116. The use of arches should be studied. A space that is arched looks wider than it actually is, for the eye unconsciously follows the lines of the arch, and a distance or width effect is the result. The same space treated with a straight line is quickly bridged. The same space treated with lines that come to an angle looks narrower, for the reason that the eye becomes focused by the apex of the angle, and a height effect, not a breadth effect, is the result. (See page [57].)
117. This illusion is best shown in the illustrations of the parallel lines that are crossed diagonally, with the result that the lines no longer look parallel because of the angles. Nevertheless, they are parallel, and the lines running diagonally at the bottom of this page are also parallel.
We present two practical illustrations of illusion in the use of lines. (See [¶ 112].) They represent the side-walls of two rooms of the same dimensions, but showing apparently different proportions, the perpendicular lines making the side-wall look higher and the horizontal lines making the side-wall look lower. (See page [59].)
Illustration A.
