J. C. KAPTEYN, 1851-1922 1 



By A. Van Maanen 



[With 1 plate] 



In Amsterdam, on June 18, Jacobus Cornelius Kapteyn, since 

 1921 retired professor of astronomy and director of the astronomical 

 laboratory at Groningen, died at the age of 71 years. In him astron- 

 omy loses one of its foremost pioneers. 



Kapteyn was born January 19, 1851, at Barneveld, a small village 

 where his father had a well-known boarding school. Of the 15 

 children of this family, several became leaders in the scientific world 

 in Holland. From 1869 to 1875 Kapteyn was a student at the Uni- 

 versity of Utrecht, where his principal teachers were Buys Ballot and 

 Grinwis, so that it is no wonder that his doctoral thesis was in phy- 

 sics : " Onderzoek cler Trillende Platte Vliezen." Just at this time, 

 however, the position of observer at the Leiden Observatory was 

 vacant, and Kapteyn applied for and obtained the position. By this 

 accidental circumstance astronomy secured the privilege of counting 

 Kapteyn as one of its workers and before long as one of its foremost 

 leaders. His ability was soon recognized, and at the age of 27, which 

 for Holland is extremely young, he was appointed full professor in 

 astronomy at the University of Groningen. On entering office, Feb- 

 ruary 20, 1878, his opening address had as subject: " The parallax of 

 the fixed stars." 



The problem of the stellar distances was naturally of first impor- 

 tance to him, whose ideal was to throw some light on the structure 

 of the universe. We do not know when this idea began to ripen in 

 Kapteyn's mind, but it probably dates from the time that he decided 

 to devote his life to astronomy. And no better man could be found 

 to push astronomy ahead along these lines, because Kapteyn had 

 two qualities which were needed for such investigations: He could 

 grasp a great problem and at the same time both could and was 

 willing to devote much time to essential details. These two qualities 

 show up through all his life, and we see him, never losing view of the 

 greatest of astronomical problems, the structure of the universe, and 

 at the same time working with painstaking assiduity to develop and 

 improve the methods of securing the necessary data. Of this part 

 of his work no better example can be given than the succession of new 

 methods that he developed to obtain stellar distances. In 1882 the 



1 Reprinted, by permission, from the Astrophysical Journal, Vol. LVI. No. 3, October, 

 1922. 



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