The picket fence There was a fence with spaces you could look through if you wanted to. An architect who saw this thing stood there one summer evening. Took out the spaces with great care and built a castle in the air. The fence was utterly dumbfounded, each post stood there with nothing round it. Christian Morgenstern, The Art of Looking Sideways www.andrew.cmu.edu spacearchitectureabsurdity
Caustic (optics) Caustics made by the surface of water. In optics, a caustic is the envelope of light rays reflected or refracted by a curved surface or object, or the projection of that envelope of rays on another surface. The caustic is a curve or surface to which each of the light rays is tangent, defining a boundary of an envelope of rays as a curve of concentrated light. Wikipedia en.wikipedia.org Architectural CausticsCaustic Engineering caustics