GrORE — On Known Variable Stars. 



167 



a period of about 331 days. Schonfeld gives the following formula 

 for the time of maximum : — 



/ 360° 

 1866. 11" 25^-4: + 331-3363 E + 10''-48 sin ( —— E + 282° 45' 



/45° \ 



( — E-f31°15'j 



+ 18'*-16sin[ — E-f 31°15' 



/450 

 + 33'^-90 sin I — E + 70° 5' 



+ 65'*-31 sin ( -^ E + 179° 48' 



Argelander thought that the variations of brilliancy indicate a 

 40-year period. According to the same eminent authority, the mean 

 brightness of Mira at maximum is IJ steps brighter than y Ceti. 

 Heis finds it 2 steps brighter ; and taking the brightness of y Ceti as 

 31, he finds the average brilliancy of Mira at maximum, between 

 1840 and 1858, as 33-2 steps. 



The mean duration of visibility to the naked eye is, according to 

 Heis, 4 months ; the interval from first visibility to maximum being 

 at the mean 42' 7 days, and from maximum to disappearance (to the 

 naked eye) 73*7 days. 



At minimum, Schmidt gives the magnitude 9*5 m. ; but Schonfeld 

 states that he has never seen it fainter than the companion (89°, 116", 

 1831), or 9-1 m., and usually somewhat brighter. Heis states (an. 

 1741) that at the maximum of 1868 (Nov. 7) Mira was fainter than 

 he had seen it for 27 years — not brighter than A Ceti. At the maxi- 

 mum of 1799 it was thought to be not little inferior to Aldebaran. 



The following table shows the observed maxima of Mira Ceti since 

 1840:— 



Obseeved Maxima of Miea Ceti. 



Year. 



Date 



of 



Maximum. 



Brightness. 



Authority. 



Remarks. 



1840. 



Sept. 29 



Steps. 

 32-0 



Heis. 





1841. 



Aug. 27 



32-0 



» 





1842. 



July 24 



36-5 



)) 





1845. 



Feb. 27 





Schmidt. 





1846. 



Fet. 4 





)) 





1846. 



Dec. 20 



41-0 



Heis. 





1847. 



Jan. 3 





Schmidt. 





Z2 



