Inventor of the percussion cap. Born Belhelvie (Aberdeenshire), the son of a Presbyterian minister, he took over his father's parish in 1790. Fond of game shooting, he realised the major problem with the flint-lock gun was its unreliability in damp conditions. By 1805 he has designed a new priming system, which he patented in 1807. A percussion cap ignited an enclosed charge when struck by a hammer. At first enthusiastically received by the army, who gave him a workshop in the Tower of London, support was later withdrawn. Undaunted, he continued to develop his system and even rejected an offer of £20,000 for his invention from Napoleon. This was later developed into the modern bullet.
He is remembered by a memorial in the Tower of London (1929), a replica of which was erected in 1931 on the Cromwell Tower, where he conducted experiments, at King's College (Aberdeen).