VARIABLE STARS. 171 



have long appeared to be variable in regular periods ever 

 cease to be so, must apparently be answered in the nega- 

 tive. As among the constantly variable stars there are 

 some which at one time exhibit a very great, and at anoth- 

 er a very small degree of variability (as, for instance, vari- 

 abilis Scuti), so, it seems, there are. also others whose vari- 

 ability is at certain times so very slight, that, with our lim- 

 ited means, we are unable to detect it. To such belongs 

 variabilis Corona? bor. (No. 5236 in the Catalogue of the 

 British Association), recognized as variable by Pigott, who 

 observed it for a considerable time. In the winter of 1795-6 

 this star became totally invisible ; subsequently it again 

 appeared, and the variations of its light were observed by 

 Koch. In 1817, Harding and Westphal found that its bright- 

 ness was nearly constant, while in 1824 Olbers was again 

 enabled to perceive a variation in its luminosity. Its con- 

 stancy now again returned, and from August, 1843, to Sep- 

 tember, 1845, was established by Argelander. At the end 

 of September, a fresh diminution of its light commenced. 

 By October, the star was no longer visible in the comet-seek- 

 er ; but it appeared again in February, 1846, and by the be- 

 ginning of June had reached its usual magnitude (the sixth). 

 Since then it has maintained this magnitude, if we overlook 

 some small fluctuations whose very existence has not been 

 established with certainty. To this enigmatical class of stars 

 belong also variabilis Aquarii, and probably Janson and Kep- 

 ler's star in Cygnus of 1600, which we have already men- 

 tioned among the new stars. 



