Alexander P. Trotter, consulting engineer, was educated in the natural sciences at Trinity College, Cambridge, and completed an apprenticeship with the engineering firm Easton and Anderson at Erith, just east of London. During 1881-1883 he took out patents for prismatic glassware. From 1883 to 1887 he was a partner in the firm Goolden and Trotter, one of the early dynamo manufacturers, in Halifax, Yorkshire. In 1890 he became editor of the journal The Electrician, serving in this position to 1895. He was married to Alys F. Keatinge, an artist, writer and authority on Cape Dutch architecture, with whom he had one son and one daughter.
In December 1895 Trotter was appointed to the newly created post of Government Electrician and Inspector under the Electric Lighting and Power Act of 1895 at the Cape of Good Hope, arriving to assume duty in February 1896. He established a Government Electrical Laboratory that same year to test electrical meters, insulation, standard cells, etc, initially in a room at the South African College. One of the problems he investigated during 1896 was interference in the west coast submarine telegraph cable, caused by Cape Town's electric tramways. The problem was eventually solved by laying a special section of cable to carry the return current out to sea. An account of the work, "Disturbance of submarine cable working by electric tramways", was published in the Journal of the Institute of Electrical Engineers (1898).
The laboratory was moved to a room in the General Post Office during 1897. That year Trotter made comparative tests of the illuminating power of different brands of paraffin oil. In 1898 his post was renamed Government Electrical Engineer. He returned to England in 1899 and was succeeded by G.M. Clark*. During his stay he was a member of the South African Philosophical Society, serving on its council for a year from September 1896, and was an examiner in physics for the University of the Cape of Good Hope.
Trotter returned to England via the east coast of Africa and from Cape Town to Durban travelled on the same ship as R.T.A. Innes*. During this part of the voyage they observed so-called anti-solar rays (sunbeams converging on a point in the sky directly opposite the setting sun). Many years later Trotter publihsed a brief account of these observations, and their explanation in terms of perspective, in Nature (1938, Vol. 141, p. 558). Upon his arrival in England Trotter became electrical adviser to the Board of Trade (1899-1917). He was a member of the Institution of Civil Engineers, the Institute of Electrical Engineers, and the British Association for the Advancement of Science (from 1884); a Fellow of the Physical Society; and at some time was president of the Illuminating Engineering Society. He published many papers from 1884 onwards, as well as some books, including Illumination: its distribution and measurement (1911) and The elements of illuminating engineering (1929).