The developing science departs at the same time more and more from its original scope and purpose and threatens to sacrifice its earlier unity and split into diverse branches.

Erster Band; Die gruppentheoretischen Grundlagen (in German) Leipzig: B. Annalen Bd. In the 1890s Klein turned to mathematical physics a subject from which he had never strayed far writing on the gyroscope with Arnold Sommerfeld.

Christian Felix Klein (25 April 1849 – 22 June 1925) was a German mathematician known for his work in group theory complex analysis non-Euclidean geometry and on the connections between geometry and group theory.