James Arthur Bernard Horsley, electrical engineer, was the son of Stephen Horsley and his wife Marion Agnes, born Gibb. He was educated at Dover College, England, and served an apprenticeship at the Salford works of the General Electric Company. He came to the Witwatersrand in 1895 and during the next four years was responsible for one of the first three-phase installations in the gold mines. As a young man of 23 he served on the provisional committee, formed around the middle of 1897, to oversee the establishment of the South African Institute of Electrical Engineers. Once the Institute's constitution had been adopted in August that year a new management committee was elected, of which he was again a member. In June 1898 he read a paper before members of the Institute on "The amount of light required and the fittings suitable for the various operations of a gold mining company". He returned to the United Kingdom in 1899, after a serious illness.
Back in England Horsley joined the staff of the consulting engineer Robert Hammond and was involved in municipal and company electricity supply work until 1916. After serving in the navy until the end of World War I (1914-1918) he was appointed as HM Electrical Inspector of Mines, a post he held until his retirement in 1939. During these years he played a major role in the formulation of regulations for the safe use of electricity in mines and quarries. Among others he published three reviews of the latest developments relating to "Electricity in mines" in the Journal of the Institution of Electrical Engineers in 1928, 1931 and 1943. After his retirement he was employed for special duties by the Ministry of Fuel and Power until a few months before his death in 1952. During World War II he wrote a report for the Ministry, A review of electrical research and testing with regard to flame-proof enclosure and intrinsic safety of electrical apparatus and circuits... (London, 1944).
Horsley was elected an associate of the Institution of Electrical Engineers in 1895 and became a member in 1920. He was made an officer of the Order of the British Empire (OBE) in 1930. He was married to Mary Irene, born Valpy, with whom he had three children.