Popular Science Monthly/Volume 39/August 1891/Sketch of Friedrich W. A. Argelander



ARGELANDER, says Prof. E. Schoenfeld, was pre-eminently an astronomical observer. In his youth he could handle every instrument as he could his pen. With his great keenness of vision, this occupation was attractive to him; but he realized that it was a means to an end. He found his life-work in collecting materials for a theory of the universe. Most of his work in Bonn was devoted to acquiring the completeness attainable under the limited capacity of the instruments in use in the knowledge of the fixed stars. To him we owe the demonstration of the proper motion of the solar system through space, and one of the fullest and most accurate of the older charts and catalogues a work which remains a standard for reference. The materials for our sketch are derived wholly from the biography published shortly after his death by Prof. Schoenfeld, his successor at Bonn, in the Vierteljahrsschrift der astronomischen Gesellschaft.

Friedrich Wllhelm August Argelander was born On the 22d of March, 1799, at Memel, in East Prussia, and died at Bonn, February 17, 1875. He was the son of the merchant Johann Gottfried Argelander, of descent on the father's side from Finland, while his mother was German. The relations of the family with the outer world favored the most careful training of the future astronomer. The political conditions existing during his childhood brought him early into closer relations with the great world than could have been expected to arise in the ordinary course of events in the little village so remote from the capital. The Prussian royal family had left Berlin after the unfortunate issue of the campaign of 1806, and ultimately retired to Memel. The crown prince, afterward King Friedrich Wilhelm IV, and Prince Friedrich lived in the house of Argelander's parents; and, notwithstanding the difference of three years and a half in their ages, a warm and lasting friendship was formed between the former and Argelander. Hardly less cordial was the relation of Prince Wilhelm, the late Emperor of Germany. But the times were in all other respects times of trial; and because of this the inner life was all the more richly developed. Argelander afterward attended the Gymnasium of Elbring, and, in 1813, the Collegium Fridericianum at Königsberg. When, in 1817, he entered the university he enrolled himself as a student in financial science, and devoted himself earnestly to it; but he soon found himself more attracted to Bessel's astronomical lectures than to all the others.

Having made sufficient advance to undertake work of that kind, he asked Bessel to intrust him with some of the calculations for the observatory. Bessel, who had then completed his Fundamenti Astronomiæ, gave him some calculations of stars not observed since Bradley that he had identified, and the problem of determining the latitude of the observatory from observation of the pole star not yet worked out. The publication of the results of these labors in the Königsberg observations introduced the author to the scientific world as Bessel's most capable pupil. Other similar calculations followed, and Argelander showed a growing devotion to practical astronomy.

The observation of an occultation of the Pleiades in August, 1820, was regarded by Argelander as his first astronomical observation; and he held a vivid recollection of its incidents in his later years. In October following he was appointed, on Bessel's nomination, assistant at the observatory. Bessel had conceived his plan for a Durchmusterung, or sounding of the sky, and had begun upon it, and wanted another astronomer. He employed Argelander to assist him in reading and writing down the micrometric indications on the circle. While waiting for this work to begin, Argelander made observations on setting stars, which were used by Bessel in completing his refraction tables to zenith distances 85° and 891/2°, and in observing the comet of 1821. His first independently published paper, written in 1821, as a thesis for the degree of Ph. D., was on Flamstead's Astronomical Observations, and largely concerned the errors of his instruments. A memoir on the comet of 1811 was published shortly afterward. It recorded fuller observations, and covering more time, than had been made before of any comet. Relying upon Bessel's methods for the comets of 1807 and 1815, and realizing that the value of labors of the kind lay in treating the observations exhaustively, he went back to the very beginning of them. Some unexpected difficulties met in the calculations, involving among other things apparent disagreements with the law of gravitation, led him to suppose that some abnormal force worked upon the comet—a hypothesis that was not without influence on Bessel's views concerning the repulsive force of comets' tails. Although Bessel further developed these views in his work on Halley's comet, and in the controversy with Encke, respecting the resisting medium, Argelander was afterward inclined to modify his own opinions, and to hold the question open whether the movements of comets pointed to the operation of foreign forces upon them. On the faith of this paper Argelander was given a license to teach in the university.

The place of Observer at the Observatory of Abo, Finland, having been made vacant by the death of Walbeck, Bessel was applied to to name a successor. He recommended Argelander, who was appointed in April, 1823. Argelander's journey to Finland 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 determined to erect a great astronomical institution. He found most of the labor of fitting up the observatory yet to be done. He was given, as temporary quarters, with poor provisions for his work, a bastion on the Rhine called the Old Zoll.

With irrepressible industry he composed his beautiful work, the New Uranometry, or charts of the stars visible to the naked eye in central Europe, with their true magnitudes taken immediately from the sky. Taking up the field, hitherto but little worked, of the variable stars, he adopted the methods of Herschel, improving the notation. He expressed all the differences in light by numbers, and thereby opened the possibility of investigating phenomena which no one before him had subjected to calculation. Beginning in December, 1838, with observations of Mira Ceti, he included Algol in February, 1840, β Lyræ and other stars in the summer of the same year, and, with these, telescopic stars. At the same time he tried to excite interest in the subject in other quarters, at first with limited, afterward with increasing success; and in a short time this branch of our knowledge of the fixed stars assumed a new form. The discovery in 1843 of the decrease in Algol's period led to more thorough researches on the changes of the periods and their laws. Closer examinations of the older observations were brought in, and much that had been almost lost was looked up and collected. The observations were continued for many years, and it was not till 1859 that Argelander, without giving up his interest in the work, ceased to prosecute it actively, when his eyes were becoming weak, and when the general participation of others in it had satisfied him that it would be carried on.

The New Uranometry had originated, not only in the desire to present an enumeration of the stars, to clear the charts of errors of position and designation, and to furnish observers with the naked eye Avith a good atlas for orientation, but also out of the conviction of the importance of leaving to posterity a good representation of the relative magnitudes of the brighter fixed stars, in order to make the real secular variations in brightness distinguishable from fancied ones. The dissertation, De fide UranometricB Bayeri, is a contribution in this direction, and has the great merit of setting out in the right light the true principles from which Bayer had allowed himself to be led in the construction of his charts. Argelander's methods of observation in this field are summarized in an essay in Schumacher's Jahrbuch for 1844, from which many who have interested themselves in this line have drawn their instructions. The same work contains the first general summary of our knowledge of the subject from Argelander's hand, an important revision of which is found in Humboldt's Cosmos. This treatise also bespeaks many other phenomena, 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 between the north pole and two degrees of south declination. Leaving the execution of these observations to his assistants, Argelander started with Struve, in June, 1852, by way of Göttingen and Berlin, to Sweden and Finland, and thence to Pultova, where he spent four weeks, to return at the end of September with the best impressions and in full vigor. The winter and spring of 1854 were so favorable to observations, while the reduction-tables were not far behind them, that Argelander could rejoice in the thought that the atlas would contain from fifty to a hundred thousand more stars than he had originally contemplated. Ever careful to preserve the unity of the whole, he arranged most of the materials himself, and was not willing to let a zone pass without personally working upon it. Double stars and stars with greater proper motions were noted; Winnecke's and Kruger's determinations of parallax were connected with these, and the restoration of lost stars from the older observations afforded ever-new interest. The revisions went on till the summer of 1861; but in some of the regions they no longer required all of Argelander's time, and he was able to pursue other objects. He identified all the stars of the eighth magnitude and brighter, which were not found in the earlier catalogues, with the accessible variable stars, the stars for comparison with the Mannheim observations of nebulæ and for former appearances of periodical comets, and especially many stars with presumed or determined proper motions. Next, while still occupied with the collation of his material, Argelander turned his eye to a work he had long contemplated, of more exact meridian observations of all the stars to the ninth magnitude, of which the Durchmusterung had made known the general positions. The labor, too much for a single establishment, was to be divided among different observatories. So, in the summer of 1865, he made a proposition for the simultaneous observation of selected stars at different points, by which he hoped to obtain material for the investigation of star catalogues in general, and to secure the needed number of fixed points for the greater work. The plan for this work was first presented, in 1867, to the officers of the University at Bonn, and afterward at the general meeting of the Astronomische Gesellschaft, where the author also gave his views respecting the most convenient way of carrying it out. With some slight modifications they form the basis of the programme decided upon by the society at Vienna in 1869.

Argelander undertook a small part of the preliminary work for the execution of this scheme, but found that, at the age of seventy years, he was no longer competent to make the necessary observations, and he gave them over to his assistants, carrying on himself only the minor series. The main part of the treatise on the subject was printed only a short time before his death.

Argelander was less versed in the deeper theories of astronomy than in practical work. Hence those of his lectures that had a practical bearing were most interesting, and so searching was he that, whenever he found hearers, he aroused their earnest interest. He was fond of personal intercourse with his students, and would often walk with them, conversing on various subjects, questions of the day, etc. He would go into detailed and most entertaining discussions, for which his lectures afforded neither time nor a suitable public, and he could then consider the value of conjectural hypotheses to which he was no friend. The transparency of his character, the goodness of his heart, and his open, manly bearing will never be forgotten by his friends.

His active life was not wanting in distinctions. He wore orders conferred by Russia, Prussia, Sweden, and Baden. Numerous learned societies and academies made him an active, corresponding, or honorary member; those of St. Petersburg in 1826, of Berlin in 1836, of London (not more distinctly named) in 1846, of Stockholm in the same year, of Paris and Vienna in 1851, of Berlin in 1855, of Breslau in 1856, the Royal Astronomical Society of London in 1832, the Societas Fennica at Helsingfors in 1845, and the National Academy of the United States in 1864. He received the Demidoff prize of the St. Petersburg Academy while residing at Helsingfors, and the golden medal of the Royal Astronomical Society in 1863. The jubilee of his receiving the doctor's degree was made the occasion of a grand celebration in 1872. He was almost from its foundation a member of the official board of the Astronomische Gesellschaft, and presided at the meetings in Bonn and Leipsic.

Many positions were offered to him, but he preferred to remain at Bonn, while he always preserved an affectionate recollection of Finland. He devoted himself faithfully to the interests of the observatory, but was not fond of participating in affairs of administration, and was disinclined to public life. He was a welcome guest at the social gatherings of scientific societies.

Accepting, provisionally, D'Omalius d'Halley's estimate of the population of

the earth, 1,195,450,000, M. H. R. Verneau calculates that forty-two per cent of the number are of the white race, forty-four per cent of the yellow race, eleven per cent are negroes, two per cent of the mixed Oceanic races, and one per cent Indians. By local distribution, the whites occupy twenty-two per cent of the habitable surface of the globe, the yellow races twenty-eight per cent, the negroes eighteen per cent, the Oceanians three per cent, and the American Indians twenty per cent. Hence, as distributed, there are found, on equal areas inhabited by them, one Indian, nineteen negroes, twenty-one Oceanians, fifty of the yellow races, and sixty-one whites. In point of religion, 400,000,000 of the earth's inhabitants are

Christian adherents of various sects.