For a simple illusion that can be part of a science fair project, this self-explanatory diagram shows how to make a candle look like it’s burning inside a bottle of water.

A plate of glass is placed as shown.  Since it allows light to pass through, but also reflects light, when it’s viewed at the correct angle, it appears that the candle is inside the bottle of water.

This idea appeared 85 years ago this month in the February 1937 issue of Popular Science.