land was also his wedding tour; and he went "by way of Dorpat, where he renewed his friendship with Struve, and St. Petersburg. The observatory at Åbo, newly built, was not yet fully furnished, and the nature of the observations was considerably determined by the consideration of the instruments that were available. The earlier ones were upon comets, and those made with the meridian circle; and Argelander computed the orbit of the comet of 1718 from Kirch's observations.
Attention was next given to the proper motions of the stars, the study of which, although touched upon by Bradley and resumed by Piazzi, was still in its beginning. At this time the Königsberg Observatory was extending the knowledge of the stars in mass; Dorpat, that of double stars; and Greenwich, that of stars visible to the naked eye; and Argelander devoted his observatory to the stars the yearly motion of which was given by Bradley and Piazzi as 0·2" or more, as well as of those of which were suspected of having motions. These stars were to be observed at least four times a year, in every position of the circle.
The observations made at Åbo were published down to 1828, in three volumes, while the rest were still awaiting publication at the time of Argelander's death. The steps taken to insure the highest accuracy are fully set forth in the introduction to the second volume. The catalogue at once took a first place among the records which gave the fundamental determinations of the star places for 1830. It is also a model for convenience.
The buildings, collections, and library of the university having been destroyed by the great fire which visited Åbo in September, 1827, although the observatory was saved, it was determined to remove the whole concern to Helsingfors. Argelander was appointed a Professor in Ordinary of Astronomy in the new university, but did not remove from Åbo till 1831. Then, having visited his old home after eight years of absence and renewed his association with Bessel, he settled in Helsingfors in August, 1832, while the buildings were still in a backward condition, so that he was not able to make an observation for nearly a year, and all was not complete till September, 1835. To the Helsingfors period belong observations of the brighter circumpolar stars, of the bending of the meridian circle, and the printing of the Åbo catalogue; and the celebrated treatise on the proper motion of the solar system. Supported by the results obtained at Åbo, he found that the regularity of the stellar motions, which is explained by a movement of the sun toward the constellation Hercules, first tentatively announced by Herschel, was borne out by the observations.
In August, 1836, Argelander was invited to remove to the still young University of Bonn, where the Prussian Government had
