“He was making something long,” answered Billy.
“We make lathes,” said Mr. Prescott. “Good ones; all kinds.”
In the next room he stopped again.
“Different kinds of iron,” he said. “Some much harder than others, like tool steel. Iron cuts iron. That’s a planing machine: automatic plane cuts any thickness.”
Billy stopped beside the mighty planer, moving over the large casting as easily as if the iron had been wood and the fierce chisel only a carpenter’s plane.
They went on a little further, then Mr. Prescott turned suddenly. “William,” he asked, “how long is an inch?”
He certainly had sprung it on Billy, but Billy’s spring worked too.
“About down to there,” he answered, marking his left forefinger off with his right. “No,” he said, moving his mark up a little higher, “about there.”
“You were nearer right the first time,” said Mr. Prescott. “Now, listen to me. Iron can cut iron to within a fraction of a thousandth of an inch.”
Billy’s eyes opened till they showed almost twice as much white as blue.