11.10.09

**The artist M. C. Escher was influenced by your geometric inventions. What was the story there?**

In my second year as a graduate student at Cambridge, I attended the International Congress of Mathematicians in Amsterdam. I remember seeing one of the lecturers there I knew quite well, and he had this catalog. On the front of it was the Escher picture *Day and Night*, the one with birds going in opposite directions. The scenery is nighttime on one side and daytime on the other. I remember being intrigued by this, and I asked him where he got it. He said, “Oh, well, there’s an exhibition you might be interested in of some artist called Escher.” So I went and was very taken by these very weird and wonderful things that I’d never seen anything like. I decided to try and draw some impossible scenes myself and came up with this thing that’s referred to as a tri-bar. It’s a triangle that looks like a three-dimensional object, but actually it’s impossible for it to be three-dimensional. I showed it to my father and he worked out some impossible buildings and things. Then we published an article in the *British Journal of Psychology* on this stuff and acknowledged Escher.

**Escher saw the article and was inspired by it?**

He used two things from the article. One was the tri-bar, used in his lithograph called *Waterfall*. Another was the impossible staircase, which my father had worked on and designed. Escher used it in *Ascending and Descending*, with monks going round and round the stairs. I met Escher once, and I gave him some tiles that will make a repeating pattern, but not until you’ve got 12 of them fitted together. He did this, and then he wrote to me and asked me how it was done—what was it based on? So I showed him a kind of bird shape that did this, and he incorporated it into what I believe is the last picture he ever produced, called *Ghosts*.

### Autoria e outros dados (tags, etc)