Abraham Pais

I introduce the subject of fine structure with a mini-calendar of events. ...Winter 1914-15. Sommerfeld computes relativistic orbits for hydrogen-like atoms. Pashcen, aware of these studies, carefully investigates fine structures, ....January 6, 1916. Sommerfeld announces his fine structure formula, citing results to be published by Paschen in support of his answer.February 1916. Einstein to Sommerfeld: "A revelation!"March 1916. Bohr to Sommerfeld: "I do not believe ever to have read anything with more joy than your beautiful work."September 1916. Paschen publishes his work, acknowledging Sommerfeld's "indefatigable efforts.