In 1897 Beattie was appointed as Professor of Applied Mathematics and Experimental Physics at the South African College in Cape Town. Beattie's research included the influence of X-rays, ultra-violet light, and the rays from uranium on the electrical conductivity of gases, and the leakage of electricity from charged bodies at moderate temperatures. During the Anglo-Boer War in February 1899, he and others demonstrated the application of wireless telegraphy by transmitting signals over a distance of 120 metres on Cape Town's Grand Parade using equipment imported from Britain. In 1901 he began a magnetic survey of South Africa with Prof John Todd Morrison. Starting in 1908 he extended the survey through central Africa to Egypt, arriving in Cairo in December 1909.