Although it is not safe to present simple statements in a field so complex as that of visual illusion where explanations are still controversial, it is perhaps possible to generalize as Jastrow did in the foregoing case as follows: If the direction of an angle is that of the line bisecting it and pointing toward the apex, the direction of the sides of an angle will apparently be deviated toward the direction of the angle. The deviation apparently is greater with obtuse than with acute angles, and when obtuse and acute angles are so placed in a figure as to give rise to opposite deviations, the greater angle will be the dominant influence. Although the illusion in such simple cases as Fig. 41 is slight, it is quite noticeable. The effect of the addition of many of these slight individual influences is obvious in accompanying figures of greater complexity. These individual effects can be so multiplied and combined that many illusory figures may be devised. In Fig. 42 the oblique lines are added to both horizontal lines in such a manner that _A_ is tilted downward at the angle and _B_ is tilted upward at the angle (the letters corresponding to similar lines in Fig. 41). In this manner they appear to be deviated considerably out of their true straight line. If the reader will draw a straight line nearly parallel to _D_ in Fig. 41 and to the right, he will find it helpful. This line should be drawn to appear to be a continuation of _C_ when the page is held so _D_ is approximately horizontal. This is a simple and effective means of testing the magnitude of the illusion, for it is measured by the degree of apparent deviation between _D_ and the line drawn adjacent to it, which the eye will tolerate. Another method of obtaining such a measurement is to begin with only the angle and to draw the apparent continuation of one of its lines with a space intervening. This deviation from the true continuation may then be readily determined. [Illustration: Fig. 42. The effect of two angles in tilting the horizontal lines.] [Illustration: Fig. 43. The effect of crossed lines upon their respective apparent directions.] A more complex case is found in Fig. 43 where the effect of an obtuse angle _ACD_ is to make the continuation of _AB_ apparently fall below _FG_ and the effect of the acute angle is the reverse. However, the net result is that due to the preponderance of the effect of the larger angle over that of the smaller. The line _EC_ adds nothing, for it merely introduces two angles which reinforce those above _AB_. The line _BC_ may be omitted or covered without appreciably affecting the illusion. [Illustration: Fig. 44.--Another step toward the Zöllner illusion.]