“The gas pushed it out,” said the Professor, “I told you how I stirred up the bottom of the pool. It was all covered with dead leaves. These as they rot give out gas, but it cannot easily escape from the bottom, and stays down among the leaves and slime till it is stirred up. Then the little bubbles of gas come popping up, and as they mount I am ready with my tumbler and saucer. I slip them both softly into the water a little way off, draw out the saucer, slide the inverted tumbler over the bubbles before they break; and the gas mounts into the tumbler, each bubble of gas displacing a little water; then over more bubbles, and more and more, until all the water in the tumbler is out and the gas is in its place; then I fill the saucer with water again, slide it under the tumbler, and bring it home.”
“Come to your luncheon, children,” cried nurse. “The pudding will be cold.”
“Oh, wait a minute,” said Tom. “You said the gas drove out the water in the tumbler. Why don’t it drive out the water in the saucer?”
The Professor looked puzzled.
“Well, it would in time, I suppose. But you see, its nature is to push upward, because it’s light——”
“Oh, now, it pushes the same every way,” said Tom.
“There’s something we don’t know,” said Bob.
“Oh, yeth, I am afwaid we don’t know it all,” said Pip.
“Well,” drawled the Professor, “I don’t know, only I guess it’s because the water is too dense—too close together, for one thing; and the same atmospheric pressure that kept the water in keeps the gas in, for another.”
“There, I do believe that’s it,” said Pip. “Oh, how nice it did pop off! Like a vewy small fwier-cracker a great way off. Now let’s have some pudding. Apple and sago! Just the nithest pudding in the world!”