南回归线
In discussing the habitability of lands under the Torrid Zone and Tropic of Capricorn, D'Ailly drew on the "Opus Majus", written around the year 1267 English monk and scholar Roger Bacon. With regard to the "Regio Patalis," Bacon said: “the southern frontier of India reaches the Tropic of Capricorn near the Region of Patale and the neighbouring lands which are washed by a great arm of the sea flowing from the Ocean”. Patala was on or just south of the Tropic of Cancer, not south of the Equator, but somehow Roger Bacon had confused the Tropic of Capricorn with the Tropic of Cancer under which, on the day of the summer solstice, shadows at Patala were cast southward.