ABSTRACT

As the effect of this optical illusion entirely depends on correctly placing the sight piece, a piece of card for that purpose must be cut out of the exact sixe and shape of the figure A. B. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003101543/baf1193d-4bfb-45b8-ac46-0a7613b6dbbf/content/figu_65_OB.jpg"/>