"And so it would be—"
"One hundred forty-four," said Frank.
"Then," said Uncle Robert, "if there are one hundred forty-four square inches in one foot, how many in one thousand feet?"
"One hundred forty-four thousand," said Frank, after a moment's thought.
"But the rain-gauge says that an inch and a half of rain has fallen," said Uncle Robert, "and when an inch is as deep as it is long and broad, it is called a cubic inch. How much would one and one-half cubic inches be?"
"If this is one inch," said Frank, looking at the paper, "half an inch deep would be half of this, and that, added to this, would be an inch and a half. Isn't that right?"
He went to work again, and after a few minutes' silence he said:
"It makes two hundred and sixteen thousand inches in all."
"What kind of inches did we call them, Donald?"
"Cubic inches," said Donald.