The inventor of the first thermionic valve made what visual mnemonic tool for generators?
Fleming's left-hand rule for motors: Fleming's left-hand rule for motors is one of a pair of visual mnemonics, the other being Fleming's right-hand rule (for generators). Fleming's left-hand rule for motors:  They were postulated by John Ambrose Fleming, in the late 19th century, as a simple way of working out the direction of motion in an electric motor, or the direction of electric current in an electric generator. John Ambrose Fleming: Sir John Ambrose Fleming FRS (29 November 1849 – 18 April 1945) was a British electrical engineer and physicist. John Ambrose Fleming:  He is known for inventing the first thermionic valve or vacuum tube.
Fleming's right-hand rule