Perspective

PERSPECTIVE, deals with the phenomena of appearance; usually applied to the construction of drawings intended to repre sent objects as seen from some definite point of view. In appear ance an object may seem very unlike what it is known to be in reality. A railway track is of the same width throughout its length, yet in appearance the rails seem to approach one another as they recede, Plate I., fig. 2. A cube is known to have 12 edges all equal in length and to have a perfect square for each face, but when viewed the edges do not appear to be equal, nor do the faces appear to be squares, Plate I., fig. 6.

Isometric

Drawing.—A method of representing objects is sometimes used in which dimensions in three directions are shown in their true size to the scale of the drawing. A cube con structed by this method is given in fig. 1. Every line in the direction of ab, of ac, or of ae, is drawn at its true scale. Thus all the edges of the cube as shown are of equal length. Such a drawing is known as an isometric. It is useful in indicating the size of an object, as three dimensions at right-angles to one another can be shown upon a single plane surface. It is a purely arbitrary method of representation, how ever, gives a distorted picture of the ob ject, makes no pretence of reproducing its appearance, and should never be confused with true perspective.

True Perspective.

In true perspective three lines at right angles to one another cannot all appear in their true lengths. Lines and forms seem to change in size and shape as they occupy differ ent positions in the picture. Colours and lightings seem to change as well. In the foreground objects appear brilliant with distinct details, clear colours, dark shadows and strong contrasts. As one looks farther into the distance objects seem less brilliant, con trasts less marked, colours gradually lose their clearness and tend to merge into a purplish monotone. This is caused in part by minute specks of dust or moisture held in the atmosphere which reflect a soft hazy light into the picture. These lighting effects are outside the scope of the present article. The apparent changes in

form, however, are dealt with as an exact science known as linear perspective, by means of which it is possible to construct, from the actual dimensions of an object, its apparent shape and size at any point in space.

The camera is an instrument by means of which perspective views can be produced mechanically. On Plate I., figs. 2 and 6 are so produced. Rays of light reflected from any object, as ab, fig. 2, pass through the lens of the camera and fall upon the sensitive plate forming an image which will represent the appear ance of the object to one who views the photograph.

The human eye, fig. 3, is, in effect, a little camera with a lens, o, and a sensitive surface, the retina, which receives the image, fe. If a transparent plane, PP, be placed between the object and the observer's eye, the rays of light coming from the object will pass through the plane and pro ject upon it an image, cd, of the object. The image on the plane would be a perspective of the object and would represent to the observer its appearance.

Wherever one looks he sees a perspective view. An expert draftsman before a group of objects might record on paper exactly what he saw. The result would be a perspective drawing reproducing the appearance of the objects and might conceivably be made without any understanding of the laws of perspective. Some of the ancient peoples, the Chinese for example, developed an interesting technique in drawing, and their pictures often showed a strong sense of perspective. Whether they understood the under lying science or merely copied what they saw is open to argu ment. It was probably not until the early part of the r5th cen tury that the governing principles of the science began to be understood by western civiliza tion. The names of Brunelleschi, Alberti, Ucello, Leonardo da Vinci, Piero della Francesca and Albrecht Diirer are all connected with its development. To Fran cesca has been attributed the conception of the vanishing point which is the key to modern perspective construction.