The spectacular optical illusion of the hollow mask is considerably improved by filling the mask with a transparent medium. The mask seems to stare more directly at the onlooker and its deceptive motions follow his movements over a wider field. The history of the illusion of the hollow mask is outlined and the legend of the Bust of the Tyrant is invented. Other ways of making a bust which follows the moving onlooker face to face are discussed.
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