Complex sentence: In April 1936, President Coching Chu of Zhejiang University invited him to return to that institution, where, in August 1936, Shu was promoted to the rank of associate professor, then in 1937, professor.
Split into simpler sentences: In April 1936, President Coching Chu of Zhejiang University again invited him to come back. In August 1936, Shu was promoted to associate professor, and in 1937, professor.