A box is made with a glass front and two glass chimneys. When air is heated, it expands and becomes less dense than the air around it. By Archimedes principle, this less dense air will rise (hot air rises). When a candle is lit on one side of the apparatus, the air directly above it rises. The air in the other chimney falls. Burning touch paper (which produces much smoke) held above the chimney without the candle under it will show the direction of the air current.
|Convection apparatus with touch paper and small candle||017-6C|