Geometrical forms of Abelès'' equations involving film thickness

Abelès' equations (in terms of ₁; ₂ and optical film thickness x) for all the eight optical functions (R_s; R_p; T_s; T_p; F_s; F_p; X_s and X_p) have been expressed in the form of equations representing standard geometrical three-dimensional figures. X_s and X_p are represented by plane surfaces whilst the remainder are skew cones. Translated into the n; k notation; X_s and X_p generate hyperboloids whilst the remainder produce paraboloids whose cross-sections are parts of figures of eight.