Abstract
In the first experiment the apparent lengths of the minor diagonals and major diagonals of two parallelograms of the Sander figure were measured. The minor diagonals were overestimated and the major diagonals were underestimated. According to the law of good gestalt, a distorted form has a tendency to be restored to the good form, and the illusion is caused by this restoration tendency. If so, it may be hypothesized that the more distorted a figure is, the greater the illusion magnitude is. In the second experiment various distorted parallelograms were constructed, and the apparent lengths of the minor or major diagonals of those various parallelograms were measured. It was found that the greatest overestimation of the minor diagonal and the greatest underestimation of the major diagonal occur in the most distorted parallelograms irrespective of the relative sizes of the areas of the parallelograms.
