Physiognomy is the art of interpreting a person’s psyche from his outward appearance. Today physiognomy is dismissed as unscientific, but in the 18^th century, the Finnish-Swedish mathematician A. J. Lexell put the method to a serious test. On his European journey in 1780–1781, he met with the famous mathematicians and philosophers of his time and used his skill to interpret their spiritual condition. The results were not convincing, but Lexell’s vivid descriptions of his contemporaries remain an important eye-witness to the Enlightenment.