🚀 go-pugleaf

This is called the Pulfrich effect.  The Exploratorium in SF has exhibit
full of moving objects devoted to it.  According to the Exploratorium
Cookbook 1, "Visitors view a white ball that is oscillating back and
forth.  One eye has an unobstructed view and the other views the ball
through a layer of dark plastic.  Under these conditions, the ball
appears to move in a horizontal ellipse.  This illusion occurs because
the eye and brain take slightly longer to process the dimmer image.  The
eye that viewed the ball through dark plastic does not see the ball where
it is at a given moment, but rather where the ball was a short time
earlier."
They also suggest using two layers of dark plastic to change the delay.
                                                Bruce Ruble

On Sat, 7 May 1994 PHYS2SHS@URIACC.URI.EDU wrote:

> I recently saw a demonstration about a strang effect of pendulums when
> viewed through a filter.  If you take a piece of red plastic (plastic wrap
> works fine) and place it in front of one eye, leave the other eye uncovered,
> and view a swinging pendulum. It appears that the pendulum is moving in an
> eliptical shape instead of the expected side to side motion.  The person
> giving the demo could not explain why this happens.
>
> Any one have any ideas?  Try this yourself it is interesting!  ?:-|
>
>                             -Gregory R. Snow
>                              Smithfield High School
>