Wasn't it Patrick Elliott who wrote:
>In article <Av7### [at] econymdemoncouk>, 
>nos### [at] econymdemoncouk says...
>> If you replace the "plane {y,-5" with a box of finite thickness,
>> something like "box {<-1000,-1000,-1000><1000,-5,1000>" the chaotic
>> effect goes away.
>> 
>Though.. Technically, it isn't infinite, the plane bisects a sphere, so 
>the media is actually contained in that. Reducing the size of the sphere 
>to 10000 still produces the same oddities, though with some faint white 
>streaks in it, like the edges of ripples. 5000 and the whole thing starts 
>to get murky and darker, but the pattern never disappears and it starts 
>to look like some odd thing floating inside the media. I need a faster 
>computer.. lol But seriously, it doesn't seem to be a result of the 
>ambient on the sphere either... This is really odd.
>
>Hmm.. It gets less visible at a sphere size of 2000 and pretty much 
>vanishes, (in the sense that it is no longer a 'sharp edged' pattern), at 
>1000, though the resulting pattern is still showing complex oddities. It 
>is nothing like what a box produces. This definitely seems to be 
>*entirely* related to the choice of using a sphere and a plane to create 
>a container for the media. Definitely interesting, but very strange.

Yes. It's more complicated than I thought.

The effect doesn't appear when using a box, but it does appear when
using "difference {  plane {y, -5}  plane {y, -1000}" when the lower
plane is sufficiently distant. When using this difference, the sphere
can be replaced with "background {rgb 1}" and the effect remains exactly
the same.

-- 
Mike Williams
Gentleman of Leisure

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