STøRMER, FREDRIK CARL MüLERTZ

(b. Skien, Norway, 3 september 1874; d. Oslo, Norway, 13 August 1957)

mathematics, geophysics.

Størmer’s father, Georg Størmer, was a pharmacist; his mother was the former Elisabeth Mülertz. When he was twelve, the family moved to Oslo (then Christiania). As a young boy he was interested in botany, which remained a lifelong hobby. During his high school years, Størmer’s interest and ability in mathematics became apparent; and through a friend of the family, who was a professor of mathematics at the University of Oslo, he received instruction in that science. His first publication was published while he was still in high school (1892). Størmer entered the University of Oslo in 1892, received the master’s degree in 1898, and was awarded the doctorate in 1903. In the latter year he became professor of pure mathematics, a post he held until his retirement in 1944.

Størmer’s first papers were on number theory; but in 1903 he met the physicist Kristian Birke-land, who studied the polar aurora. Birkeland approached the problem experimentally, by bombarding a magnetic sphere in a vacuum with cathode rays. In this way it was possible to observe phenomena resembling the polar aurora. Størmer made the field observations and the theoretical calculations of the charged particles. The observations of the polar aurora were made photographically, by taking parallactic pictures along a base line. Størmer thus accumulated an enormous amount of observational material, not only on the altitude but also on the size, shape, and periodicity of the polar aurora. In the course of this work he also acquired interesting information on noctilucent and mother-of-pearl (nacreous) clouds. He constructed the instruments and worked out the procedures for these observations himself, showing a gift for experimentation that is rare among pure mathematicians.

Størmer’s other approach to the study of the polar aurora was a mathematical analysis of the trajectories of charged particles in the earth’s dispole magnetic field. It included the numerical integration of series of differential equations–an enormous task before the advent of electronic computers–in which Størmer was assisted by many of his students. His analysis showed that only some trajectories are possible, others being “forbidden.” Størmer was also led to postulate a circular electric current in the equatorial plane of the earth and showed that electrons may be trapped into oscillatory trajectories in the earth’s dipole field. Although his calculations were made in the course of studying the polar aurora, they became important for other areas of cosmic geophysics. When the latitudinal variation in cosmic radiation was discovered in the 1930’s, it could be explained by Størmer’s calculations; and the discovery of the Van Allen belts confirmed, to a surprising degree, his theoretical analysis of the trajectories of charged particles from the sun in the dipole field of the earth.

Størmer was an old-fashioned scientist who worked by himself. He mastered the field and often did the manual labor connected with his experiments and calculations. His last book, The Polar Aurora (1955), is not only his final summary, but also an up-to-date and authoritative study. Størmer had no direct followers; but he exerted a profound influence during his forty-one-year teaching career. He also was an excellent popularizer.

BIBLIOGRAPHY

Most of Størmer’s scientific publications appeared in the Norske Videnskabsakademiets Skrifter; lists can be found in Årbok. Norske videnskapsakademi i oslo (1892–1953). His books include Fra verdensrummets dybder til atomenes indre (Oslo, 1923), which went through 4 eds. in Norwegian and was translated into 5 foreign languages; and The Polar Aurora (Oxford, 1955).

An obituary is L. Harang, “Minnetale over professor Carl Størmer,” in Årbok. Norske Videnskapsakademi i Oslo (1958), 81–85.

Nils Spjeldnaes