English jurist and mathematician who invented the achromatic lens, which he utilized in building the first refracting telescope free from chromatic aberration (colour distortion).

Convinced from study of the human eye that achromatic lenses were feasible, Hall experimented with different kinds of glass until he found (1729) a combination of crown glass and flint glass that met his requirements. In 1733 he built several telescopes with apertures of 2.5 inches (6.5 cm) and focal lengths of 20 inches (50 cm).

John Dollond of London received the Copley Medal of the Royal Society in 1758 for the invention, but his right was contested by yet another inventor in 1766. It was Hall, however, who was established as the originator of the achromatic lens, although he was largely indifferent to priority claims.