238 COSMOS. 



case of this star the disturbance of its period may be expressed 

 by a formula of sines. 



(8) J Cephei, R. A. 335 54', Decl. + 57 39'. Of all the 

 known variable stars, this exhibits in every respect the greatest 

 regularity. The period of 5d. 8h. 47m. 39s. is given by 

 all the observations from 1784 to the present day, allowing 

 for errors of observation, which will account for all the slight 

 differences exhibited in the course of the alternations of 

 light. This star is in its minimum three-quarters of a 

 gradation brighter than t ; in its maximum, it resembles i of 

 the same constellation (Cepheus). It takes Id. 15h. to pass 

 from the former to the latter ; but, on the other hand, more 

 than double that time, viz. 3d. 18h. to change again to its 

 minimum : during eight hours of the latter period, however, 

 it scarcely changes at all, and very inconsiderably for a whole 

 day. 



(9) aHerculis, R. A. 256 57', Decl. + 14 34'; an ex- 

 tremely red double star, the variation of whose light is in every 

 respect very irregular. Frequently, its light scarcely changes 

 for months together ; at other times, in the maximum, it is 

 nearly five gradations brighter than in the minimum; 

 consequently, the period also is still very uncertain. The dis- 

 coverer of the star's variation had assumed it to be sixty-three 

 days. I at first set it down at ninety-five, until a careful 

 reduction of all my observations made during seven years at 

 length gave me the period assigned in the text. Heis believes 

 that he can represent all the observations by assuming a 

 period of 184-9 days, with two maxima and two minima. 



(10) CoronaB R, R. A. 235 36', Decl. + 28 37'. This 

 star is variable only at times : the period set down has been 

 calculated by Koch from his own observations, which unfortu- 

 nately have been lost. 



(11) Scuti R, R. A. 279 52', Decl. 5 51'. The varia- 

 tions of brightness of this star are at times confined within a 

 very few gradations, whereas at others it diminishes from the 

 5th to the 9th magnitude. It has been too little observed to 

 determine when any fixed rule prevails in these deviations. 

 The duration of the period is also subject to considerable 

 fluctuations. 



(12) VirginisR, R. A. 187 43', Decl. + 7 49'. It main- 

 tains its period and its maximum brightness with tolerable 

 regularity ; some deviations, however, do occur, which appear 



