sentences:  He then became a professor at Zhejiang University and served as head of the Department of Physics there from October 1936 to 1950.After the Marco Polo Bridge Incident in July 1937, the Japanese invasion of China forced Wang and other professors to retreat with all the faculty of Zhejiang University to the western mountainous rural areas of China to escape capture.Despite the difficult conditions, he nonetheless tried in 1939 to find evidence of tracks of nuclear fission caused by neutron bombardment of cadmium acid on photographic film.