In 1923, Dirac graduated, once again with first class honours, and received a £140 scholarship from the Department of Scientific and Industrial Research. Along with his £70 scholarship from St John's College, this was enough to live at Cambridge. There, Dirac pursued his interests in the theory of general relativity, an interest he had gained earlier as a student in Bristol, and in the nascent field of quantum physics, under the supervision of Ralph Fowler. From 1925 to 1928 he held an 1851 Research Fellowship from the Royal Commission for the Exhibition of 1851. He completed his PhD in June 1926 with the first thesis on quantum mechanics to be submitted anywhere. He then continued his research in Copenhagen and Göttingen. In the spring of 1929, he was a visiting professor at the University of Wisconsin–Madison.