Perspective

is the principle by which an object recedin from the position of the viewer appears, to the viewer, smaller than its true size, and conversely, an object approaching the viewer's position seems more and more to approximate its true size. The knowledge of perspective is an indispensable aid to the artist, who must represent on a flat surface subjects which, in actuality, exist in three dimensionl space. As a test, take a ruler and measure a person forty feet away. As he approaches, see how much larger he seems to become. The test shows the apparent variation in size of an object, depending on its remoteness from or nearness to the viewer.
The vanishing point is that point on the horizon where parallel lines (perspective lines) seemingly converge and terminate. The vanishing point is always on the horizon. Any object within a picture will have perspective lines, though these lines are not visible in the finished drawing.
The horizon line is always on a level with the eyes of the observer, and it changes with the observer's changing positions, as shown in the drawings that follow.
The drawings in this book have been chosen to illustrate the variety of problems which the artist encounters when creating a picture. Study them carefully and then apply the principles which they present when next you make a sketch.

Perspective by Victor Perard - Pitman Publishing Corporation