Simplify the following text for a Grade 9 native English-speaking person.
Original: Bragg was appointed Quain Professor of Physics at University College London in 1915 , but did not take up his duties there until after World War I.
Simplified: Bragg was appointed Quain Professor of physics at University College London in 1915 , but did not take up his duties there until after World War I. While Quain professor at London he continued his work on crystal analysis .