“I should think two names were enough for nothing,” says Bob.
“What’th the other name?” said Pip.
“Ignis fatuus,” said the Professor. “It means ‘Cheating-fire.’ Sometimes this gas, rising to the top of the water in bubbles, takes fire (by what they call spontaneous combustion, or by mixing with some other gas, or in some other way), and then, as one bubble after another takes fire and goes flickering along, it looks as if some one were walking through the woods with a lantern.”
“And thath how it cheat-th, isn’t it?” said Pip. “But I don’t thee how it is thet afire. Perhapth, now—perhapth it’s the fire-flyth!”
“Oh, good for you!” said the Professor; and he chased her round the table, and caught her, and kissed her.
“Well, how did you ever get it with that tumbler?” said Tom.
“Well, easy enough. First, I filled the tumbler with water. Then I laid the saucer over the top. Then I plunged the whole under the water, holding tumbler and saucer with both hands firm, and turned them over in the water, and drew them out. The saucer, as well as the tumbler, was then full of water, and though the tumbler was upside down the water couldn’t fall out.”
“What hindered it, I’d like to know?” said Bob.
“Atmospheric pressure,” said the Professor, pushing the words out slowly. “The whole atmosphere weighs down on the water in the saucer and balances the water in the tumbler and keeps it in.”
“It had all leaked out before you reached home, anyway,” said Bob.