The son of a High Sheriff of Hertfordshire, I am recognized as one of the premier craftsmen of mathematical instrucments.
Though I never gained a formal education at a university, people claim that I somehow knew more advanced mathematics than "was usual."
My first success was the creation of new grinding techniques to produce a large reflecting telescope of great quality (f/12 and aperture 6 inches, if that means anything to you) that was used by astronomers James Bradley and Edmond Halley.
In 1730 I created a reflecting quadrant, which eventually evolved in the modern sextant; though this creation led to priority fights with Newton and Hooke, my design won out because it was portable and adopted by navigators.
In 1732, I adapted a quadrant to include a "bubble-level" that allowed its use by navigators at sea even when the horizon was not visible.
I devised a way to test parabolic mirrors by placing a tiny illuminated pinhole at the mirror's center of curvature and then examining the reflected cone of light in the vicinity of the image.
You can now see many of my mathematical instruments on display in the Science Museum in London.
John Hadley (1682 - 1744)