DOUBLE STARS. 



ance of that observer with the region of the firmament in which 

 he saw it, he was quite certain that, previous to the 5th April, 

 no star brighter than those of the ninth magnitude had been 

 there, nor is there any star in the catalogues at all corresponding 

 to that which he saw there on the 28th. This star continued to 

 be seen until the advance of the season and its low altitude 

 rendered it impossible to be observed. It, however, constantly 

 diminished in lustre until it disappeared, and has not since been 

 seen. 



47. To the class of temporary stars may be referred the cases 

 of numerous stars which have disappeared from the firmament. 

 On a careful examination of the heavens, and a comparison of the 

 objects observed with former catalogues, and of catalogues ancient 

 and modern with each other, many stars formerly known are now 

 ascertained to be missing ; and although, as Sir John Herschel 

 observes, there is no doubt that in many instances these apparent 

 losses have proceeded from mistaken entries, yet it is equally 

 certain that in numerous cases there can have been no mistake 

 in the observation or the entry, and that the star has really existed 

 at a former epoch, and certainly has since disappeared. 



When we consider the vast length of many of the periods of 

 astronomical phenomena, it is far from being improbable that 

 these phenomena, which seem to be occasional^ accidental, and 

 springing from the operation of no regular physical causes, such 

 as those indicated by the class of variable stars first considered, 

 may after all be periodic stars of the same kind, whose appear- 

 ances and disappearances are brought about by similar causes. 

 All that can be certainly known respecting them is, that they have 

 appeared or disappeared once in that brief period of time within 

 which astronomical observations have been made and recorded. 

 If they be periodic stars, the length of whose period exceeds that 

 interval, their changes could only have been once exhibited to us, 

 and after ages have rolled away, and time has converted the 

 future into the past, astronomers may witness the next occur- 

 rence of their phases, and discover that to be regular, harmo- 

 nious, and periodic, which appears to us accidental, occasional, and 

 anomalous. 



DOUBLE STARS. 



When the stars are examined individually by telescopes of a 

 certain power, it is found that many which to the naked eye 

 appear to be single stars, are in reality two stars placed so 

 close together that they appear as one. These are called double 

 stars. 



48. A very limited number of these objects had been discovered 



203 



