Engineer, noted for his archaeoastronomical research on stone circles. Born at Carradale (Argyll and Bute), the eldest son of a farmer. The family moved to Dunlop (East Ayrshire) in 1901. Thom was educated at Kilmarnock Academy, the Royal College of Science and Technology (now the University of Strathclyde) and the University of Glasgow, where he lectured from 1922 to 1939. He worked in aeronautical engineering and is credited with building the first wind tunnel in Scotland. He worked at the Royal Aircraft Establishment, Farnborough, during World War II and was involved in testing the Spitfire fighter. Thom was elected to the Chair of Engineering Science at Oxford in 1945.
Thom was fascinated by prehistoric sites, particularly megalithic monuments, both in terms of their construction and design. He toured many in Britain and France, making detailed measurements and showed how they were astronomically-aligned serving as calendars for events such as midsummer, midwinter and the equinoxes. More controversially, he first suggested the 'megalithic yard' (0.83m) as a standardised prehistoric measurement. This was accepted by some but, despite voluminous data and detailed statistical analysis, was dismissed by mainstream scientists.
Thom received honorary degrees from both the Universities of Glasgow and Strathclyde. He died in Belford Hospital, Fort William. The Thom Building, home to the Department of Engineering Science at Oxford, is named in his honour.