Born Feb. 14, 1858, in Penpont, Dumfriesshire; died Aug. 2,1895, in London. British geologist and explorer of Africa.
In 1879 and 1880, Thomson made his way from Zanzibar to the northern end of Lake Nyasa and explored the territory, previously unknown to Europeans, between Lakes Nyasa and Tanganyika; he also followed the Lukuga River for some distance from its source in Lake Tanganyika and discovered Lake Rukwa. In 1881, Thomson explored the Ruvuma River. While traversing the territory between Mombasa and Lake Victoria in 1882, he explored the interior of what is now Kenya, where he discovered Lake Baringo and the volcanic massif Mount Elgon.