Early in his course he began to lay particular stress on Practical Physics, to which he was devoted throughout his career. He held six different scholarships in Physical Science, including an 1851 Exhibition Scholarship and a Carnegie Fellowship.
For two years he was Assistant to Professor MacGregor in the Physical laboratory, and from 1909 he spent two sessions in the laboratory of Professor Des Coudres in the University of Leipzig. A family bereavement necessitated his return to Edinburgh, where he continued his research for two years. Early experiments at Professor Chrystal's suggestion led to papers with Peter White on "Some Experimental Results in connection with the Hydrodynamical Theory of Seiches" (Proc. R.S.E., 1906) and with E M (Sir Ernest) Wedderburn on "Observations with a Current Meter in Loch Ness" (Proc. R.S.E., 1909). The Royal Society of Saxony published a paper on "The Volume of Waters at High Pressures and Temperatures" in 1911, and this was followed by "Isopiestic Expansibility of Water at High Pressures and Temperatures" (Proc. R.S.E., 1911), and "On the Compressibilities of Dilute Solutions of certain Inorganic Salts" (Proc. R.S.E., 1913). As Nichol Assistant and Demonstrator in Edinburgh University, he became highly esteemed for his experimental skill and initiative by Professor Chrystal, Dr Cargill G Knott, Professor Peddie, Professor MacGregor and Dr Carse, with whom he worked. Having qualified for the Schoolmaster's General Diploma and studied under Dr Morgan at the Provincial Training College, he turned his attention to teaching on his appointment as Head of the Physics Department in the Heriot-Watt College in 1912. From that time until his retiral in 1944 he was fully engaged in training a long line of engineers, chemists and others in day and evening classes. Under his direction a great expansion of the work of the Department took place, and, with the exception of Specialised Optical Courses, the main activities of the Physics Department were in connection with the fundamentals of Physics for students in the technological departments. At his appointment the Department was in its infancy, having until two years previous formed a section of Electrical Engineering and Physics under Professor F G Baily. New and improved laboratories were provided with the extension of the College in 1937, but the advent of war proved a serious check in the normal academic courses, and the training of service units in a long succession of courses made serious calls on all departments until Watson's retiral. Throughout his career he co-operated most effectively and harmoniously with all departments of the College, and was a valued friend and adviser to many students now holding responsible positions at home and abroad.
Although never enjoying robust health, Watson was a keen golfer, trained on the famous Musselburgh Links, and latterly, a skilled and enthusiastic bowler.
He was unmarried, and died on June 28, 1952, after a long period of illness.
He was elected a Fellow in 1923.