“Automatic index registers. Man watches index.
“Look at that,” he said a moment later. “See that machine cutting a screw.”
That seemed to be something that especially interested Mr. Prescott, for he stood a moment to watch the tool that was cutting into the round bar of iron, making, in even and regular grooves, a huge screw. Automatically, too, there came down on it a steady stream of oil.
“Why’s that?” asked Billy.
“The oil keeps the iron from becoming too hot,” answered Mr. Prescott. “Heat expands iron. If we didn’t keep it cool, the screw wouldn’t be the right size when it is done.
“Cold naturally works the other way. Ever hear about the iron bridge where the parts wouldn’t quite come together, so they put ice on to do the job?” he asked, but he kept right on, without waiting for Billy to answer.
Billy saw other machines boring holes and rounding corners. It seemed as if iron could cut iron into any shape that anybody wanted.
Then there were men polishing and polishing, until they could fairly see their faces in the iron. Billy could hardly believe that the gray iron of the foundry could ever have become such silver-shining iron.
Still Mr. Prescott kept on, Billy close behind.
“This,” said Mr. Prescott, stopping in a room almost at the end of the mill, “is the assembly room. Here is where the machines are put together.”