“The circle . . . is the synthesis of the greatest oppositions. [It] combines the concentric and the excentric in a single form, and in equilibrium. Of the three primary forms [triangle, square, circle], it points most clearly to the fourth dimension.”
(Vasily Kandinsky to Will Grohmann, October 12, 1930, quoted in Angelica Zander Rudenstine, The Guggenheim Museum: Paintings 1880–1945, vol. 1 [New York: Solomon R. Guggenheim Foundation, 1976], p. 310.)