Used with
permission of Maiken Naylor, University at Buffalo, Buffalo, NY, USA,
http://ublib.buffalo.edu/libraries/units/sel/exhibits/stamps
August Ferdinand Moebius (1790-1868), another astronomer and mathematician, was one of the founders of topology. His Moebius strip is a strip whose ends are joined after giving it a half twist; it has only one side and one edge, and here promotes a mathematical congress in Brazil.