"Ah don't see that, nohow," the negro answered. "A red hot stove is just 'zackly the same size as when the fire's out."
"No, it isn't, as a matter of fact," the lad replied, "but you can't always see the difference. Iron does get bigger as it gets hot. You've seen the steel rails on railroad tracks, haven't you, Dan'l."
"Sho'."
"Did you ever notice that there's a little crack between each rail? In winter, the crack is quite wide."
The negro thought for a moment.
"Is that the crack that makes a train bump?"
"Yes, that's it. Now, Dan'l, on a hot day in summer, you can't see any crack there at all, the rail has expanded or got bigger, and filled it up. On a frosty day in winter, there's a big crack, so big that you could drop a lead pencil between the ends of the rails. That's the difference of expansion on a steel rail between winter and summer."
"That's powehful little!"
"It's quite a good deal. I'll show you. Suppose, Dan'l, you had a small rubber ball filled with ink and there was a pipe out of the ball sticking straight up in the air, and suppose you put that little rubber ball in the crack between the rails."
"Yes?"