John Ambrose Fleming (1849-1945)

Sir John Ambrose Fleming was an electrical engineer and physicist best known for inventing the thermionic valve and for his work on wireless communication. He was born in Lancaster to a Congregational minister, the eldest of seven children, and grew up in north London as a devout Christian with aspirations of becoming an engineer. Already at the age of 11 he was building model engines and boats in his own workshop. As his training was beyond his family’s means he gradually financed his own education by alternating study with paid work. He gained his first degree at University College London in 1870, and followed it with further study including a first-class doctorate degree in chemistry and physics at St John’s College, Cambridge, completed in 1879.

He was appointed the first Professor of Physics and Mathematics at the University of Nottingham, but left soon after in 1882 to become a consultant electrician to the Edison Electrical Light Company, before returning to University College London as a member of staff in 1885, where he remained as a lecturer until his retirement in 1927. He was the first head of the first university department of electrical technology in England.

Fleming participated in experiments by Marconi with wireless communication, including the 1899 communication across the English Channel, and in 1900 he helped Marconi design the first electric wave power station to wirelessly transmit signals from Cornwall across the Atlantic. In 1904, Fleming invented the thermionic valve, known as the Fleming valve, which could convert electrical oscillations into continuous current. This was the first electron tube device, and it would pave the way for the modern electronics industry, remaining dominant until transistors emerged in the 1970s. Versions of the original valve are still used today in some transmitters and amplifiers. He additionally developed a wave meter called a cymometer, which could read resonance and wavelength on a calibrated scale.

Fleming published many books over his career. He was awarded the Faraday Medal of the British Institution of Engineers in 1928, was knighted in 1929, and received the IRE Medal of Honour in 1933 for his contribution towards engineering principles in radio. At the centenary celebration of the thermionic valve’s invention, it was described as ‘the device that gave birth to modern electronics’, enabling the detection of radio waves and greatly contributing to the ‘wireless revolution’.