Engraving with Ayrton's signature. Ayrton (1847-1908) studied under Lord Kelvin at Glasgow. In 1873 he was appointed to the first chair in natural philosophy and telegraphy at Imperial Engineering College, Tokyo. In 1879 he was the first to advocate power transmision at high voltage, and with John Perry (1850-1920) he invented the spiral-spring ammeter, the wattmeter, and other electrical measuring instruments. The ammeter (a contraction of ampere meter) was one of the first to measure current and voltage reliably. They also worked on railway electrification, produced a dynamometer and the first electric tricycle. Ayrton worked on the electric searchlight with his second wife Phoebe Marks (1854-1923), later famous for her work on the electric arc.
© Science Museum / Science & Society Picture Library