Quse septem dici, sex tamen esse solent." 



One of the daughters of Atlas, Merope, the only one who 

 was wedded to a mortal, was said to have veiled herself 

 for very shame, or even to have wholly disappeared. This 

 is probably the star of about the 7th magnitude, which 

 we call CelaBiio; for Hipparchus, in his commentary on 

 Aratus, observes that on clear moonless nights seven stars 

 may actually be seen. Celseno therefore must have been 

 seen, for Pleione, which is of equal brightness, is too near 

 to Atlas, a star of the 4th magnitude. 



The little star, Alcor, which, according to Triesnecker, is 

 situated in the tail of the Great Bear, at a distance of 

 1 1' 48" from Mizar, is, according to Argelander, of the 5th mag- 

 nitude, but overpowered by the rays of Mizar. It was called 

 by the Arabs, Saidak, " the Test," because, as the Persian 

 astronomer Kazwini 1 * remarks, " It was employed as a test of 



that Attalus, in his description of the Pleiades, should have 

 neglected to notice this oversight on the part of Aratus, as 

 though he regarded the statement as correct." Merope is called 

 the invisible (n ava(pavT]s} in the Catasterisms (XXIII.) ascribed to 

 Eratosthenes. On a supposed connexion between the name 

 of the veiled (the daughter of Atlas) with the geographical 

 myths in the Meropis of Theopompus, as well as with the great 

 Saturnian Continent of Plutarch and the Atlantis, see my 

 Etcamen crit. de I' hist, de la Geographic^ t. i. p. 170. Compare 

 also Ideler, Untersuchungen uberden Ursprung unddie Bedeu- 

 tung der Sternnamen, 1809, p. 145 ; and in reference to astrono- 

 mical determination of place, consult Madler, Untersuch. iiber 

 die Fixstern-Systeme, th. ii. 1848, s. 36 and 166; also Baily 

 in the Mem. of the Astr Soc., vol. xiii. p. 33. 



16 See Ideler, Sternnamen, s. 19 and 25. Arago in manuscript 

 notices of the year 1847, writes as follows . "On observe 

 qu'une lumiere forte fait disparaitre une lumiere faible placee 

 dun* le voisinage. Quelle peut en etre la cause ? II est pos- 

 sible physiolo^iquement que I'ebnmkment communique a la 

 rctiuc par la lumiere forte s'etend uu dt-la des points que la 



