When Do Two Figures Seem Equal in Size?

Figures with an equal surface area give an unequal size impression, e.g., in Fig. 1 it seems that c is bigger than b, although their surface areas are alike. W e hypothesized that the size impression of a figure not only depends on its physical size (its surface area) but also on the length of irs contour. More precisely, we suppose that two figures seem alike in size if their surfaces are inversely proportional to their dispersions [dispersion = (contour)~surface] , e.g., in Fig. 1 it seems that a = b.