He ambled up to Ross, who was busily shovelling in the earth. "Hyar, Mist' Ross," he said, "let me do that for yo'. Yo' ought to ask old Dan'l when yo' got a job like that." "That's all right," the older boy answered, readily yielding up the spade, however, and wiping the perspiration from his brow, "it is pretty hot, though." "Yo' got no call to be workin' right near noon," the negro protested, "that's not fo' white folks. Fust thing yo' know, yo'll be havin' a sunstroke." He shoveled vigorously as he talked, tamping the earth down hard. "It's sho' goin' to be a hot summer," he said, "yo' only find the field-mouse nests where the shadder's thickest. Thar," he continued, patting down the earth level with his spade, "that's done now. Yas, suh, it's hot." He wiped the perspiration from his forehead with 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?"