I’d like to point out an interesting illusion I discovered by accident with my good friend Tom a number of years ago.

I was showing him photographs in Stokes’ Geology of Utah. One shot was a black–and–white aerial view of the Goosenecks of the San Juan River. We were sitting at a table, across from each other, with the book set between us.

I pointed to the river.

He responded, “What river?”

I said, “That river there. That’s the San Juan River.”

He responded again, “I just don’t see which river you’re talking about.”

Confused for a moment, I decided I should take a look from his point of view. The book was oriented so the right side up was in line with my view and he was looking at it upside down.

When I flipped it around and looked at it upside down, I realized why he wasn’t seeing it!

Below I have photographed the page in Stokes’ book and then also rotated the image to demonstrate the illusion.

click to zoom

original photo: US Bureau of Reclamation

If you happen to have Stokes’ book (or print out the image or use a tablet), try the following:

Place the book/image upside down ... then slowly rotate the book around and see if you can maintain the illusion, before it snaps back.

Once it snaps back, can you make it revert again?

I can’t.


stefan

© 2005 Stefanos Folias (text),
Photo © U.S. Bureau of Reclamation,
In: W. L. Stokes, Geology of Utah,
University of Utah Press, 1986