Kayser, Heinrich Johannes Gustav

(b. Bingen, Germany, 16 March 1853; d. Bonn, Germany, 14 October 1940)

physics.

Kayser was the son of Heinrich Kayser, a former lord of the manor, and the former Amelie von Metz. He attended the pädagogium in Halle and the Sophie Gymnasium in Berlin, where he received a diploma on 4 March 1872. After a year of traveling Kayser studied from April 1873 until March 1879 in Strasbourg, Munich, and Berlin, mainly with Kundt, Helmholtz, and Kirchhoff. On 13 March 1879 he graduated as Ph.D. with the thesis “Der Einfluss der Intensität des Schalles auf seine Fortpflanzungsgeschwindigheit.”

In the previous year Kayser, initially together with Heinrich Hertz, had become assistant to Helmholtz at the Berlin Physical Institute. He remained there until the fall of 1885. On 26 September 1881 he gained qualification as academic lecturer with the dissertation “Über die Verdichtung von Gasen an Oberflächen in ihrer Abhängigkeit von Druck und Temperatur.” In 1885 he was appointed professor of physics at the Hannover Technical University. Here, working with Carl Runge, he began his investigations in the field of spectroscopy. In his Handbuch der Spektroskopie (1900) he described the purpose of his investigations:

It is certain that the light is produced by the motions of the molecules or of the particles or of their electrical charges. It was expected that chemical elements would be similar to a certain extent in the structure of their spectra according to their periodic classification, Balmer was the first who derived a real result of regularity in the distribution of the wave numbers of the spectral lines of hydrogen. It was hoped that similar laws would be detected for other elements.

Kayser and Runge began these investigations at about the same time that Rydberg began working along the same lines. Kayser and Runge determined the spectra anew, using a Rowland concave grating, and found the results to be much more reliable from this method; Rydberg evaluated the existing older measurements anew. The investigations showed that for many elements a regular structure could indeed be demonstrated. For the alkali metals (lithium, sodium, potassium, rebidium, cesium), all known spectra lines could be settled at three series described very accurately by equations of the same structure; these formulas were also interrelated. Furthermore, an important relation between the atomic weight and the structure of the spectra was discovered. Kayser and his co-worker learned not only that the spectra of these five related elements were ordered by the same plan, but also that they changed with perfect regularity, according to the increasing atomic weight.

Kayser and Runge next investigated, with similar results, the alkali earths and also some metals of the groups IB and IIB of the periodic table of elements. The regularity was not so perfect in this case, however. Kayser said that the number of irregular lines grows as one proceeds in the natural system of elements. He emphasized that the formulas he and his associate had found in Hannover, as well as those of Rydberg, were only empirical and far from the discovery, through the structure of the spectra, of the behavior of the atoms. In his criticism of Rydberg, Kayser was always willing to acknowledge the merits of Rydberg’s work. From the vantage of today, the work of Rydberg and of Kayser and Runge was indispensable to the atomic theory brought forth twenty-five years later by Rutherford and Bohr. Although Kayser provided the solid experimental foundation for this theory with his experiments—he was the experimenter, Runge the theorist—Rydberg, full of ideas and speculations, was more successful in formulating the spectra equations; hence the name Rydberg constant. Nevertheless, Kayser and Runge’s lists of the exact frequencies of many spectral lines guarantee their place in the history of science.

Kayser and Rydberg also collaborated in the discussion with Pickering concerning the spectrum of ζ Puppis. The latter discovered there some spectral lines very near to the Balmer series. Bohr was later able to explain that these lines are produced by ionized helium. At the end of the nineteenth century, the lines occurring in O stars were attributed to hydrogen and called protohydrogen.

In 1894 Kayser was appointed successor to Heinrich Hertz as professor of physics at the University of Bonn, at this time an outstanding professorial chair for this discipline. During Kayser’s tenure, the Institute of Physics in Bonn became a center of spectroscopic investigations, and Kayser obtained a new and modern building after more than a decade. Previous to his retirement, Kayser wrote his Handbuch der Spektroskopie, comprising eight volumes. Although he was greatly interested in astrophysics, the field is not treated in this work. Even today, the Handbuch is a remarkably comprehensive achievement for a single author, compiling countless facts and aspects of spectroscopy beginning with Newton. The first astrophysical investigations by Kayser were of spectra of comets and variable stars. He later published his ideas concerning the temperature of stars, and was one of the first to attempt an explication of novae in terms of radiation processes (1912). In addition to teaching, he wrote a textbook for students which had several editions.

Kayser was a member of the International Union for Solar Research and an honorary member of the Royal Institution of Great Britain, and he belonged to several foreign academies. In 1912 he received an honorary doctorate of jurisprudence from the University of St. Andrews. He had widespread interests in different fields, notably in Greek and Roman art, and he made excellent photographs during journeys to Italy and Greece. In 1887 Kayser married Auguste Hofmann, surviving her by nearly twenty-five years.

BIBLIOGRAPHY

Kayser’s original works include Lehrbuch der Spektralanalyse (Berlin, 1883); “Spektren der Elemente,” in Abhandlungen der Konigl. Preussischen Akademie der Wissenschaften in Berlin (1888–1893), written with Carl Runge; “Die Dispersion der Luft,” ibid. (1893), written with Runge; “Bogenspektren der Elemente der Pb-Gruppe,” ibid. (1897); Handbuch der Spektroskopie, 8 vols. (Leipzig, 1900–1932), vols. VII and VIII written with Heinrich Konen; and Lehrbuch der Physik für Studierende (Stuttgart, 1890; 6th ed., 1921). See also various articles by Kayser in Astronomische Nachrichten, 134 (1894), 135 (1894), 162 (1903), 191 (1912); and Astrophysical Journal, 1, 4, 5, 7, 13, 14, 19, 20, 26, 32, 39 (1895–1914).

For obituaries see R. Frerichs, in Naturwissenschaften, 29 (1941), 153–155; F. Paschen, in Physikalische Zeitschrift, 41 (1941), 429–433; and H. Crow, in Astrophysical Journal, 94 (1941), 5–11.

H. C. Freiesleben