 He succeeded in explaining the colour of thin and of thick plates (diffraction), and the inflexion of light, and he wrote on double refraction, light polarisation and binocular vision.He also invented a reflecting quadrant for observing the angles between the moon and the fixed stars— the same in every essential as the historically important navigational instrument more commonly known as Hadley's quadrant.This discovery was communicated by him to Edmund Halley in 1700 but was not published, or communicated to the Royal Society, until after Newton's death, when a description of it was found among his papers.