What Is Perspective?
Perspective is the science which furnishes us with the laws by which we can give the apparent, as geometry those by which we can give the real, forms of objects. These laws are obvious without rules to thoughtful, artistic common-sense—but, to many, books on the subject will always be useful, if not indispensable. The science was called perspective, or seeing through, from an impression that the correct foreshortening of objects could be gained by viewing and tracing them through a pane of glass. This plan only ensures correctness when the plane of the eye is parallel to that of the medium upon which the drawing is made. A picture in perspective is simply a plane parallel to the plane of the eye intersecting the rays that come from the surface of the objects represented. The points of these rays at the places of their several intersections combine to form the true perspective representation. This was the art that Mantegna made so much of at Padua; and that with which Bellini, the painter of the National Gallery “Doge,” delighted the Venetians. Without much semi-scientific pedantry, the whole science may be understood by balancing a half-crown on the top of the forefinger of your right hand. Hold it up so that its broad plane is parallel to the eye’s plane; put it nearer or further, and it seems to increase or diminish in size. Turn it obliquely, and it appears an oval; put the edge on a line with the eye, and it appears a mere thin straight line. A sphere is the only geometric form that undergoes no perspective changes. The eye is able to take in any given space set at an angle of under sixty degrees. When both eyes view a scene, instead of the circle one eye sees, we have an ellipse formed by the continuation of the two circles of vision,—the point of sight being opposite the centre of the space between the two eyes. Perspective is of great use in Art; but the books upon it are too abstruse, and imply a knowledge of mathematics. [This common-sense explanation is from the pen of Professor Wallace, M.A., in the first number of a journal edited by him and entitled The Public Instructor.]