John Michell

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John Michell (1724–1793) was an English clergyman and natural philosopher who explored astronomy, geology, optics, and gravity. Born in Eakring, Nottinghamshire, he studied at Queens’ College, Cambridge, where he later held various teaching and church posts. He spent his final years as the rector of St. Michael’s in Thornhill, near Leeds, and he died there in 1793.

Key ideas and achievements

- Dark stars and the, later, idea of black holes: In 1783–84 Michell proposed that a star could be so massive that light could not escape its gravity. He calculated that stars more than about 500 times the Sun’s size could trap light, making them invisible but detectable by the effects of their gravity on nearby objects. This was the first theory of what we would now call a black hole.

- Seismology and earthquakes: Michell suggested that earthquakes travel as waves through the Earth and he was the first to estimate the speed of these waves. He also designed a method to measure the Earth’s mass using a torsion balance, a device later used by Henry Cavendish to determine the gravitational constant.

- Magnetism and how magnets work: In 1750 he published A Treatise of Artificial Magnets, describing how to make strong magnets and explaining how magnetic forces follow an inverse-square law. His work laid important groundwork for the science of magnetism.

- Astronomy and statistics: Michell was the first to apply statistics to the study of the stars. He showed that binary stars and star clusters occur far more often than random chance would predict, providing early evidence of gravitational interactions in the heavens.

- Geology and the Earth’s crust: After the 1755 Lisbon earthquake, he wrote about how earthquakes illuminate the Earth’s crust and its layers. He argued that the Earth has a regular, layered structure and helped advance what we now call stratigraphy, including early ideas about the Mesozoic era in Britain.

- Influence and recognition: Michell was elected to the Royal Society in 1760 and served as Woodwardian Professor of Geology at Cambridge for a time. He built telescopes and corresponded with leading scientists of his day, including William Herschel. His ideas about gravity, light, and the Earth’s interior were ahead of his time and often praised only long after his death.

Personal life

Michell’s first wife was Sarah Williamson; she died a year after their marriage. He later married Ann Brecknock, with whom he had a daughter, Mary. He was known as a capable experimenter and instrument maker, and he is remembered as one of the greatest yet most overlooked scientists of the 18th century.