HOW TO DO THE TRICK
Explain that just as a glass prism splits up the different colours of white light, when different coloured light passes through glass, it is also affected to an extent that depends on its colour.
Write the words CARBON DIOXIDE on a piece of paper, CARBON in red and DIOXIDE in blue. Put the paper close behind the stem of a wine glass, and look at the words through the stem. The red letters turn upside down, but the blue ones don’t.
So is the glass affecting the red light more than the blue?
HOW IT WORKS
You weren’t fooled, were you? This has nothing to do with the different colours of the words, or of red light being bent more or less than blue light.
The stem of the wine glass turns both words upside down, but because DIOXIDE is symmetrical about a horizontal line, you don’t notice that it is upside down - it looks just the same either way.