THE PARALLAX OF FIXED STABS. 167 



for the star of comparison a\ while the parallax of star 

 a was considered to be insensible. These results appear 

 to indicate some imperfection in double-image measures 

 of objects separated by large arcs, which still remains to 

 be explained. 



Mr. Henderson has attempted to determine the par- 

 allax of Sirius from the observations made with the 

 mural circle at the Cape of Good Hope in the years 1832 

 and 1833, as 'also in 1836 and 1837, being in all 231 ob- 

 servations. From these he has deduced a parallax of 

 (T.23. The error of this determination he estimates not 

 to exceed a quarter of a second, from which he concludes 

 that the parallax of Sirius is not greater than half a 

 second of space, and that it is probably much less. 



Numerous attempts have been made to determine the 

 parallax of the pole-star. From a comparison of 603 

 right ascensions of the pole-star observed by M. Struve 

 and Preuss at Dorpat from 1822 to 1838, M. Peters has 

 deduced a parallax of OM7, with a probable error 

 of 0".03. From a comparison of the declinations of the 

 pole-star observed at Dorpat from 1822 to 1838, M. 

 Peters has deduced a parallax of 0".15; and by com- 

 paring the right ascensions observed at Dorpat from 1818 

 to 1821, he has deduced the parallax of 0*.07. M. De 

 Lindenau, from a comparison of 890 right ascensions of 

 the pole-star, observed by different astronomers, deduced 

 a parallax of OM4, with a probable error of 0".06. From 

 289 observations of the pole-star made at Pulkova in 1842 

 and 1843 with the grand vertical circle of Ertel, M. Peters 



