Educated at St Thomas's Hospital, where his career was brilliant, for he won the Tite Scholarship in 1877 and took successively the Musgrove Scholarship in 1878 and 1879, the Grainger Testimonial Prize in Anatomy and Physiology in 1879, the Cheselden and Treasurer's Gold Medals and the Solly Medal and Prize. He was Prosector of the Royal College of Surgeons, and was awarded a first-class Certificate of Honour. He was appointed Resident Accoucheur at St Thomas's Hospital, and very shortly afterwards was elected Assistant Obstetric Physician and Lecturer on Obstetric Medicine at the Middlesex Hospital Medical School, with which he henceforth completely identified himself. In 1889 he became full Obstetric Physician, and held this position till 1908, when he was elected Consulting Physician. He was also at one time Consulting Physician to the Chelsea Hospital for Women and Senior Physician to the Royal Hospital for Children and Women, and in 1909 was appointed an Examiner in Midwifery and Diseases of Women for the Conjoint Board, and was also Examiner in Obstetric Medicine at the Victoria University, Manchester, the University of Glasgow, and the Society of Apothecaries of London. He was a Vice-President of the Obstetrical Society. Duncan is described as a good operator, particularly gentle in handling tissues. His results were good, in spite of the fact that he did not fully adopt the modern aseptic technique. Had his entire energies been applied to his professional work he would have accomplished far more than he did, but his conviction that national defence was the first concern of all men led him to devote much of his time to voluntary military service. He was awarded the Territorial Decoration in 1909, and for the following five years served as Lieutenant-Colonel Commanding the Middlesex Hussar Yeomanry. Comparatively late in life he was made a freemason, but worked with such enthusiasm at the craft as to become a Grand Officer in 1907. He was a Founder of the Middlesex Hospital Lodge and the Middlesex Yeomanry Chapter. Duncan was devoted to the country life. He lived at Shenley for some years before and after his retirement, and was popular with villagers and farmers alike. He died at his residence in Oakwood Court, Kensington, on October 18th, 1917. Publications:- "Report of the Obstetrical Department of St Thomas's Hospital for 1881-82-83." - *St Thomas's Hosp. Rep.*, xii, xiii. *On the Commoner Accidents attending Parturition, their Immediate and Remote Effects; with Treatment*, 8vo, London, 1886. "On the Extirpation of the Entire Uterus," 8vo, 8 charts, London, 1880; reprinted from *Trans. Obst. Soc. Lond.*, 1885, xxvii, 893. *Clinical Lecture on Extra-uterine Gestation*, 8vo, London, 1890. "A New Treatment for the Vomiting of Pregnancy." - *Lancet*, 1887, ii, 754. "On Chronic Disease of the Uterine Appendages. With a Table containing Short Notes of Thirty Consecutive Cases treated by Abdominal Section," 8vo, illustrated, London, 1891; reprinted from *Trans. Med. Soc.*, xiv, 214.