A state of quietness Tea is said to be the way. This is because it is something one learns to appreciate through feeling, not through verbal instructions. If a person maintains a state of quietness, only then will one appreciate the quietness inherent in tea. Lu Yu, The Book of Tea silenceunderstanding
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