THE PARALLAX OF FIXED STARS. 163 



greater than has been obtained by either of the preceding 

 observers. 



In 1839, Professor Henderson, of Edinburgh, an- 

 nounced that in discussing his observations of Alpha 

 Centauri made at the Cape of Good Hope, with a mural 

 circle, during the years 1832-3, he had found evidence of 

 a sensible parallax. The double star, a Centauri is one of 

 the brightest stars of the southern hemisphere. The two 

 stars a 1 and a 2 are situated within 19" of space of each 

 other. On comparing the observations of Lacaille with 

 those of the present time, it is found that although the 

 two stars have not sensibly changed their relative posi- 

 tions, each has an annual proper motion of 3.6 seconds 

 of space. It thus appears that they form a binary system, 

 having one of the greatest proper motions that has been 

 observed ; and from this circumstance, as well as the 

 brightness of the stars, it is reasonable to suppose that 

 their parallax may be sensible. Professor Henderson's 

 observations were not made for the purpose of ascertain- 

 ing the parallax, but of accurately determining the mean 

 places of the stars.. On reducing the declinations, he 

 found a sensible parallax, but he delayed communicating 

 the result until it should be seen whether it was confirmed 

 by the observations of right ascension made by Lieutenant 

 Meadows with the transit instrument. These observa- 

 tions also indicated a sensible parallax. A combination 

 of all Professor Henderson's observations gave a parallax 

 of T.16, with a probable error of O'.ll. 



In 1839 and 1840 a series of observations was made by 



