Alfred Bull became a member of the Cape Astronomical Society in 1916, when it was being revived after the suspension of its activities as a result of World War I (1914-1918). He was a jovial person who served as the society's librarian for several years. When funds were low he paid some of the society's expenses out of his own pocket. These donations, made anonymously, included the binding cost of the society's set of volumes of the British Astronomical Association's Journal. After the society amalgamated with its counterpart in Johannesburg to form the Astronomical Society of South Africa in 1922 he continued as a member of the Cape Centre of the new society.
Bull delivered several papers at the monthly meetings of the Cape Astronomical Society. He was particularly interested in the scintillation of the stars and in one of his papers described his own observations and ideas on this topic. His paper "On the observation of sunspots with the sun at low altitudes" was read in 1921. Other papers by him dealt with Neptune and with the zodiacal light.