48 SPECIAL RESULTS IN THE URANOLOGICAL 



are not visible to the naked eye in persons of ordinary powers 

 of vision. The group of the Pleiades consists of a star of 

 the 3rd magnitude, Alcyone; two of the 4th magnitude, 

 Electra and Atlas ; three of the 5th, Merope, Maia, and 

 Taygeta ; two between the 6th and 7th, Pleione and Celseno ; 

 one between the 7th and 8th, Asterope ; and several very 

 small telescopic stars. I employ the present denominations 

 and oi-'ler of magnitudes, for among the ancients some of these 

 names were assigned to other stars. It was only the six first- 

 named stars, of the 3rd, 4th, and 5th magnitudes respectively, 

 that could be easily seen. ( 103 ) Ovid says (Past. iv. 170) : 

 " Quse septem dici, sex tamen esse solent." It was supposed 

 that one of the daughters of Atlas, Merope, the only one 

 who had married a mortal, remained veiled through bashful- 

 ness, or even that she had entirely disappeared. She was 

 probably the star of almost the 7th magnitude, which we 

 now call Celseno ; for Hipparchus remarks, in the commen- 

 tary to Aratus, that in clear moonless nights seven stars 

 could really be perceived. It was then Celseno which was 

 seen as the seventh Pleiad ; Pleione, which is of equal 

 brightness, being too near Atlas (a star of the 4th magni- 

 tude) to be distinguished. 



The small star Alcor (which, according to Priesnecker, is 

 at a distance of 11' 48" from Mizar, in the tail of the Great 

 Bear) is, according to Argelander, of the 5th magnitude, but 

 overpowered by the brightness of Mizar. It was called by 

 the Arabs " Saidak," " the tester ;" because it was the cus- 

 tom, as the Persian astronomer Kazwini( 104 ) informs us, 

 " to test a man's power of sight by it." Notwithstanding 

 the low altitude of the constellation of the Great Bear within 

 the tropics, I have seen Alcor with the naked eye with 



