This chapter describes a set of discoveries made by us or by others which also led up to ecological optics. It presents a glossary of terms or definitions that are more or less in use in ecological optics and that set of definitions will unquestionably provide grounds for argument for the rest of the week. A second discovery that led up to ecological optics came from an experiment done in Morrill Hall with a device called the optical pseudotunnel. In W. Metzger’s experiment with the plaster wall which was looked at by an observer, if students turned the illumination up high he could see the surface at a fixed distance and in a specific color and at a specific slant, and only then could he see the surface. Wolfgang Metzger and K. Koffka applied the word “texture” or “microstructure” to both the light and the substance.