William Reid was a prominent South African amateur astronomer during the early part of the twentieth century, residing in Cape Town. He was one of the founders of the Cape Astronomical Association in November 1912 and a member of its first committee. He directed the association's Meteor Observing Section, formed in 1913, as well as the Variable Star Section, formed in March 1914. Following the disruption caused by the outbreak of World War 1 (1914-1918), the association was revived in 1916, with Reid serving as vice-president. By this time he was an assiduous searcher for comets and in 1917 was appointed to direct the Comet Section, while the Variable Star Section was taken over by John F. Skjellerup*. In 1917 he purchased a 150 mm refracting telescope and ten years later published a paper on 'Amateur observations with a six-inch telescope' (Journal of the Astronomical Society of South Africa, 1927, Vol. 2(2), pp. 39-52). After three years of searching he discovered his first new comet, followed later by several others. In March 1920 he made the historical observation, with C.L.O'B Dutton and D.G. McIntyre*, of the visible passage of a star behind all the rings of Saturn. The observation was at first received with scepticism in Britain, but was found to be beyond dispute.
When the Cape Astronomical Association amalgamated with its counterpart in Johannesburg to form the Astronomical Society of South Africa in 1922, Reid was elected a member of the first council, served as president of the society for 1925/6, and was the director of the Comet Section until his death in 1928. In 1925 he published an article on 'Comet hunting' in the society's Journal (Vol. 1(5), pp. 133-138). His contributions to comet work brought the society into international prominence. Early in 1928 he received the Jackson-Guild Medal of the Royal Astronomical Society for his comet observations, having discovered six new comets over the years. The Meteor Section he had started in 1913 failed because of lack of support, but in 1922 it was revived and directed by D.G. McIntyre, with whom Reid obtained many useful results for a few years.