Uncle George lit a piece of brown paper. “You will understand it now,” he said, as he held smoking paper near the top of the chimney.
Then the boys saw a stream of smoke go down one side of the card and come up the other side.
“Oh, I see it now,” said Tom. “The card divides the chimney into two. The air, heated by the candle flame, rises up one side of the card, and the cold air goes down the other side to supply its place, drawing the smoke with it. The candle does not go out now, because it gets a constant stream of fresh air.”
“Are the balloons, which are large enough to carry people, fire-balloons?” asked Dolly.
“No, my dear,” replied Uncle George. “They are filled with a gas that is lighter—very much lighter—than the air. They rise up easily, and can carry quite a heavy load.”
Questions and Exercises.
1. Take an empty bottle and heat it gently. Now turn it upside down, and place the neck of it in cold water. Why does the water rise in the bottle? 2. How is a draught caused? 3. Why does a fire burn more brightly on a cold, frosty day, than on a warm summer’s day?
IX.—THE GULL.
Frank, Tom, and Dolly had never seen the sea. Long ago Uncle George had told them that he would take them, and at last the time came for them to go.
It was afternoon when they reached the little sea-side village where they were to spend a few days. The children were filled with wonder when they saw the great, restless ocean. They watched the waves breaking into white surf, and gathered sea-weeds and shells on the sandy beach.