Old Grapejuice Stain,

Did you try again later? At first I had a typo in the URL so that FreeMars
couldn't find the GIF. A few minutes later I deleted the original file and
replaced it with one having a slightly slower frame rate. It works better
in my animation program and in my image viewer than it does in IE.

Moose,

Chemical refresh rate of the cone cells isn't really involved. It is just as
Delvo explains, the farther the lines are from the center, the farther they
jump between successive frames. So the jump near the center of the
image is only a couple of pixels -- much less than the size of a square --
while the jump near the edge of the image can be twenty or thirty pixels
or more -- larger than the size of a square. In parts of the image where
the jump is about equal to the size of a square, you identify one square
in one frame with a different square in the next frame. In the wagon
wheel illusion, you identify each spoke in one frame with a different spoke
in the next frame.

-- Jeff, in Minneapolis

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"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves