sentences:  After earning a bachelor's degree, he returned to Arnhem in 1871 to teach night school classes in mathematics, but he continued his studies in Leiden in addition to his teaching position.In 1875, Lorentz earned a doctoral degree under Pieter Rijke on a thesis entitled """" (On the theory of reflection and refraction of light), in which he refined the electromagnetic theory of James Clerk Maxwell.On 17 November 1877, only 24 years of age, Hendrik Antoon Lorentz was appointed to the newly established chair in theoretical physics at the University of Leiden.