how do Moving Waterfall Pictures work

Does anyone know ho these cheesey moving waterfall pictures work?
e.g http://www.moving-waterfall-pictures.com /
I know that they contain a motor and I remember seeing something similar on lampshades when I was a kid, but never managed to get close up to take one apart ( I think that Boots would have objected)
Thanks!
Bramblestick
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Does anyone know who would possess the complete lack of taste needed to buy such things?
I have only seen them in ethnic takeaways and restaurants, and mostly back in the 1970s.
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wrote:

Absolutely agree - I wouldn't part with money for one. Just interested in how they work, so that I can see if I can build one. At least it will be a DIY taste fail - I'm of the Readers Digest Manual and Alternative London school of DIY so taste is compromised anyway :-)
Bramblestick
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Look up Moire pattern like

http://uk.youtube.com/watch?v=lqSVUYWoabY

HTH Adam
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Adam Aglionby wrote:

Which are (were?) also used for measuring cows. Seriously.
Can't remember the details but something like projecting two sets of fine lines onto a cow - the resulting moire fringes highlighted the shape of a cow.
--
Rod

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wrote:

Excellent! Thanks for that - I'll have some fun playing around (already demonstrated it to myself using a folded piece of silk...), and hopefully the results won't be totally tasteless.
Bramblestick
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