VARIABLE STABS. 233 



EXPLANATORY REMARKS. 



The in the column of the minima indicates that the 

 star is then fainter than the 10th magnitude. For the 

 purpose of clearly and conveniently designating the smaller 

 variable stars, which for the most part have neither names 

 nor other designations, I have allowed myself to append to 

 them capitals, since the letters of the Greek and the smaller 

 Latin alphabet have, for the most part, been already employed 

 by Bayer. 



Besides the stars adduced in the preceding table, there 

 are almost as many more which are supposed to be variable, 

 since their magnitudes are set down differently by different 

 observers. But as these estimates were merely occasional, 

 and have not been conducted with much precision, and as 

 different astronomers have different principles in estimating 

 magnitudes, it seems the safer course not to notice any such 

 cases, until the same observer shall have found a decided 

 variation in them at different times. With all those adduced 

 in the table this is the case ; and the fact of their periodical 

 change of light is quite established, even where the period 

 itself has not been ascertained. The periods given in the 

 table are founded, for the most part, on my own examination 

 of all the earlier observations that have been published, and 

 on my own observations within the last ten years, which have 

 not as yet been published. Exceptions will be mentioned in 

 the following notices of the several stars. 



In these notices the positions are' those for 1850, and are 

 expressed in right ascension and declination. The frequently 

 repeated term gradation indicates a difference of brightness, 

 which may be distinctly recognized even by the naked eye, or 

 in the case of those stars which are invisible to the unaided 

 sight, by a Frauenhofer's comet-seeker of twenty-five and 

 a-half inches focal length. For the brighter stars above the 

 6th magnitude, a gradation indicates about the tenth part 

 of the difference by which the successive orders of mag- 

 nitude differ from one another; for the smaller stars the 

 usual classifications of magnitude are considerably closer. 



(1) o Ceti, R. A. 32 57', Decl. 3 40'; also called Mira, 

 on account of the wonderful change of light which was first 

 observed in this star. As early as the latter half of the 

 seventeenth century", the periodicity of this star was recog- 

 nized, and Bouillaud fixed the duration of its period at 333 



