pastel artist, amateur astronomer, and literary scholar, whose brilliantly coloured chalk portraits were highly appreciated in 18th-century England. His works were considered on a par with those of Sir Joshua Reynolds (Reynolds, Sir Joshua).

An evangelical Methodist, he often voiced his religious views while drawing those who posed for him. He was retained as painter to George III. He also wrote several aesthetic and technical treatises on literature and painting. For 50 years he kept a diary on his religious exercises, and he laboured for 20 years with telescope and engraving tools on a lunar map.