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John HadleyEnglish mathematician
Date of Birth: 16.04.1682
Country:  Great Britain |
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Biography of John Hadley
John Hadley, an English mathematician, was born on April 16, 1682, in Bloomsbury, London. His parents were Katherine FitzJames and George Hadley. His younger brother, George, became a renowned meteorologist. In 1717, John was appointed as a fellow of the Royal Society of London, later becoming its vice-president.
Inventor of the Octant
Hadley gained the most recognition for inventing the octant, a precursor to the sextant, around 1730. The octant was used for measuring the altitude of the sun or other celestial objects above the horizon at sea. His invention proved extremely valuable for navigation and replaced instruments such as Davis quadrant. Thomas Godfrey independently invented the octant around the same time as Hadley.
Contributions to Astronomy
Besides his work on the octant, Hadley was also known for developing aspherical and parabolic lenses used in reflector telescopes. In 1721, he demonstrated the first Newtonian telescope to the Royal Society. His design utilized a 150mm diameter lens, making his telescope much more compact than the giant air telescopes of his time. Despite the mirror being slightly smaller than Huygens' eyepiece, Hadley's telescope was only 1.8m in length. He also crafted Gregorian telescopes with flawlessly shaped mirrors and very low spherical aberration.
Legacy and Personal Life
When Hadley's name gained recognition, he formulated the fundamental principles that aided other astronomers in determining the appropriate size of mirrors for their telescopes. He did not document his technique for grinding and polishing mirrors, but he passed on his knowledge to other specialists through oral transmission. On June 6, 1734, Hadley married Elizabeth Hodges, a financially independent woman. They had one child, a son named John, born in 1738.
John Hadley passed away at the age of 62 on February 14, 1744, in East Barnet, Hertfordshire. The lunar mountains, Mons Hadley and Rima Hadley, were named in his honor. Additionally, the Oasis Academy Hadley in Enfield was named after him.
