of perspective with perspective as a whole. There are as many systems of perspective as there are conventional laws for the representation of space.
The practice of drawing and painting offers the student the following problem in descriptive geometry: to represent the three dimensions of space by means of a plane surface of two dimensions. The Egyptians and Assyrians solved this problem by throwing down vertical objects upon one plane, which demands a great effort of abstraction on the part of the observer. European perspective, built up in the fifteenth century upon the remains of the geometric knowledge of the Greeks, is based on the monocular theory used by the latter. In this system, it is assumed that the picture is viewed with the eye fixed on a single point. Therefore the conditions of foreshortening--or distorting the actual dimensions according to the angle from which they are seen--are governed by placing in harmony the distance of the eye from the scheme of the picture, the height