A good way to prove to yourself that the appearance of a surface or shape differs from its reality, is to test it in some way.
The girl in the picture is measuring the appearance of a book. She has put two books on the desk, with their backs facing her. Under the cover of the top book she has placed a string long enough to allow her to hold both ends of it in one hand, in such a way as to hide the two ends of the cover. She knows that in reality the ends of the cover do not slant; they are perfectly horizontal. But she finds that to hide the ends of the cover she must bring the lines made by the string toward each other. This proves that the ends of the book in this position must be represented by slanting lines. When the strings hide the ends of the cover, she finds that they meet directly opposite the eye. Holding the string tight, and keeping their meeting point exactly opposite the eye, she slips a horizontal pencil between the two lines, starting near the place where they meet, and moving down until the pencil hides the further edge of the cover. The appearance of the cover is shown in the space bounded by the horizontal pencil, the nearer edge of the cover, and the two slanting parts of the string seen between them.
Arrange a large book on the desk in front of you. With a string, make the test that has been explained. Draw in values what you see.
The Study of Perspective.
What a Picture may Show Us. The pencil sketch on the next page would be quite difficult for you to draw, but it is not too difficult for you to understand and enjoy. It is one that will help you to use your eyes intelligently, in trying to find out of doors some of the things that are shown you in pictures. One of the best things that pictures can do for us is to help us to see in our own surroundings things that are interesting and beautiful.
Perspective. The lessons in this chapter have helped you to see how surfaces and shapes change in appearance, as they are seen under different conditions. You have also found that certain edges and outlines appear to change their direction, when seen in different positions. There is a name given to the study of these things, which you will often hear used. It is perspective. Perspective is only another name for the study of appearances, as differing from facts. You will hear some one say, for instance, that a certain sketch or picture is good in perspective; you will understand that the picture shows, in some interesting way, the effect of distance and position, or how certain appearances differ from actual facts.
Perspective of the Railroad. One of the best places in which to study perspective is on a bridge over a railroad track. You have noticed, no doubt, how the rails seem to come together as they stretch into the distance, and how the telegraph poles seem to grow shorter and shorter, until they disappear altogether. You know that the rails are just as far apart a mile away from you as they are at your feet, but a sketch drawn so would not be correct in perspective, because it would not show how the track looked.
Perspective Affecting Apparent Size. The sketch on [page 58] will interest you. Have you watched an engine grow from a mere speck in the distance to its full size as it rushes past you, and then grow smaller and smaller again as it hurries away, and finally disappears in the far-off horizon?
Perspective of a Street. Do you see anything on [page 64] that makes you think of the railroad? If you stand in the middle of the street and look down its length you will notice that the lines of the sidewalk seem to run together, that the trees and houses decrease in height as they are seen farther away, and that people in the distance appear smaller than people near you. When you can see these effects for yourself, you will begin to understand what the study of perspective means.