NEW AND VARIABLE STARS. 171 



as of the fourth magnitude ; yet in Lacaille's in 1751, and 

 in subsequent catalogues, it is recorded as of the second 

 magnitude. In the interval from 1811 to 1815, it was 

 again of the fourth ; and again from 1822 to 1826 of the 

 second magnitude. In 1827, it increased to the first 

 magnitude ; it thence receded to the second, and so con- 

 tinued until the end of 1837. In the beginning of 1838, 

 it suddenly increased in luster so as to surpass all the 

 stars of the first magnitude except Sirius, Canopus, and 

 Alpha Centauri, which last star it nearly equaled. 

 Thence it again diminished, and in 1842, it was pro- 

 nounced by Maclear as inferior to Alpha Crucis, but the 

 next year it again revived, and became nearly equal to 

 Sirius. 



These facts afford abundant materials for speculation. 

 The changes of brightness of TJ Argus are spread over 

 centuries, and apparently without any regular period. 

 What can be the cause of these changes ? To this ques- 

 tion we are unable to assign any satisfactory answer, 

 and must wait patiently until a greater accumula- 

 tion of facts shall afford us a more certain basis for a 

 theory. 



Several instances are on record of temporary stars, 

 which have suddenly become visible, and after remaining 

 a while, apparently immovable, have died away and left 

 no trace behind. Such a star is said to have appeared 

 about the year 125 B. C. Such stars are also recorded 

 in the years A. D. 389, 945, 1264, 1572, 1604, and 1670. 

 A similar -phenomenon has recently taken place. On the 



