OLBERS, HEINRICH WILHELM MATTHIAS

(b. Arbergen, near Bremen, Germany, 11 October 1758; d. Bremen, 2 March 1840)

medicine, astronomy.

Olbers was the eighth of the sixteen children of Johann Jürgen Olbers, a Protestant minister. He became interested in astronomy when he was about fourteen, but the Gymnasium in Bremen which he attended was a typical humanistic institution of that time where almost no mathematics or science was taught. In order to understand astronomy Olbers taught himself mathematics and tried to compute the solar eclipse of 1774. In 1777 he began the study of medicine in Göttingen under Blumenbach and Ernst Baldinger, and also attended lectures in physics and mathematics by G. C. Lichtenberg and, especially, A. G. Kästner, who was in charge of the small observatory at Göttingen. But mainly he studied astronomy on his own. His lifelong concern with comets dates from January 1779, when he used his observations of Bode’s comet to calculate its orbit according to Euclid’s method. In 1780 he independently discovered a comet that was simultaneously observed by Montaigne. Meanwhile, Olbers continued his medical studies, concentrating on a problem that involved the application of mathematics to physiology. His dissertation, De oculi mutittionibus (Göttingen, 1780), explains how the eye adapts to a change in focus by changing the shape of the eyeball; only much later was it discovered that only the lens changes shape. Later, as a practicing physician he specialized in ophthalmology, a field hardly recognized at that time.

In 1781, after receiving his medical degree at Göttingen, Olbers went on a study trip to Vienna, where he visited hospitals during the day, enjoyed the aristocratic social life of the city in the evenings and spent the nights at the Vienna observatory. Throughout his life he profited from needing only four hours of sleep, so that after a long and busy day of practicing medicine he could “relax” by observing the sky. In Vienna he was thus able to follow the course of the recently discovered planet Uranus.

At the end of 1781 Olbers settled in Bremen and soon acquired an extensive medical practice. It was mainly through his efforts that inoculation was introduced in the city, and he was highly praised for his work during several cholera epidemics. When the “magnetic cures” of Mesmer started a great controversy, Olbers published an article admitting the reality of some of them but also expressed the opinion that future understanding of physiology would explain them without the assumption of a special power.

In 1785 Olbers married Dorothea Köhne, who died a year later at the birth of their daughter. In 1789 he married Anna Adelheid Lurssen, by whom he had one son. After the death of his daughter in 1818 and of his second wife in 1820, he retired from active medical practice to devote the rest of his life to astronomy.

Olbers installed an observatory on the second floor of his house, using its two large bay windows for his telescopes. At various times he possessed two achromatic Dollond refractors, a Schröter reflector, a heliometer and refractor from Fraunhofer’s workshop. and three comet seekers, made by Hofmann, Weickhardt, and Fraunhofer. He had no transit instrument or fixed instrument of any kind. His library became one of the best private astronomical collections in Europe. For over fifty years he carefully gathered astronomical literature and assembled a collection in the field of cometography that was practically complete. After Olbers” death, F. G. W. Struve bought this library for the new Pulkovo Observatory, near St. Petersburg. Struve’s new catalog of the collection listed 4,361 items, consisting of 39 sky charts, 1,607 monographs, and 2,715 articles.

Busy with his new medical practice when he first moved to Bremen, Olbers had less time for astronomy; but in 1786 he met J. H. Schröter, whose private observatory in nearby Lilienthal was one of the best-equipped on the Continent, and they worked closely together for many years. In 1796 Olbers discovered a comet and calculated its parabolic orbit with a new method, simpler than that used by Laplace. In a letter to F. X. von Zach, director of the newly founded observatory on the Seeberg, near Gotha, Olbers asked whether his treatise on this method should be printed, and if so, how this could best be done. After reading the treatise and using it with excellent results to compute the orbit of the comet of 1779, which had presented great difficulties to many astronomers, von Zach decided to see it through the press himself. It appeared at Weimar in 1797 under the title Über die leichteste und bequemste Methode, die Balm eines Kometen am einigen Beo-bachtungen zu berechnen. This work immediately established Olbers among the foremost astronomers of his time, and his method was used throughout the nineteenth century.

Despite the work of Newton and Lambert, the computation of cometary orbits had until then been. a very laborious process. Laplace had given formulas for the computation of a parabola through successive approximations, but the procedure was cumbersome and unsatisfactory. It had been assumed that when three observations of a comet had been obtained within a short period of time, the radius vector of the middle observation would divide the chord of the orbit of the comet from the first to the last observation in relation to the traversed time. The finding that this assumption could be applied with equal advantage to the three positions of the earth in its orbit was Olbers’ contribution. This basic idea led to a rapidly converging process of calculation, and Olbers worked out simple and easily calculated formulas.

The space between the planets Mars and Jupiter, shown mathematically by Bode’s law. had long intrigued astronomers. The first asteroid was discovered by G. Piazzi at the Palermo observatory on 1 January 1801. He noticed a starlike object that moved during the succeeding days. He communicated this news to other astronomers; and although it was soon realized that this must be a new planet, named Ceres by Piazzi, it disappeared before more observations could be made. At that time it was still impossible to compute an orbit from such a small arc without assuming the eccentricity. Then the twenty-three-year-old Gauss was able to determine the orbit by a new method; and it was Olbers who, on 1 January 1802, found the new planet very near where Gauss had calculated it would be. This episode was the beginning of their lifelong friendship; and when Gauss visited Olbers in 1803, each had his portrait painted to give to the other. The two portraits now hang in the Göttingen observatory. While following Ceres, Olbers discovered a second asteroid, Pallas, on 28 March 1802; a third, Juno, was discovered by Harding at Lilienthal in 1804. The orbits of these small planets suggested to Olbers that they had a common point of origin and might have originated from one large planet. Accordingly, for years he searched the sky where the orbits of Ceres, Pallas, and Juno approached each other; the result was the discovery of Vesta on 29 March 1807.

The search for comets remained Olbers’ main interest, and his industry was rewarded with the discovery of four. Of particular interest is the comet that he discovered on 6 March 1815, which has an orbit of seventy-two years, similar to Halley’s. Olbers also calculated the orbits of eighteen other comets. Noticing that comets consist of a starlike nucleus and a parabolic cloud of matter, he supposed that this matter was expelled by the nucleus and repelled by the sun. In “Über die Durchsichtigkeit des Weltraums,” published in 1823 in Berliner astronomisches Jahrbuch für das Jahr 1826, Olbers discussed the paradox that now bears his name: If we accept an infinite, uniform universe, the whole sky would be covered by stars shining as brightly as our sun. Olbers explained the paradox of the dark night sky by assuming that space is not absolutely transparent and that some interspace matter absorbs a very minute percentage of starlight. This effect is sufficient to dim the light of the stars, so that they are seen as points against the dark sky. The idea was not absolutely new; Halley had written about it and a young Swiss astronomer, Jean Philippe Loys de Chéseaux, had published an essay in 1744 using a very similar argument.

Olbers was also interested in the influence of the moon on weather, the origin of meteorite showers, and the history of astronomy. He was a member of Museum, the scientific society in Bremen, and through the years gave over eighty lectures there (of which only one was on a medical subject).

Although Olbers usually declined official posts, he felt it his duty to participate in the government during the time that Bremen was part of the French empire (1811–1813). This commitment forced him to spend time in Paris, where he met some of the French astronomers.

Olbers was held in great esteem by his contemporaries. He conducted an extensive correspondence with Gauss, Bessel, Encke, Schröter, and other astronomers. He also encouraged many young astronomers with good advice and made great efforts to obtain positions for them at various observatories. One of them, Friedrich Wilhelm Bessel, a twenty-year-old apprentice in a merchant’s office, had approached Olbers in 1804 with his calculation of the orbit of Halley’s comet. Olbers was so impressed with his work that, after suggesting some additions, he recommended it for publication and sought to obtain the directorship of the new observatory at Königsberg for Bessel.

A very modest man, Olbers later claimed that his greatest contribution to astronomy had been to lead Bessel to become a professional astronomer. Bessel’s eulogy, written in 1845, ended: “He was to me the most noble friend. With wise and fatherly counsel he guided my youth; 171 letters which I possess from him are written proof of my right to extend my devotion beyond the limits of science”

BIBLIOGRAPHY

I. Original Works. Olbers’ article on Mesmer’s cures is “Erklärung über die in Bremen durch den sogenanntcn Magnetismus vorgenommenen Kuren,” in Deutsches Muséum (Oct. 1787), 296–312. A complete listing of his almost 200 articles is in vol. I of C. Schilling, Wilhelm Olbers, sein Leben und seine Werke, 2 vols. in 3 pts. and supp. (Berlin, 1894–1909); this work also contains the complete correspondence with Gauss. Olbers’ correspondence with Bessel was published by A. Erman, Briefwechset zwischen W. Olbers and F, W. Bessel, 2 vols. (Leipzig, 1852). The Staatsbibliothek in Bremen has a collection of Olbers’ papers.

II. Secondary Literature. Von Bremer Astronomen und Stemfreunden,W. Stein, ed. (Bremen, 1958), contains six papers on various aspects of Olbers’ career and a partial listing of his works. Bessel’s obituary is in Astronomisehe Nachrkhtetu22 (1845), cols. 265–270. Another, unsigned obituary is in Proceedings of the Royal Society, 4 (1837–1843), 267–269. Struve reported on the purchase of Olbers’ library for the observatory at Pulkovo in Astronomisehe Nachrichten, 19 (1842), 307–312. The paradox of the dark night sky is extensively treated by Stanley L. Jaki in The Paradox of Others Paradox (New York, 1969). See also Otto Struve, “Some Thoughts on Olbers’ Paradox’ in Sky and Telescope, 25 (1963), 140–142; and Stanley L. Jaki, “New Light on Olbers’ Dependence on Chéseaux,” in Journal for the History of Astronomy1 (1970), 53–55. F. X. von Zach describes Olbers’ observatory and instruments in “Auszug aus einem astronomischen Tagebuche, geführt auf einer Rcise nach Celle, Bremen und Lilienthal in Sept. 1800,“; in Monatliche Correspondez…,3 (1801), 113–145. There is a biographical notice in Allgemeine deutsche Biographic XXIV, 236–238.

Lettie S. Multhauf