166 ^STOBY OF ASTRONOMY. 



differences of north polar distance made with, the great 

 refractor in 1848 and 1849, found the parallax to be 0".03. 



In the yeUr 1852 Mr. Wichmann published the results 

 of his new series of observations with, the heliometer 

 made in 1851. In these observations he measured the 

 distance between 1830 Groombridge and a small star a 

 preceding by 34' in right ascension, a second star a' fol- 

 lowing it by 34' in right ascension, and a third star a" fol- 

 lowing it by 30' in right ascension. The result of his 

 discussion of the observations was that the parallaxes of 

 the stars a' and a" were of very small amount, but that the 

 parallax of 1830 Groombridge, amounted to 0".71, and 

 that of the star a to 1".17. 



M. Peters has subjected the observations of M. Wich- 

 mann to a critical discussion, and has shown that "Wich- 

 mann's adopted temperature correction is probably too 

 small. He considers the most trustworthy result de- 

 ducible from the observations to be a parallax of 0".148 

 for 1830 Groombridge. 



During the years 1852, '53 and '54, a long series of ob- 

 servations of this star were made by Mr. Johnson with 

 the Oxford heliometer, and these also present an anom- 

 alous result, inasmuch as they assign a greater parallax 

 to one of the stars of comparison than to 1830 Groom- 

 bridge ; and what adds to the perplexity is, that the star 

 which appears to have the greater parallax in this case, 

 is one of those which, in M. "Wichmann's researches 

 appeared to be most distant. Mr. Johnson's results are 

 a parallax of 0".26 for 1830 Groombridge, and of 0".44 



