SKETCH OF FRIED RICH W. A. ARGELANDER. 553 



nomena, of which the northern lights only is mentioned, in which 

 Argelander had a great interest. He had made many observa- 

 tions on it in Finland, which he afterward published. 



These accounts of special works of Argelander have caused 

 us to anticipate much of the course of events. We return to the 

 beginning of his life in Bonn. While still in the temporary 

 building, having with great care obviated some of the defects of 

 the structure, he proceeded to continue Bessel's zones to the north, 

 from 45 to 80 declination. Thus originated the northern zones, 

 containing 26,424 observations of nearly 22,000 stars. They were 

 begun May 27, 1841, and were concluded as to their most import- 

 ant features in June, 1843, although a few gaps remained to be 

 filled in March and April, 1844. Argelander was so busy in try- 

 ing to bring them to a close that, although much interested in 

 such bodies, he did not find time to observe the great comet of 

 1843 in the earlier days of its appearance. 



After the completion of the new observatory in 1845, while 

 still keeping on with the meridian observations, Argelander's at- 

 tention was directed by the discoveries of new planets and comets, 

 that were numerous in the years following, to lesser fields. The 

 lack of exact definitions of star places south of the limits of Bes- 

 sel's zones led him to the examination of the southern zones, of 

 which he took, between May, 1849, and May, 1852, in 200 zones, 

 23,250 observations of more than 17,000 stars. The accuracy of 

 these observations is somewhat unequal, but is yet sufficient for 

 the most southern zones, and is for the brighter stars hardly less 

 than that of Bessel's observations, The connection of the two 

 great labors of the Durchmusteruny was steadily kept in view. 

 But, before the southern zones were done, Argelander had formed 

 the plan of a still larger work. Bessel had already, when he un- 

 folded the plan of the star charts to the Berlin Academy, contem- 

 plated the complete place-determination of all the stars to the 

 ninth magnitude ; but this had not been accomplished, even after 

 the lapse of a quarter of a century. Argelander had tentatively 

 finished one sheet at great expense, and begun another which he then 

 left to others. When, on the completion of the southern observa- 

 tions, the materials for the charts had come into his hands again 

 and more force was at the disposition of the observatory for other 

 work, Argelander thought the time had come for executing Bes- 

 sel's old plan. Two men were engaged at once the astronomer at 

 the telescope and a secretary in an adjoining lighted room to note 

 down the time ; and, to economize the time for a work of such 

 magnitude, two pairs of observers alternated with one another. 

 Argelander himself published a description of the methods of ob- 

 servation and reduction employed in the Bonn Durchmusterung , 

 which resulted in the great sky-atlas and catalogue of 324,198 stars 



