158 A CENTURY'S PROGRESS IN ASTRONOMY. 



The method of absolute parallax, on the other 

 hand, the star's displacement in right ascension 

 and decimation, has been seldom used, owing 

 to the laborious reduction which has to be gone 

 through before the result can be reached. In 

 1885, however, a series of observations were 

 undertaken at Leyden by Jacobus Cornelius 

 Kapteyn (born 1851), who determined by the 

 absolute method the parallaxes of fifteen north- 

 ern stars. 



The first application of photography to the 

 problem was due to the zeal and energy of 

 Charles Pritchard (1808-1893), Professor of 

 Astronomy at Oxford, who determined by this 

 method the parallax of 61 Cygni, which he 

 announced in 1886 to be 0*438", in agreement 

 with Ball's determination. He also determined 

 the average parallax of second-magnitude stars, 

 which came out as 0'056". Since the time of 

 Pritchard's observations various other more or 

 less satisfactory determinations of parallax have 

 been made. Few of the parallax determinations 

 are probably very accurate, and none exact ; but 

 an idea of the difficulty of the measurement may 

 be gathered from the remark of an American 

 writer, Mr G. P. Serviss, that the displacement 

 " is about equal to the apparent distance between 

 the heads of two pins, placed an inch apart, and 



