His work with James Bradley attempting to measure stellar parallax led to the discovery of the aberration of light.

Molyneux is best known for his work with Bradley in attempting to measure the parallax of Gamma Draconis leading to the discovery of the aberration of light.

Like Hooke, Molyneux decided to take advantage of Gamma Draconis being a star that passes directly overhead in London, minimizing the effects of atmospheric refraction on its apparent position when it does so.

Molyneux commissioned a larger set of telescopes and employed James Bradley as an expert who had more astronomical and mathematical knowledge.

He was treated by court anatomist Nathaniel St André, but the treatment did not prove successful, and Molyneux died in Kew in April.