**Carl Størmer**'s parents were Henrietta Mülertz and Georg Ludvig Stormer. Georg Stormer was a dispensing chemist working in Skien at the time that his son was born but later the family moved to Oslo. Carl was his parents' only child [2]:-

From his childhood he showed a deep interest in the natural sciences, astronomy, physics, chemistry, meteorology, geology and in particular botany. At the age of about sixteen his interest turned exclusively to pure mathematics.

Størmer entered the University of Christiana (as Oslo was then called) in 1892. He studied there until 1897 and in the following year he obtained the candidates degree (about equivalent to a doctorate but without the accompanying title). In 1899 he was awarded a five year fellowship which enabled him to continue his studies abroad for, by this time, he was in Paris. He spent two academic years, from 1898 to 1900, at the Sorbonne studying with Émile Picard, Henri Poincaré, Paul Painlevé, Camille Jordan, Gaston Darboux, and Édouard Goursat. After returning to Olso, he went abroad again to spend 1902 at Göttingen in Germany. He married Ada Clauson in 1900; they had five children, three boys and two girls.

It is unusual for anyone to publish a paper in the year they enter university as an undergraduate, but this is exactly what Størmer did with a paper on the summation of trigonometric series. By 1896, still a year before the award of his candidates degree, he had not only written seven mathematical papers but they were already in print by this time. Even more unusual is the fact that by this time he had also published a number of short notes on botany. His output of mathematical papers continued with twelve papers on series, number theory, and the theory of functions between 1896 and 1902. He worked with Sylow and Holst to produce two volumes to celebrate the centenary of Abel's birth in 1902. One volume was in Norwegian, the other a translation into French. In the same year he also published papers by Abel which he had left unpublished at his death, giving both Norwegian and French versions. Yet another work which came out in 1902 was a posthumous paper of Sophus Lie, edited by Størmer and Guldberg.

Given this remarkable output of important mathematical works, it is no surprise that in 1903 he was appointed as professor of pure mathematics at the University of Oslo. It was a post that Størmer held until 1946 yet, although he did continue to publish the occasional pure mathematics paper during this period, his interests were diverted by a different topic. Before looking at his new interest, however, we should comment briefly on his other work in pure mathematics. After his appointment as professor, he published, as he had earlier, a number of historical documents and some historical articles. He also published some elegant papers on number theory which were highly praised by Mordell.

Birkeland, one of Størmer's colleagues, had put forward a theory in 1896 that auroras were caused by electrons emitted by the sun which interacted with the earth's magnetic field. Poincaré had, in the same year, solved the differential equations resulting from the motion of a charged particle in the field of a single pole. This, of course, was not the situation for an aurora since the magnetic field of the earth is a dipole. This then was the problem that Stormer attacked [2]:-

Over many years[Størmer]made or organised such calculations, finding a great variety of orbits. His papers on this subject constitute a major part of his life's work; they number at least48. Many are short, and in several cases he published brief accounts of the same work in different languages and journals. But many of the papers are very substantial in length and content.

A summary of all of this work appeared in Størmer's book *The polar aurora* published in 1955. However, this is not simply a theoretical investigation. As Størmer explained in the Preface to the work, he [2]:-

... found it necessary to obtain more facts about the auora in order to compare theory and observation. A photographic method designed to determine, among other things, the height and position of aurora was therefore developed and successfully applied. The chief results obtained from the analysis of a vast number of parallactic photographs are discussed in this book.

Certainly Størmer was not the first to photograph an aurora. This was first achieved in 1892. However he was the first to undertake a systematic scientific photographic investigation which he began in 1909 and continued throughout his career. It was not his interest in aurora which led him towards photography, rather his interest in photography came from his youth. As he wrote in the Preface we just quoted from:-

It might be a source of interest to many to observe, in the development of my photographic work, what may result when a pure mathematician happens to be an enthusiastic amateur photographer.

Størmer's interest in photography went much further [2]:-

... he applied his skill in photography(unsuspected by the subject)to obtain pictures ... of many celebrities of Oslo of those days. Long afterwards, when he was nearing the age of70, these photographs formed the subject of an exhibition in Oslo.

He also published two works in 1942 and 1943 giving an illustrated account of his 'snapshots of famous people of the last fifty years'.

Chapman, who knew Størmer for nearly 40 years, describes him in [2] as:-

... a rather large and bulky slow-moving man. ... He liked the pleasures of the table, good food and wine; he liked the theatre and the opera, and took with him opera glasses the better to observe the action and the danseuses.

Størmer was honoured in many ways: he was elected to several Scandinavian academies, the Royal Society of London and the Paris Academy of Sciences. He was given honorary degrees by the universities of Oxford, Copenhagen and the Sorbonne. The Paris Academy of Sciences awarded him their Janssen Medal in 1922. He was invited to give a one-hour lecture on *Modern Norwegian Researches on the Aurora Borealis* to the International Congresses of Mathematicians in Toronto in 1924 and he was president of the International Congresses of Mathematicians in Oslo in 1936.

**Article by:** *J J O'Connor* and *E F Robertson*