Ubiratan D’Ambrósio, an authority on the fields of ethnomathematics, math education and the history of mathematics, offers two talks at Bates College on Sept. 18. D’Ambrosio offers an informal look at 19th-century Brazilian mathematician Joaquim Gomes de Souza at 4:30 p.m. His second talk, Bates' annual Sampson Lecture, is titled "Ethnomathematics in a Global World" and begins at 7:30 p.m.