To produce the illusion: Take an ordinary water glass, put a little water in it, stretch some plastic wrap tightly over the glass and put it in the microwave for a few seconds.
Leave it in the microwave for a minute to cool down .(Please don't do anything stupid and scald yourself.) Remove the glass (see above, "....stupid") from the microwave. The plastic should have formed a concave beaded surface on the top of the= glass. Wonder, "What is the mathematical form of that surface?" Examine the surface under a vertical lamp (like a desk lamp or a ceiling bulb) An image of the lamp willl appear floating inches above the surface of the plastic. Tilt the glass just right, and you will see a *convex* surface enclosing the top of the glass. Wonder: "Have I made a parabolic surface?" Write email to Friam. Receive dope slaps from colleagues for not looking it up on the internet first. -- Nicholas S. Thompson Emeritus Professor of Psychology and Ethology Clark University [email protected] https://wordpress.clarku.edu/nthompson
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