John Hadley facts for kids
Quick facts for kids
John Hadley
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| Born | 16 April 1682 |
| Died | 14 February 1744 (aged 61) East Barnet, Hertfordshire
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| Nationality | English |
| Known for | Octant |
John Hadley (born April 16, 1682 – died February 14, 1744) was an English mathematician. He is famous for inventing the octant. This important tool helped sailors find their way at sea. Another inventor, Thomas Godfrey, also claimed to have invented it around the same time.
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About John Hadley
John Hadley was born in Bloomsbury, London. He was the oldest son of George Hadley and Katherine FitzJames. His younger brother, George Hadley, became a well-known scientist who studied weather.
In 1717, John Hadley became a member of the Royal Society of London. This is a very old and respected group for scientists. He later became a vice-president of the society. He passed away in 1744 in East Barnet. He is buried there with his family.
Hadley's Inventions
John Hadley created several important tools. His inventions helped people explore and understand the world better.
The Octant
In 1730, Hadley invented the reflecting octant. This device was very useful for sailors. It helped them measure the height of the sun or stars above the horizon. By knowing this height and the time, sailors could figure out their exact location at sea.
The octant worked by using mirrors. One mirror moved along a curved scale. This allowed the user to see a reflected image of a star or the sun. This image would line up with the horizon, which was viewed directly. The octant was much better than older tools like the Davis quadrant. It became a key tool for navigation.
Better Telescopes
Hadley also worked on improving reflecting telescopes. These telescopes use mirrors to gather light. In 1721, he showed the Royal Society of London a new type of telescope. It was a Newtonian telescope with a special curved mirror. This mirror was shaped like a parabola.
His telescope had a 6-inch (150 mm) main mirror. It worked as well as the very large, long telescopes of his time. He also made Gregorian telescopes with accurately shaped mirrors. These improvements made telescopes more powerful and easier to use.
Honors and Legacy
John Hadley's work was very important. He is remembered for his contributions to science.
- Two places on the Moon are named after him: Mons Hadley (a mountain) and Rima Hadley (a valley).
- A school in north London, Oasis Academy Hadley, is also named in his honor.
See also
- List of largest optical telescopes in the 18th century
