Fig. 24.—A striking illusion of perspective.
The effect of contrast is seen in a in [Fig. 23]; that is, the short parallel lines appear further apart than the pair of long ones. By adding the oblique lines at the ends of the lower pair in b, these parallel lines now appear further apart than the horizontal parallel lines of the small rectangle.
The influence of perspective is particularly apparent in [Fig. 24], where natural perspective lines are drawn to suggest a scene. The square columns are of the same size but the further one, for example, being apparently the most distant and of the same physical dimensions, actually appears much larger. Here is a case where experience, allowing for a diminution of size with increasing distance, actually causes the column on the right to appear larger than it really is. The artist will find this illusion even more striking if he draws three human figures of the same size but similarly disposed in respect to perspective lines. Apparently converging lines influence these equal figures in proportion as they suggest perspective.
Fig. 25.—Distortion of a square due to superposed lines.
Although they are not necessarily illusions of perspective, [Figs. 25] and [26] are presented here because they involve similar influences. In [Fig. 25] the hollow square is superposed upon groups of oblique lines so arranged as to apparently distort the square. In [Fig. 26] distortions of the circumference of a circle are obtained in a similar manner.