VARIABLE STABS. 225 



concomitant of redness. There are many red stars: some of 

 them very red as Arcturus and Aldebaran in which, how- 

 ever, no variability has as yet been discovered. And it is 

 also more than doubtful in the case of a star of Cepheus 

 (Xo. 7582 of the catalogue of the British Association), 

 which, on account of its extreme redness, has been called 

 by William Herschel the Garnet Star (1782). 



It would be difficult to indicate the number of periodically 

 variable stars for the reason that the periods already deter- 

 mined are all irregular and uncertain, even if there were no 

 other reasons. The two variable stars of Pegasus, as well as 

 a Hydne, e Aurigse, and a Cassiopeia?, have not the certainty 

 that belongs to Mira Ceti, Algol, and d Cephei. In inserting 

 them, therefore, in a table, much will depend on the degree 

 of certainty we are disposed to be content with. Argelander, 

 as will be seen from the table at the close of this investiga- 

 tion, reckons the number of satisfactorily determined periods 

 at only twenty-four.' 



The phenomenon of variability is found not only both in 

 red, and in some white stars, but also in stars of the most 

 diversified magnitude ; as, for example, in a star of the 1st 

 magnitude, o Orionis ; by Mira Ceti, a Hydree, a Cassiopeiae, 

 and /3 Pegasi, of the 2nd magnitude ; /8 Persei, of the 2' 3rd 

 magnitude ; and in rj AquilaB, and Lyrse, of the 3 -4th mag- 

 nitude. There are also variable stars, and indeed in far- 

 greater numbers, of the 6tli to the 9th magnitude ; such as 



meridian circles of Abo, Helsingfors, and Bonn, I have never 

 seen a Herculis single, which would assuredly have been the 

 case if the companion at its minimum were of the seventh 

 magnitude. I believe the latter to be constant, and of the 

 5th or 5 '6th magnitude. 



D Madler's Table (Astron., s. 435) contains eighteen stars, 

 with widely differing numerical elements. Sir John Herschel 

 enumerates more than forty- five, including those mentioned 

 in the notes. Outlines, 819-826. 



vol. in. 



