3 small equal-sized candles

3 small candleholders

1 small glass jar (that will fit over one of the candles)

1 large glass jar

Matches

The candle not covered by a jar burns for the longest time. The candle under the larger jar burns longer than the candle in the smaller jar. Fire will not burn without oxygen from the air. Once the oxygen is burned up the flame goes out. There is more oxygen in the larger jar than in the smaller jar. The oxygen supply is not limited for the candle without a jar.