Horrebow, Peder Nielsen

(b Løgstør, Denmark, 14 May 1679; d. Copenhagen, Denmark, 15 April 1764)

astronomy.

Born into the family of a poor fisherman, Horrebow had to work his way through grammar school and later through Copenhagen University by doing mechanical work. He was a personal assistant to Ole Römer for four years. In 1714 he was made professor at the university and director of the observatory; he held this position for fifty years, although two of his sons had to take care of his professional duties during his last years. He was a member of the academies of Copenhagen, Berlin, and Paris.

Horrebow’s scientific life was shaped by two major influences. The first was his daily association during his youth with Römer, of whom Horrebow later spoke with the greatest devotion. Second, in the great fire in Copenhagen in 1728 nearly all of Römer’s papers and unpublished observations were destroyed together with Horrebow’s own observations; and from that time on it remained a matter of personal honor for Horrebow to describe fully Röer’s scientific achievements in order to preserve them for posterity.

Horrebow’s book on Römer, the classic Basis astronomiae (1734–1735), contained Römer’s observations, which Horrebow made with his own meridian circle during three days and nights. These observations were soon being used in early determinations of proper motions.

A main problem of the times was the measurement of the annual parallax of the fixed stars. Römer had introduced a new method, well adapted for his own instruments, in which the observation of the time of transit over the meridian was central. After Römer’s death Horrebow analyzed the parallax traceable in the observations. He published his results in 1727 in a book with the exultant title Copernicus triumphans, which was received with great interest in the astronomical world. But in 1848 C. A. F. Peters disproved Horrebow’s results through a systematic run of the clocks.

In 1732, in his book Atrium astronomiae, Horrebow advanced a technique for determining geographical latitude, now known as the Horrebow-Talcott method since it was rediscovered a century later by the American soldier and engineer Andrew Talcott. From his collection of notes entitled Adversaria, it appeared possible that Römer himself had known this method; but in the light of Horrebow’s known commitment to point out his teacher’s contributions and of his statement that he himself found it, the naming of it for him must be regarded as justified.

Throughout his lifetime Horrebow was a fertile author. He wrote several textbooks on astronomy, mathematics, and navigation which had a considerable influence at the university and at Danish schools.

BIBLIOGRAPHY

I. Original Works. Several of Horrebow’s works have been collected in Operum mathematico-physicorum, 3 vols. (Copenhagen, 1740–1741); his Copernicus triumphans (reprinted in Operum, III) was translated into Dutch (Zutphen, 1741). See also his Danske Skatkamer, bestaaendeudi Grunden til Geometrien og Nauigationen (Copenhagen, 1743–1746) and Elementa philosophiae naturalis (Copenhagen, 1748).

II. Secondary Literature. Articles on Horrebow are Dansk Biografisk Lekiskon, X (1936), 611–613; and J. Bernoulli, Recueil pour les astronomes, supplement (Berlin, 1779), 62–71. See also C. A. F. Peters, “Recherches sur la parallaxe des étoiles fixes,” in Mémoires de L’Académie impériale des sciences de St.-Pétersbourg, Sec. mathphys., 5 (1848), 15–18; P. Kempf, “Ist man berechtigt, die Methode der Breitenbestimmung aus reziproken Höhen auf Römer zurückzufüren?” in Astronomische Nachrichten, 136 (1894), 11–14; and John E. McGrath, “A Question of Priority in Originating a Very Important Astronomical Method—Römer or Horrebow?” in Journal of the Royal Astronomical Society of Canada, 8 (1914), 36–40.

Axel V. Nielsen