British optician (optics) who, though lacking a theoretical background, invented the triple achromatic lens still in wide use, made substantial improvements in the astronomical refracting telescope, and improved navigation instruments of his day. In 1765 he combined two convex lenses of crown glass with one double-concave lens of flint glass to make a triple achromatic lens that rendered images free from extraneous colour and greatly reduced the spherical error of existing equipment.