Arrest, Heinrich Louis D’

(b. Berlin, Germany, 13 August 1822; d. Copenhagen, Denmark, 14 June 1875)

astronomy.

A diligent investigator of comets, asteroids, and nebulae, d’Arrest is known today chiefly for his role in the discovery of the planet Neptune, and for the periodic comet that bears his name-this comet, which he discovered in 1851, was last seen in October 1963 and is significant because its orbit is gradually getting larger through the action of some nongravitational force.

D’Arrest, whose father was an accountant of Huguenot descent, attended the Collège Français in Berlin before entering the University of Berlin in 1839. He was a promising graduate student, with half a dozen publications and a medal from the King of Denmark (for discovering the comet 1845 I), when Johann Gottfried Galle got permission from Johann Franz Encke, director of the Berlin Observatory, to look for the trans-Uranian planet predicted by Urbain Leverrier. D’Arrest volunteered to help, and suggested the star chart to use: Hora XXI of the Berliner Akademische Sternkarten, completed by Carl Bremiker but not yet published. The search was successful that same night (23 September 1846), owing in large part to the excellence of the chart, but in making the initial announcement Encke mentioned only his staff member Galle and himself; it was not until 1877 that Galle set the record straight.

In 1848 d’Arrest was elected a foreign associate of the Royal Astronomical Society of London and chosen to fill a new post at the Leipzig observatory, where he worked under August Ferdinand Möbius—whose daughter he subsequently married. He received his Ph.D. degree from the University of Leipzig in 1850, and in 1851 published his first book, Ueber das System der kleinerer Planeten zwischen Mars und Jupiter, a study of the thirteen asteroids then known. His interest in comets and asteroids continued, as shown by his discovery of two more comets(1851 II, mentioned above, and 1857 I) and of the asteroid (76) Freia in 1862, but now d’Arrest began the studies of nebulae for which he received the Gold Medal of the Royal Astronomical Society in 1875.

Although many nebulae had already been observed, notably by William Herschel and his son John, their nature and particularly their distances were still unknown. To improve the situation d’Arrest made, and published in 1857, accurate measurements of the positions and appearances of two hundred and sixty-nine selected nebulous objects; after he became, in 1858, professor in the University of Copenhagen and director of its new observatory, he extended these observations to 1,942 nebulae, published as Siderum nebulosorum observationes Hafniensis 1861–1867, but gave up this approach when he realized that even those nebulae bright enough to be detected by his eleven-inch telescope were too numerous for any one man to observe in a lifetime.

Just before his untimely death d’Arrest began spectroscopic observations, following the lead of Sir William Huggins, and was the first to point out, in 1873, that the gaseous nebulae (those with bright line spectra) were preferentially located near the plane of the Milky Way and therefore probably relatively nearby objects in our own galaxy.

BIBLIOGRAPHY

I. Original Works. D’Arrest’s discovery of comet 1845 I was announced in the “Cometen-Circular” of the Astronomische Nachrichten, 22 (1845), cols. 343–344, and the orbit he calculated for it was published in a letter to the editor written by Encke, ibid., 23 (1846), cols. 81–82. His early publications included three letters to the editor, on Colla’s comet of June 1845: ibid., cols. 231–234, 275–278, and 349–352; “Bestimmung der Elemente der Astraea, mit Rücksicht auf die Störungen aus der ganzen Reihe der Beobachtungen,” ibid., 24 (1846), cols. 277–288; “Elemente und Ephemeride der Astraea. 1846–47,” ibid., cols. 349–358; and “Ueber die Bahn des vom Dr. Peters entdeckten Cometen,” ibid., cols. 387–390.

During his stay in Leipzig d’Arrest’s publications included: “Neue Verbesserung der Elemente der Hygiea-Bahn,” in Berichte über die Verhandlungen der königlich sächsischen Gesellschaft der Wissenschaften, 2 (1850), 1–9; “Nachricht von der Entdeckung und den ersten Beobachtungen des Planeten Victoria, des Cometen von Bond und des dreizehnten Hauptplaneten,” ibid., 105–108; “Über die Gruppirung der periodischen Cometen,” ibid., 3 (1851), 31–38; the discovery of comet 1851 II [comet d’Arrest] in the “Cometen-Circular” of Astronomische Nachrichten, 32 (1851), cols. 327–328, with further observations of it in cols. 341-342 ; Ueher das System der kleineren Planeten zwischen Mars und Jupiter (Leipzig, 1851); “Resultate aus Beobachtungen der Nebelflecken und Sternhaufen. Erste Reihe,” in Abhandlungen der mathematisch-physischen Classe der königlich sächsischen Gesellschaft der Wissenschaften, 3 (1857), 293–377, with errata on 378; and his discovery of comet 1857 I, announced in the “Cometen-Circular” of Astronomische Nachrichten, 45 (1857), cols. 223–224, with more observations in cols. 253–254 and 365–368.

While in Copenhagen d’Arrest’s works included the discovery of asteroid (76) Freia, announced in Astronomische Nachrichten, 59 (1863), cols. 16–17, with further observations and orbital elements in cols. 77–78 and 91–92; Siderum nebulosorum observationes Havnienses institutae in secula universitatis per tubum sedecimpedalem Merzianum, ab anno 1861 ad annum 1867 (Copenhagen, 1867); “Om Beskaffenheden og Ubbyttet af de spektral analytiske Undersogelser indenfor Solsystemet, sete i forbindelse med Kometernes Udviklingshistorie,” in Forhandlingerne ved de Skandinaviske Naturforskeres (1873), 145–161; and a letter to the editor concerning the location of gaseous nebulae, in Astronomische Nachrichten, 80 (1873), cols. 189–190.

There is a list of 127 papers by d’Arrest in the Royal Society of London’s Catalogue of Scientific Papers: I (London, 1867), 101–103; VII (London, 1877), 49–50; IX (London, 1891), 72; and XII (London, 1902), 24. A number of additional items can be found among the more than 400 entries under d’Arrest’s name in the cumulative indices to Astronomische Nachrichten:21–40 (Hamburg, 1856), 123–128; 41–60 (Hamburg, 1866), 122–124; and 61–80 (Leipzig, 1875), 80–81.

II. Secondary Works. An address delivered by the president of the Royal Astronomical Society, John Couch Adams, when d’Arrest received—in absentia—that society’s Gold Medal, was printed in Monthly Notices of the Royal Astronomical Society, 35 (1875), 265–276, and gives a contemporary evaluation of his accomplishments. For further details on his life, see the biographical memoir by John Louis Emil Dreyer in Vierteljahrsschrift der Astronomischen Gesellschaft, 11 (1876), 1–14 and an unsigned obituary in Monthly Notices of the Royal Astronomical Society, 36 (1876), 155–158.

The discovery of the planet Neptune was announced by Encke, in a letter to the editor dated 26 Sept. 1846, that appeared in Astronomische Nachrichten, 25 (1847), cols. 49–52. The first printed mention of d’Arrest’s contribution was in Dreyer’s memoir (see above); Galle’s first public acknowledgment of the part played by d’Arrest in this discovery was “Ein Nachtrag zu den in Band 25 und dem Ergänzungshefte von 1849 der Astr. Nachrichten enthaltenen Berichten über die erste Auffindungen des Planeten Neptun.” in Astronomische Nachrichten, 89 (1877), cols. 349–352. In his “Historical Note Concerning the Discovery of Neptune,” published in Copernicus, 2 (1882), 63–64, Dreyer called attention to this paper by Galle, remarking upon the fact that neither Encke nor Galle had previously seen fit to give proper credit to d’Arrest. Galle agreed to the justice of this rebuke in “Ueber die erste Auffindung der Planeten Neptun.” ibid., 96–97.

Sally H. Dieke