Goldfish bowl reflecting inside into apparent 3-D

[Nick Levinson]

I saw an optical illusion once decades ago that I don't think I've seen written up anywhere else. I don't even know what to call it, so I can't very well Google it.

A box about three feet tall and about a foot square on top had a large hole on top. Looking down inside it, we could see a jewel. An invitation to help ourselves was posted and a nice person told us to go ahead. We tried. My hand went through the jewel like it didn't exist. Then we read the sign in small print.

Basically, in the top of the box was something like a goldfish bowl, but it was coated on the outside so that it had mirror surfacing inside. The jewel was way down at the bottom. What we saw was near the top, so we reached near the top and I felt nothing and my friend probably felt nothing, too. The explanation in the sign was that the jewel was being reflected from the bottom to the top, thus was only an optical illusion at the top.

My problem with this explanation is that, by now, I should have seen or heard or read of dozens of similar illusions in various places.

What was really going on?

 

[phinds]

I've forgotten the exact description but it's a simple effect of curved mirrors and precise placement of the object. I also can't help with the name but I'm sure there are dozens of illustrations on the internet if we knew what to look for.

 

[Ibix]

http://practicalphysics.org/optical-illusion-concave-mirror.html?