No. LXXII.—HEXAGONAL ILLUSIONS
If we look with one eye only, or with eyes half-closed, at these groups of circular dots, they assume the appearance familiar to us in honeycomb. This is an effect of the contrast and opposition of the black and white in the sensation of the retina.
Although the black and the white circles are of the same diameter the irradiation is in their case so intense that the white circles appear to be larger than the black.