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In the early 1930s, he became a friend and colleague of Mortimer Graves, of the American Council of Learned Societies. Graves and Hummel worked not only to build the Library of Congress collection but to promote the study of Asia in colleges and universities across the country. J.J.L. Duyvendak, of Leiden University in the Netherlands, met Hummel and encouraged him to turn his longtime interest in the Chinese scholar Gu Jiegang into a serious study of the New Culture Movement's revisionist scholarship on ancient Chinese history. Hummel did so, and his dissertation, "The Autobiography of a Chinese Historian" earned him the PhD degree from the University of Leiden in September 23, 1931.