160 SPECIAL RESULTS IN THE URANOLOGICAL PORTION 



but as yet this investigation is still subject to many uncer- 

 tainties in the comparison of long and short periods. Of 

 #Lyrse, from 1700 to 1800 periods have been observed; of 

 Mira Ceti, 279 ; of x Cygni, only 145. 



The question which has been asked, whether stars which 

 have long shewn themselves variable in regular periods 

 cease to be so, would appear to require to be answered in 

 the negative. If among the persistently varying stars there 

 are some which shew sometimes a very great and sometimes 

 a very slight degree of variability (for example, variabilis 

 Scuti), there would also appear to be others whose variability 

 is at certain times so small, that, with our limited means, we 

 cannot detect it. The star variabilis Coronse bor. (No. 

 5236 in the British Association Catalogue), of ' which 

 Pigott recognised the variability, and which he observed for 

 some time, belongs to this class. In the winter 1795- 

 3 7 9 6, this star was quite invisible : subsequently it reappeared, 

 and its alterations of light were observed by Koch. Harding 

 and Westphal, in 1817, found its brightness almost constant; 

 but, in 1824, Olbers was again able to observe its change. 

 Afterwards the constancy of light returned, and from August 

 1843 to September 1845 was observed by Argelander. At 

 the end of the month of September, 1845, a fresh decrease 

 began to take place. In October, the star was no longer 

 visible in the Comet- seeker : it reappeared in February 1846, 

 and in the beginning of June it had again attained its usual 

 magnitude (the 6th), which it has since retained, if we omit 

 the consideration of small and not very well assured fluc- 

 tuations. To this perplexing class of stars the one called 

 variabilis Aquarii also belongs, as does perhaps Janson's and 

 Kepler's star in Cygnus, which appeared in 1600, and which 

 we have already noticed among " New stars/' 



