Candle in Stoppered Jar—burning.
“Then I must explain,” said Uncle George.
“Some of the air has gone,” said Tom.
“Yes,” said Uncle George. “How much of the air has gone?”
Frank pointed to the space between the two marks.
“That is right,” said Uncle George. “The water has risen up in the bell-jar to take the place of the air that has been used up by the burning of the candle. Where has this used-up air gone?”
“It must have gone into the water,” said Tom.
“Why did it not go into the water before the candle burned?”
“Perhaps the burning of the candle has changed this part of the air,” said Frank.