During a two-hour drive yesterday, I kept searching (vainly) for a reproduction of my 
original observation about the wagon-wheel illusion.  It was a sunny day, so that 
variable differed.  But I'm not thinking that the suggestion by Dennis Goff that the 
speed - of the moving observer as well as the wheel observed - might be a factor.  But 
most importantly, I'm convinced that the rear-view mirror had SOMETHING to do with the 
effect.  

I challenge others, while they're driving, to CAREFULLY look in the rear-view mirror 
as a truck is approaching you - in the passing lane.  What you're looking for is the 
kind of big truck with those lug-nut things on the front wheel.  (Keep watching the 
road in between those glances!!)  What's interesting is that the spinning lug-nuts on 
the wheel look different in the mirror than they do when you glance at them through 
the window as the truck gets closer.  I didn't get the wagon-wheel effect, but they 
seemed to spin in an interesting way that I didn't see when watching through the 
window.

I recalled again the possibility that it's the rear-view mirror, which has different 
engineering design than the side mirrors because it can be adjusted for nighttime, 
that might be involved.

Please be careful when doing this.  I don't want to read about anyone being involved 
in an accident while doing scientific research!!
Beth Benoit
University System of New Hampshire

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