For those readers who shared my frustration at not being able to conduct the sugar experiment referred to in Richard Feynman's "Surely You Must Be Joking, Mr. Feynman" (Book Review, Feb. 24), a number of helpful closet sugar-crackers, including the senior research fellow at Hughes Labs, both called and wrote me to explain: "Please don't disbelieve Prof. Feynman about the luminescence of sugar crystals (it was even documented in Science American not too long ago). Hint: Wint-o-Green Lifesavers (preferably more than one in the mouth at a time) chewed in front of a mirror in a darkened room. Immense fun--a faithful Book Review reader." The senior fellow warned that, "unless your crowns are in good condition," you might insist on having children do the actual chomping for you. Also, wait long enough for your eyes to adjust to the darkness.