A few weeks ago I wrote about "The Origami Mind" and I listed a number of other interests that are likely to appeal to paperfolders, including amongst others, cats' cradles. knotting, conjuring, recreational mathematics, tessellations, labyrinths and puzzles.

I was reminded of another such interest yesterday, when I happened to find book in a remainder bookshop here in Grimsby.

This was: Bruno Ernst: Optical Illusions, published by the well-known German art publishers, Taschen of Cologne, (with branches in London, New York, Lisbon, Osaka and Paris).

The date appears to be 1989, but this may have been the date of the German edition, not the English translation. !SBN 3-8228-9637-3. An A4-sized paperback.

I have been collecting books on optical illusions for many years, but I think I can say that this is the best one I have come across so far and I would recommend it to anyone already interested in the subject or still to become interested. For people resident in Britain, it can be had from branches of "The Works" for only 3.99 UK pounds, and I reckon it is a bargain.

Bruno Ernst has written at least two other books on the same subject:

Adventures with Impossible Figures: Tarquin Publications, Diss, England, 1985. (Tarquin publish a fascinating collection of books on subjects that are likely to appeal to the origami mind, including, curiously enough, books on paperfolding.)

and

"The Eye Beguiled". 1986. [I regret that this book has buried itself somewhere and has no desire to revel its whereabouts so I can't give any other particulars at the moment.]

Bruno Ernst has also written a book on MC. Escher, famous for his use of optical illusions. This is "The Magic Mirror of M.C. Escher, published in 1985. This is another excellent book.

Incidentally, it is revealed in "Optical Illusions" that "Bruno Ernst is the pen-name of a Dutchman whose real name is J.A.F.Rijk but my search in Alta Vista against that name produced no replies.

What inspired me to write about this is that the long bibliography to "Optical Illusions" lists three papers by D.A Huffman from the journal "Machine Intelligence" and another from Computer vision Systems, all relevant to optical illusions.

It so happens that David Huffman is also an innovative paperfolder, who has done experiments in folding using curved lines.He keeps himself somewhat apart from the main stream of paperfolding, but he has a Web page of his foldings at:

http://www.sgi.com/grafica/huffman/

This amply repays inspection and study and I think it vindictes my idea that people who are attracted to origami are also attracted to optical illusions.

Searches in Aalta Vista agains both Bruno Ernst and D.A.Huffman yield numerous interesting sites. Alta Vista claims to have 4260 sites about Optical Illusions.

David Lister