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Brightening Ideas

On April 16, 1682, English mathematician and instrument maker John Hadley was born.

He developed precision mirrors to improve the accuracy and power of the reflecting telescope. Until Hadley, telescopes used mirrors that were spherical in shape. These were often blurry and/or distorted the image in small ways. Hadley created mirrors that were parabolic in shape. He was the first to develop both techniques and method for producing mirrors with very little image distortion.

With its ability to capture better light and produce a sharper image, Hadley was able to enclose the works into a short tube that had two brilliant advantages – it kept out unwanted light from sources nearby and it was portable.

Because he published his methods of polishing and parabolization and instructed others how to do so, Hadley influenced not only the field of optics but helped popularize reflective telescopy.

Always eager to tackle interesting problems, Hadley was motivated to accept another investigation. After a naval fleet had shipwrecked at sea, England’s Parliament offered a huge money award for any method to find longitude at sea to within one degree. Hadley took on the challenge!

Hadley used his skills to invent the octant for navigation that measured the altitude of the Sun or a star above the horizon to determine geographic position at sea. The precursor of the sextant, this instrument was widely used for its accuracy and ease of use and provided a sound base for future innovation.

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