"That's it," Daddy Blake answered. "And so, as the ice could not lift out the cork, it swelled to the sides, instead of to the top, and pushing out as hard as it could, it broke the bottle. The glass fell away, and left a little statue of ice, just the shape of the bottle, standing in its place.
"How wonderful!" cried Mab, her blue eyes open wide.
"Yes, the freezing of ice is very wonderful," Daddy Blake said, as he passed Hal his third slice of bread and jam. "If the cracks in a great rock became filled with water, and the water froze, the swelling of the ice would split the great, strong stone.
"There is scarcely anything that can stand against the swelling of freezing ice. If you filled a big, hollow cannon ball with water, and let it freeze, the ice would burst the iron."
"It burst our milk bottle once, I know," said Aunt Lolly.
"Yes," spoke Daddy Blake. "That is why, on cold mornings, the milkman raises the tin top on the bottle. That gives the frozen milk a chance to swell up out of the top, and saves the bottle from cracking."
"One morning last winter," said Mamma Blake, "when we had milk bottles with the pasteboard tops, the milk froze and there was a round bit of frozen milk sticking up out of the bottle, with the round pasteboard cover on top, like a hat."
"And that's what saved the bottle from breaking," said Daddy Blake, "If I had not wired down the cork of our bottle the water would have pushed itself up, after it was frozen, and would have stuck out of the bottle neck, like a round icicle."
"But what about our secret?" asked Hal. "Is it cold enough for you to tell us about it?"
"I think so," answered Daddy Blake, with a queer little twinkle in his eyes. "As long as the water in the bottle was frozen, the pond will soon be covered with ice," he said. "And we need ice to make use of the secret."