"I shouldn't wonder if he is right," said the other gentleman: "that often happens to car-wheels on a fast train, and we have been driving pretty fast, you know."
"Well, young man," said the other gentleman, "since you know so much about wheels, can you tell me why this wheel should act so, while the others are all right?"
"I presume it wasn't greased so well as the others," replied Johnny.
Just then a man who was passing by stopped to see what was the matter: he was a mechanic coming home from the rifle-factory, which closed at five o'clock. He asked a few questions, looked at the wheel, and said, "Oh! that's a hot wheel: you'll have to prop the carriage up, and pound it off from the axle. You've been doing a little blacksmithing as you came along. I presume the wheel and the axle are pretty neatly welded together, but yet not so much so but that a little artificial blacksmithing will set it all right again."
Then there was considerable stirring about: the carriage was propped up under the directions of the mechanic, and, after a good deal of hammering, the wheel was pronounced all right. Johnny brought out an oil-can; and, after the wheel was well oiled, the gentleman thanked everybody around, and offered to pay all who had helped, including Johnny. But every one refused to take any pay, except two or three boys who had hindered more than they had helped.
"That was a pretty good illustration of the effect of friction," said Alec.
"Yes," replied Johnny. "Now let us go in and make the gas."
"I sha'n't be able to stop any longer now, thank you," said Alec, "as my father told me to be home by half-past five. But I'll get a pipe and fix it myself, if I can find a piece of the right kind of coal, and that will save your pipe until another time."
"Sawdust, or almost any thing that will burn well, will answer to fill it with," said Johnny.
"I am ever so much obliged for your illustrated lecture," said Alec. "I've learned a good deal, and I wish you would come over to our house some day before long. I can't perform many experiments yet, but we'll have a good time somehow. I mean to begin to perform experiments, and study up about these things. I am two years older than you are, but I don't know half as much as you do."