Page:Popular Science Monthly Volume 39.djvu/569

Rh, of which the northern lights only is mentioned, in which Argelander had a great interest. He had made many observations 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 important features in June, 1843, although a few gaps remained to be filled in March and April, 1844. Argelander was so busy in trying 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 attention 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 Bessel'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 Durchmusterung 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 unfolded the plan of the star charts to the Berlin Academy, contemplated 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 observations, 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 Bessel'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 observation and reduction employed in the Bonn Durchmusterung, which resulted in the great sky-atlas and catalogue of 324,198 stars