As for everything else, so for a mathematical theory: beauty can be perceived but not explained.

Quoted in J R Newman,

Projective geometry is all geometry.

Quoted in J R Newman, *The World of Mathematics* (New York 1956).

Not that the propositions of geometry are only approximately true, but that they remain absolutely true in regard to that Euclidean space which has been so long regarded as being the physical space of our experience.