ZöLLNER, JOHANN KARL FRIEDRICH

(b. Berlin, Germany, 8 November 1834; d. Leipzig, Germany, 25 April 1882)

astrophysics.

Züllner’s father was a patternmaker and later a cotton printer. Although Züllner had displayed outstanding talent for constructing instruments and conducting experiments by the age of sixteen, the death of his father (1853) obliged him to take over the direction of his factory. But Zöllner was not temperamentally suited to a business career: and shortly after assuming that post, he gave it up and resumed his education. He failed the final secondary-school examination, however, because of his poor marks in languages. In 1885 he began to study physics and other sciences at the University of Berlin, where his teachers included H. G. Magnus and H. W. Dove. While still a student Zöller published “Photomertrische Untersuchungen” in Poggendroff’s Annalen der Physick und Chemie. He also worked on developing electric motors; but considering the great success later achieved in this area by Werner von Siemens, Zollner’s efforts proved to be of li9ttle significance.

Zöllner erected a small private observatory in the towner of his father’s factory in Schöneweide (now part of Berlin), and thus was able to test his ideas concering the photometry of celestial bodies. In 1857 Zöllner went to Basel, where his teachers included G. H. Wiedemann. He receive3d the Ph. D. in 1859 for a work on photometric problems: “Photometrische Untersuchungen, insbesondere über die Lichtentwickelung galvanisch glühender Plantindrähte.”

Exploiting a chance observation that he had made at Basel, Zöllner invented the astrophotometer, which was constructed in the Kern optical and mechanical workship in Aarau. (The accompanying drawing illustrates the instrument’s operating principle.) Using this instrument, he investigated fundamental problems of photometry, made critical comparisons of other photometers, and soon

amassed a considerable body of material. On the advice of Mitscherlich and Wiedemann, Zöllner decided to compete for a prize offered by the Vienna Academy of Sciences. The jury found that Zöllner had not measured the brightness of enough stars to receive the prize. (The other two papers submitted were also found not to merit the prize, and thus none was awarded.) Zöllner’s eatry, which he published in 1861, is a classic of astron physics. The photometer described in it far surpassed all its presecessors and, in a modified form, found wide application. The Potsdam observatory used it to obtain data unsurpassed precision for its Photometrische Durchumusterung des nördlichen Himmels, the publication of which was begun at Zöllner’s suggestion.

In 1862 Zöllner moved to Leipzig and published Photometrische Studien mit besonderer Rücksicht auf die physische Beschaffenheit der Himmelskörper (1865), whcih contains his Habilitationsschrift, “Theorie der relativen Lichtstärken der Mondphasen.” With his appointment as professor at the University of Leipzig in 1866, Zöllner’s financial situation was sufficiently improved for him to resume important experimental research.

Among Zöllner’s main achievements was the design of the reversion spectroscope (1869), another instrument that demonstrates his experimental ingenuityt. It is based on the principle of the heliometer: two beams of rays are conducted through two direct-vision prism systems arranged so that the dispersion within them occurs in mutually opposed directions. With this device Zöllner intended to improve the precision of measurement of Doppler shifts in the spectra of objects with velocities having a high radial component. Hermann Vogel used the instrument to determine the rotational velocity at the solar equator. The reversion spectroscope later lost its importance with the adoption of more exact methods.

Another important device designed by Zöllner is the horizontal pendulum, which in improved form was widely used in geophysical research. Inspried by the attempts of Janssen and Lockyer to observe solar protuberances, Zöllner devised the first method that made these phenomena easily amenable to study. These inventions, which make Zöllner a pioneer in astrophysics, brought him membership in the Saxon Academy of Sciences at Leipzig.

Zöllner also made an intensive study of theoretical questions, including solar theory, sunspots, and solar rotation, and Olber’s paradox. One product of these rather speculative inquiries was especially important for the development of spectroscopy, the memoir “Über den Einfluss der Dichtigkeit und Temperatur auf die Spektra glöhender Gase” (1870). Also of far-reaching significance was Zöllner’s theory of comets, in which he correctly assumed that elements of the nucleus of a comet gradually vaporize as it nears the sun. Beyond this, the book on comets contains a wealth of penetrating remarks on the subject announed in the subtitle Beiträge zur Geschichte und Theorie der Erkenntnis This portion of the book is notable for a number of at least partly original ideas and critical comments. Attacking abuses in the scientific profession of his time, Zöllner lashed out with great vehemence against the vantity of scientists, ridiculing scientific careerism and contending that these vices are harmful to the progress of science.

Zöllner continued this polemic in such work sas Das deutsche Volk und seine Professoren. Eine Sammlung von Citaten ohne Kommentar (Leipzig, 1880). The scientific community responded with counterattacks, and there began a long period of controversies that drove Zöllner into ever greater isolation. The excessive irony and somewhat biased approach of whcih he was guilty were, however, only partiaally responsible for this isolation. In 1875 Zöllner had met William Crookes in London and begun an intensive study of Spiritualism, to which he ultimately became a convert. In the following years some scientists did not hesitate to attribute Zöllner’s views to an increasingly serious mental illness. Even sympathetic friends, such as Otto Struve, were much dismayed by his adherence to this doctrine, and W. Foerster termed this change in his life both remarkable and painful. Zöllner, however, refused to be dissuaded from pursuing his unscientific speculations ; and he saw in his supposed proofs of the existence of a “transcendental world” a support for theology . In the last years of his life he produced little work of scientific significance . He died-presumably of a stroke-while preparing the preface to the third edition of his book on comets.

BIBLIOGRAPHY

I. Original Works. A full list of Zöllner’s major works can be found in F. Koerber, Zöllner, 106-107 (below). The papers by Zöllner in the Astronomische Nachrichten are cited in Generalregister der Bände 41-80 der Astronomischen Nachrichten, H. Kobold, ed. (Kiel 1938), col. 118; and in Generalregister der Bande 81-120 der astronomischen Nachricten, A. Krueger, ed. (Kiel, 1891), col. 132. Zöllner collected his most important shorter works as Wissenschaftliche Abhandlugen, 4 vols (Leipzig, 1878-1881).

II. Secondary Literature. See W. Foerster, Lebenserinnerungen und Lebenshoffnungen (Berlin, 1911), 95-98; D. B. Herrmann, “Karl Friedrich Zöllner und die ‘Potsdamer Durchumusterung,’” in Sterne, 50 (1974), 170-180; and “Ein eignehädiger Lebenslauf von Karl Friedrich Zöllner aus dem Jahre 1864,” Mitteilungen der Archenhold-Sternwarte Berlin-Trepton,97 (1974); R. Knott, “Zöllner,” in Allgemeine deutsche Biographie, XLV (Leipzig, 1900), 426-428; F. Koerber, Karl Friedrich Zöllner (Berlin, 1899), no. 53 of Sammlung Populärer Schriften, edited by the Gesellschaft Urania, Berlin; S. (probably W.Scheibner), “Todes,-Anzeige,” in Astronomische Nachrichten,102 (1882), cols. 175-176; and M. Wirth. Friedrich Zöllner. Ein Vortrag mit Zöllners Bild und Handschrift (Leipzig, 1882).

Dieter B. Herrmann