Optics principles. For example, the Ames room, Hering, Müller-Lyer, Orbison, Ponzo, Sander, and Wundt illusions all rely on the suggestion of the appearance of distance by using converging and diverging lines, in the same way that parallel light rays (or indeed any set of parallel lines) appear to converge at a vanishing point at infinity in two-dimensionally rendered images with artistic perspective. This suggestion is also responsible for the famous moon illusion where the moon, despite having essentially the same angular size, appears much larger near the horizon than it does at zenith. This illusion so confounded Ptolemy that he incorrectly
Tricritical point more components. It can be shown that three is the "minimum" number of components for which these points can appear. In this case, one may have a two-dimensional region of three-phase coexistence ("F" = 2-3+3 =2) (thus, each point in this region corresponds to a triple point). This region (F=2, P=3) will terminate in two critical lines of two-phase coexistence; these two critical lines (F=1, P=2) may then terminate at a single tricritical point. This point (F=0, P=1) is therefore "twice critical", since it belongs to two critical branches.<br> Indeed, its critical behavior is different from that of a conventional