ith the back of his hand.

"You bet the sun's hot," the boy agreed, "but Mr. Levin told me the
other day that we only get a two-billionth part of the heat put out by
the sun. Did you know that, Ross? The sun has heat enough to warm two
billion Earths as big as this one. Even at that, Dan'l, the amount of
heat we get from the sun would make thirty-seven billion tons of
freezing water boil in one minute."

The negro's jaw dropped.

"Yo' not fooling?" he said.

"Not a bit."

"Ah's hot," he said. "Ah's goin' to boil, soon."

"Cheer up, Dan'l. You'll cool off tonight," suggested the older lad.
"Nearly everything that takes in heat has to give it out again. The
earth, the sea and the dust in the air, all gradually let out some of
the heat during the night. If it wasn't for that, everything would stay
at the same temperature all night long. That's why it's always colder an
hour before dawn than an hour after sunset.

"See, Dan'l, the earth and the air which take in heat easily and give
off heat easily, by the end of the night, have got rid of a lot of their
heat. At sea, though, where the water lets go its heat less easily, it
is never as cold as on land. The thermometer shows when it's hot and
when it's cold."

"Ah don't hold with none o' them fermometers," the old darky repeated.

"That's because you don't understand them," the crippled lad replied.
"It's dead easy, though. You see, Dan'l, when a thing is hot it gets
bigger and when it's cold it gets smaller, that is, most things do."

"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. Sup