Question: The inventor of the first thermionic valve made what visual mnemonic tool for generators?

Context paragraphs:
SY4307A: The EIA type 4307A is a power output pentode possessing a similar power rating, but significantly different characteristics to the far more common type 807 thermionic valve/vacuum tube.

John Ambrose Fleming: Sir John Ambrose Fleming FRS (29 November 1849 – 18 April 1945) was a British electrical engineer and physicist.  He is known for inventing the first thermionic valve or vacuum tube.  He is also famous for the left hand rule (for electric motors).  He was born the eldest of seven children of James Fleming DD (died 1879), a Congregational minister, and his wife, Mary Ann, at Lancaster, Lancashire and baptised on 11 February 1850.

Hugh McGregor Ross: Hugh McGregor Ross (31 August 1917 – 1 September 2014) was an early pioneer in the history of British computing.  He was employed by Ferranti from the mid-1960s, where he worked on the Pegasus thermionic valve computer.  He was involved in the standardization of ASCII and ISO 646 and worked closely with Bob Bemer.  ASCII was first known in Europe as the Bemer-Ross Code.  He was also one of the four main designers of ISO 6937, with Peter Fenwick, Bernard Marti and Loek Zeckendorf.  He was one of the principal architects of the Universal Character Set ISO/IEC 10646 when it was first conceived.

Royal Radar Establishment Automatic Computer: The Royal Radar Establishment Automatic Computer, or the RREAC, was an early solid-state computer in 1962.  It was made with transistors; many of Britain's previous experimental computers used the thermionic valve, also known as a vacuum tube.

Suppressor grid: A suppressor grid is a grid used in a thermionic valve (also called vacuum tube) to suppress secondary emission.  A suppressor grid is also called the antidynatron grid, as it helps to reduce the dynatron effect.

Fleming valve: The Fleming valve, also called the Fleming oscillation valve, was a vacuum tube (or "thermionic valve") invented in 1904 by John Ambrose Fleming as a detector for early radio receivers used in electromagnetic wireless telegraphy.  It was the first practical vacuum tube and the first thermionic diode, a vacuum tube whose purpose is to conduct current in one direction and block current flowing in the opposite direction.  The thermionic diode was later widely used as a rectifier — a device which converts alternating current (AC) into direct current (DC) — in the power supplies of a wide range of electronic devices, until beginning to be replaced by the selenium rectifier in the early 1930s and almost completely replaced by the semiconductor diode in the 1960s.  The Fleming valve was the forerunner of all vacuum tubes, which dominated electronics for 50 years.  The IEEE has described it as "one of the most important developments in the history of electronics", and it is on the List of IEEE Milestones for electrical engineering.

955 acorn triode: The type 955 triode "acorn tube" is a small triode thermionic valve (vacuum tube in USA) designed primarily to operate at high frequency; although data books specify an upper limit of 400–600 MHz, some circuits may obtain gain up to about 900 MHz.  Interelectrode capacitances and Miller capacitances are minimized by the small dimensions of the device and the widely separated pins.  The connecting pins are placed around the periphery of the bulb and project radially outward: this maintains short internal leads with low inductance, an important property allowing operation at high frequency.  The pins fit a special socket fabricated as a ceramic ring in which the valve itself occupies the central space.

Planetary mnemonic: A planetary mnemonic refers to a phrase used to remember the planets and dwarf planets of the Solar System, with the order of words corresponding to increasing sidereal periods of the bodies.  One simple visual mnemonic is to hold out both hands side-by-side with fingers spread and thumbs in the same direction, with the fingers of one hand representing the terrestrial planets, and the other hand the gas giants.  The first thumb represents the Sun and asteroid belt, including Ceres, and the second thumb represents the asteroid belt and trans-Neptunian objects, including Pluto.

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).  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.

Paraset: The Paraset was a small, low-power, thermionic valve CW morse code-only radio transmitter-receiver supplied to the resistance groups in France, Belgium and the Netherlands during World War II.

Supporting paragraphs: Fleming's left-hand rule for motors John Ambrose Fleming
Answer: Fleming's right-hand rule