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A TASTE OF CROW, PART ONE

Re the 10-inch post-sushi stomach worm [August 11], enclosed is a page from a recent Nutrition Action Healthletter. Turns out the Sushi Worm From Hell was "only" about 1 1/2 inches long. Some comfort. --Junu Kim, Chicago

It seems the editors of Nutrition Action, from which I got this horrifying item, multiplied instead of dividing when converting from the metric. I am surrounded by schmucks.

A TASTE OF CROW, PART TWO

Your discussion of hair [July 14] speaks of a woman whose hair grows at the "prodigious rate of a half-inch per month." Half an inch per month is the average rate. --Sarah Shaftman, Madison, Wisconsin

When you're losing hair as fast as Cecil is, sweetie, any growth rate is prodigious.

AND NOW, A VERITABLE FEAST OF CROW

You were skeptical that J.R. could see the stroboscopic illusion of reverse rotation while looking out of his car at the wheels of other cars [October 27]. You said this illusion is usually only visible in movies. Actually, there's nothing surprising about what he saw if the cars were illuminated by artificial lighting rather than sunlight. When powered by alternating current, gas discharge lamps (which include neon, mercury vapor, sodium vapor and fluorescent tubes) flicker at twice the frequency of the power line (i.e., 120 times per second on a standard 60 cycle line). In each cycle of current the power peaks twice (once with positive voltage and once with negative) and twice goes to zero, and the light output varies accordingly.

Though 120 flickers per second is too fast for us to perceive directly, such lamps can produce stroboscopic effects. Mercury and sodium vapor lamps are widely used for street lighting, and under such lights J.R. could easily have seen what he said he saw. The effect may be less intense under fluorescent lights because the fluorescence does not die away completely between each half-cycle, but you may be able to see it if you play with a variable-speed fan lit only by fluorescent light. (I've often seen the effect with centrifuges in fluorescently-lit labs.) Incandescent bulbs have very little flicker because the filament doesn't cool off much in 1/120th of a second. --Barry Gehm, PhD, Chicago

"Fluorescently-lit labs"? Such language. Nonetheless, Barry, Cecil is prepared to concede you're right, not because you're a PhD--hey, we all God's chillun roun' here--but because he and Mrs. Adams spent a hair-raising hour driving like maniacs on the expressways trying to find out if the phenomenon in question actually occurs. Alas (for me), it does.

To tell you the truth, Mrs. Adams raised the possibility of reverse rotation being caused by flickering street lights. But I blithely dismissed the idea on the grounds that what most people think is reverse rotation is really just reflections off the hubcaps from "passing" street lights. Indeed, having done the research, I remain convinced that nine times out of ten that's what they are seeing. The tenth time, though, no question they're seeing a genuine strobe effect.

For best results, check out a car whose hubcaps have eight dark cutouts near the rim (Thunderbirds, Merkurs, and Renault Alliances fill the bill, we've noticed). You want to focus on dark stuff so you won't be deceived by reflections. On a car with wheels 22 inches in diameter, the cutouts will appear stationary at 59 MPH. If the car speeds up from 59, they will appear to rotate slightly forward--something that never happens with reflections.

I will have you know, incidentally, that I got a dozen letters on this topic in a single mail. You guys are such wankers. At the Straight Dope, however, we don't let mere ego get in the way of the facts.

Art accompanying story in printed newspaper (not available in this archive): illustration/Slug Signorino.

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