Galle, Johann Gottfried

(b. Pabsthaus, near Gräfenhainichen, Germany, 9 June 1812; d. Potsdam, Germany, 10 July 1910)

astronomy.

Galle was the son of J. Gottfried Galle and Henriette Pannier. He was born in an isolated house on the Dübener Heide, a wooded heath between the Elbe and the Mulde, where his father was manager of a tar distillery. He attended school at Radis, his mother’s birthplace. There the local clergyman prepared both one of his own sons and Galle for the secondary school at Wittenberg.

Galle was at Wittenberg from April 1825 until April 1830, when he went to study in Berlin. His teachers there included Hegel, Dirichlet, Dirksen, Dove, Ideler, and—most important—Encke, who was to be highly influential in his later career. In 1833 Galle was granted the facultas docendi to teach mathematics and physics at the Gymnasium level. He spent the required probationary year teaching at Guben and Berlin, where he was made assistant teacher at the Friedrich-Werder Gymnasium in March 1834. While he was teaching in secondary school, Galle kept in touch with Encke; and in 1835 Encke, who had become director of the Berlin Observatory (and had had it newly rebuilt to his own specifications), had Galle appointed to an assistantship that had been created especially for him.

Galle spent the next sixteen years at the observatory, where his duties concerned him largely with astrometry. He became in addition an avid observer of comets, including Halley’s comet in its appearance of 1835 (he was to live to see it again in 1910); the comet newly discovered by Boguslavsky; and Encke’s comet. In 1839 and 1840 Galle himself discovered, in quick succession, three new comets, and thus attracted the attention of experts in the field as well as royal recognition.

In 1836 Alexander von Humboldt invited Galle to participate in the computation of the astronomical material that he had collected during his journeys and thereby initiated a professional association that was to last fifteen years. During this same period, Galle again attended Encke’s lectures in order to further his theoretical knowledge, and Encke entrusted him with further computational work involving the minor planets, especially Pallas, which he had previously observed. In about 1839 Galle began to compute the ephemerides of this planet for the Berliner astronomisches Jahrbuch; he continued these calculations for thirty years. He made other computations of the elements and ephemerides of comets, including two of those that he had discovered. In 1838 he observed the crepe ring of Saturn, although he did not publish this discovery.

Having continued his theoretical studies, Galle wished to obtain the doctorate. The government gave him financial aid and he received the degree on 1 March 1845. His thesis, Olai Roemeri triduum observationum astronomicarum, was based upon unanalyzed data from three days of exceptionally good meridian observations made by the Danish astronomer in 1706. (Except for these three days, the contents of Roemer’s other valuable observations had been destroyed by fire.) Galle sent a copy of this thesis to Le Verrier, to whom he thought Roemer’s observations would be of value.

Le Verrier did not immediately acknowledge the receipt of Galle’s work, but when he did he also informed Galle of the presumed position of a planet beyond Uranus whose orbit he had computed from the perturbations of Uranus’ motion. He encouraged Galle to look for this planet, since he thought the telescopes available to him at the Paris observatory inadequate to this purpose. Galle began to look for the planet the same evening that he received Le Verrier’s letter; on 23 September 1846 he and d’Arrest, who was at that time studying in Berlin, searched the region cited, but without success. Galle had made no special preparations for his search, since the diameter given by Le Verrier seemed to be sufficient for recognizing the planet as such. Additional data were necessary, however; fortunately the Berliner akademische Sternkarten were being readied for publication and the chart covering the area of observation had just been printed. The chart was not yet available commercially, but Encke had a copy. Galle borrowed it, and described what happened next:

Returning with the chart to the telescope I discovered a star of the eighth magnitude—not at first glance, to tell the truth, but after several comparisons. Its absence from the chart was so obvious that we had to try to observe it. Encke, who had been informed of all the details, took part in the observation on the same night. We observed the star until early morning; but, despite all duplications of effort, we did not succeed in discerning a definite motion, although a trace of change in the required sense seemed to occur. Full of excitement, we had to wait for the evening of 24 September, when our research was also favored by the weather and when the existence of the planet was proved [Astronomische Nachrichten, 89 (1877). 349–352].

The planet was at first called “Le Verrier’s planet.” but its name was shortly thereafter changed to Neptune. The location of the hypothetical planet had been computed simultaneously by Le Verrier and by John Couch Adams, working at Cambridge. The Cambridge astronomers were not able to find the planet and a long controversy arose concerning the priority of its computation. The possession of the new Sternkarten was of great advantage to the observers in Berlin; it was in all probability Arago, a close friend of Humboldt’s, who knew of the chart and suggested to Le Verrier that help might be available. Both Le Verrier and Adams were aware that the time to search for the planet was ripe, despite the uncertainties inherent in their computations; possible errors in calculating both the mass and the distance of the undiscovered body disturbing Uranus would only be magnified at a later date. (It is interesting to note that Galle found Neptune less than one degree from where Le Verrier predicted it would be.)

Following the discovery of Neptune, Galle contributed observations and computations of a provisional circular orbit toward the further tracking of the planet. His modesty prevented him from capitalizing on his discovery, and it was Encke who reported in detail on it to the Berlin Academy and in the Astronomische Nachrichten (of which volume 23 contains several articles on Neptune, including some account of the theoretical work that preceded its discovery). Galle’s achievement was nevertheless widely hailed.

Galle continued to work in Berlin as Encke’s assistant—he was even referred to as his teacher’s mirror image. (Encke’s influence, indeed, is to be seen throughout Galle’s lifework.) Among other projects, Galle made numerous distance measurements of double stars and, in 1847, published a supplement to the new edition of Olbers’ Abhandlungen . . . die Bahn eines Kometen zu berechnen, a list of all comet orbits computed up to that time, with important emendations and references to the literature.

In June 1851 Boguslavsky died at Breslau and Galle was offered the post of director of the observatory and professor of the university there. It was not easy for him to decide to leave the well-equipped Berlin Observatory for a small, almost obsolete observatory situated in the very center of the provincial town, but he accepted the opportunity to do independent work. Galle stayed at Breslau for fortysix years; in 1874–1875 he performed the duties of rector of the university. He taught all aspects of astronometry and meteorology, but devoted much of his classroom activity (as well as his research) to studies of comets and planetoids. He was a vivid lecturer and attracted large audiences—as many as sixty auditors are recorded at one time.

The primitive equipment available at the Breslau observatory did not permit Galle to do any pioneer work. He did, however, often participate in astronomical-geodetical tasks for the Europäische Gradmessung; as late as 1885 and 1888, he took part in the determinations of longitude between Berlin and Breslau. He also continued to observe comets, although he was mainly concerned with meteors, a continuation of his work in Berlin. He had already found that there is a relationship between the meteor showers recorded over the centuries and the appearance of comets.

Galle therefore tried to compute the orbit of the Lyrid meteor shower around the sun and to demonstrate its connection with comet 1861 I, discovered by Biela. He proved that meteors were to be expected to attend the descending node of the comet’s orbit; his theoretical assumptions were confirmed by a great number of shooting stars as predicted on the night of 28 November 1872, establishing the relation between meteor showers and the decomposition of a parent comet. Galle continued these investigations, examining a variety of significant meteor appearances and computing the Cosmic orbits of such meteors, which he classified as often hyperbolic.

It is known from a notice in a newspaper that at this time Galle was also considering the possible existence of a planet between Mercury and the sun, a hypothesis repeatedly put forth by Le Verrier. He seems to have dismissed its likelihood, however, reasoning that such a planet of any notable magnitude would be visible during total solar eclipses or on other occasions. He also, in 1864, issued a new edition of Olbers’ Abhandlungen, this time including the orbits of 231 comets (in a supplement of 1885, he increased the number to 286).

Galle’s interest in the minor planets led him to propose in 1872 that corresponding data on these bodies, observed at a close approach to the earth, be used to determine the solar parallax. The oppositions of Mars and lower conjunctions of Venus, particularly its passages in front of the sun’s disk, had already been observed with this objective; but Galle, who was widely experienced in the observation of the larger planets, correctly stressed that observations of the planetoids should be free from systematic errors. Galle corresponded extensively with astronomers of leading observatories (particularly those in the southern hemisphere) on this proposal; his suggestions were adopted and a series of simultaneous observations of Flora were made. These showed close agreement with the values derived by Simon Newcomb from other measurements. Galle took active part in these observations; he also witnessed the great advance in the method he had designed that resulted from the discovery of the planetoid Eros, although he did not participate in the discovery itself.

As did many of his fellow astronomers, Galle made regular meteorological observations or had them made for him. As conditions for astronomical observations became worse at the Breslau observatory, he placed increasing emphasis on meteorological and even geomagnetic measurements. He conducted the latter from 1869 to 1897; these were considerably impaired, however, by the construction of a streetcar line near the university, started in 1893. Through these abortive observations Galle wished to examine the magnetism of the earth in relation to “northern lights and other terrestrial and even cosmic conditions.” He also published a series of papers on climatology and weather forecasting; he was convinced that accurate scientific forecasting had not yet become feasible. Further works that he published late in his life touched upon several minor matters in a variety of fields.

In 1857 Galle married C. E. M. Regenbrecht, the daughter of a professor from Breslau. She died in 1887. They had two sons, one of whom, Andreas, was for many years an astronomer and geodesist at Potsdam. Throughout his long life Galle received numerous honors, especially memberships in scientific societies all over the world. He attained the age of ninety-eight in good physical and mental health and exerted a great influence on several generations of German astronomers. In his eulogy of Galle, W. Foerster accurately summarized his pedagogical career: “Without the men trained in theory and computation at the Breslau school . . ., it would not have been possible to cope with the enormous amount of computational work that resulted in the last fifty years from the discovery of more than half a thousand small planets between the orbits of Mars and Jupiter.”

BIBLIOGRAPHY

I. Original Works. Poggendorff lists Galle’s major works. Many of his most important papers were published in Astronomische Nachrichten; these include “Einige Messungen des Durchmessers des Saturns,” in Astronomische Nachrichten, 32 (1851), 187–190; “Über den mutmasslichen Zusammenhang der periodischen Sternschnuppen des 24 April mit dem 1. Kometen des Jahres 1861,” ibid., 69 (1867), 33–36; “Sternschnuppenbeobachtungen in Breslau 27 Nov. 1872,” ibid., 80 (1873), 279–282; “Über die Berechnung der Bahnen heller und an vielen Orten beobachteter Meteore,” ibid., 83 (1874), 21–50; and “Nachtrag zu den in Band 23 der Astronomischen Nachrichten gegebenen Berichten über die erste Auffindung des Planeten Neptun,” ibid., 89 (1877), 349–352.

Individual works include Grundzüge der schlesischen Klimatologie (Breslau, 1857); Über die Verbesserung der Planetenelemente (Breslau, 1858); Über eine Bestimmung der Sonnenparallaxe aus korrespondierenden Beobachtungen des Planeten Flora (Breslau, 1875); and Mitteilungen der Königlichen Universitáts-Sternwarte Breslau über hier bisher gewonnene Resultate für die geographischen und klimatologischen Ortsverháltnisse (Breslau, 1879).

II. Secondary Literature. Works on Galle and his work are W. Foerster, “J. G. Galle,” in Vierteljahrsschrift der Astronomischen Gesellschaft, 46 (1911), 17–22; and D. Wattenberg, J. G. Galle (Leipzig, 1963).

H. C. Freiesleben