Complex sentence: He was appointed as a professor of mathematics in 1903, a position he held for 43 years; after he received a permanent position in Oslo, Størmer published his subsequent writings under a shortened version of his name, Carl Størmer.
Split into simpler sentences: He was appointed as a professor of mathematics in 1903, a position he held for 43 years. After he received a permanent position in Oslo, Størmer published his subsequent writings under a shortened version of his name, Carl Størmer.