"This is a funny doorstep," she remarked, to kill time.
"It's of marble," said Denry.
"What's that for?" asked his mother.
"So much easier to keep clean," said Denry. "No stoning to do."
"Well," said Mrs. Machin. "It's pretty dirty now, anyway."
It was.
"Quite simple to clean," said Denry, bending down. "You just turn this tap at the side. You see, it's so arranged that it sends a flat jet along the step. Stand off a second."
He turned the tap, and the step was washed pure in a moment.
"How is it that that water steams?" Mrs. Machin demanded.
"Because it's hot," said Denry. "Did you ever know water steam for any other reason?"