II.
Linear Perspective
General remarks on perspective (40—41).—The elements of perspective:—of the point (42—46).—Of the line (47—48).—The nature of the outline (49).—Definition of perspective (50).—The perception of the object depends on the direction of the eye (51).—Experimental proof of the existence of the pyramid of sight (52—55).—The relations of the distance point to the vanishing point (55—56).—How to measure the pyramid of vision (57).—The production of the pyramid of vision (58—64).—Proof by experiment (65—66).—General conclusions (67).—That the contrary is impossible (68).—A parallel case (69).—The function of the eye, as explained by the camera obscura (70—71).—The practice of perspective (72—73).—Refraction of the rays falling upon the eye (74—75).—The inversion of the images (76).—The intersection of the rays (77—82).—Demonstration of perspective by means of a vertical glass plane (83—85.)—The angle of sight varies with the distance (86—88).—Opposite pyramids in juxtaposition (89).—On simple and complex perspective (90).—The proper distance of objects from the eye (91—92).—The relative size of objects with regard to their distance from the eye (93—98).—The apparent size of objects denned by calculation (99—106).—On natural perspective (107—109).