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Re: stroboscopic eyes

On Thu, 30 Jan 1997, Ken Fox wrote:

The jarring head explanation I believe is least likely for the effect as
described to me by students. That would need more vibration than most car's
I'd ride in give on pavement. I could not observe the effect yesterday and
my colleague maintains it is most likely the vapor lights...so the
experiment goes on.

I think the claim that wagon wheels sometimes appear go backwards is
bordering on urban legend status.

I first encountered it in 1986 or so, when a college simply would not
believe that airplane propellors did not contain a "ghost" image which
rotated slowly forwards or back. He was remembering TV movies (possibly
WWII shows, since how often do we see prop-driven aircraft, even on TV!)
Since becoming "sensitized" to this issue, I've encountered people
(usually on internet) who swore that they personally saw wagon wheels turn
backwards, railroad ties move slowly while the train moves fast, etc. But
me, I've been specifically looking for just these effects, and I
*constantly* see them on TV or in the movies, but *never* see them in the
real world.

The closest I've been to seeing the purported effect was in, as has been
mentioned, chrome wheel hubs. If you watch a car go by you, the viewing
angle and angle to the sun continuously changes, and this can make the
"ghost image" caused by rotary scanned reflectors within the wheel hub
appear to rotate slowly. But the apparent motion never completes a full
revolution, just as you'd expect.

One question for your doubting audience: Where exactly did they see a real
wagon driving down the street? Wagon wheels are common on TV, but very
rare in most parts of the everyday world.

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