156 A CENTURY'S PROGRESS IN ASTRONOMY. 



and Otto Struve at Pulkowa were among the 

 most famous parallax-hunters in the middle of the 

 century. One of the most successful searchers 

 after parallax was the German astronomer Fried- 

 rich Briinnow (1821-1891), who was employed 

 from 1865 to 1874 as Astronomer-Royal of Ire- 

 land. He determined the parallax of Vega as 

 0*13", and this was confirmed in 1886 by Hall 

 at Washington : while he measured the parallax 

 of the star Groombridge 1830, which turned out 

 to be 0'09". He resigned his post in 1874, and 

 his successor at Dublin Observatory proved to 

 be his successor also in this branch of astronomy. 

 Robert Stawell Ball, born in Dublin in 1840, 

 was astronomer to Lord Rosse in 1865 and 1866, 

 and became in 1874 Astronomer-Royal of Ire- 

 land in succession to Briinnow, a position which 

 he filled until his appointment in 1892 as Pro- 

 fessor of Astronomy at Cambridge, and director 

 of the observatory there. During his term of 

 office in Dublin he undertook, in 1881, a 

 " sweeping search " for large parallaxes, thereby 

 disproving certain ideas as to the proximity to 

 the Earth of red and temporary stars; while 

 he also determined the parallax of the star 

 1618 Groombridge. 



But the greatest extension of our knowledge 

 of stellar distances, in recent years, is due to a 



