"This is how he did it. He put an apple and a turnip on the table, and side by side with them, pieces of chalk, cork, wood, lead, iron, flint, steel, and glass. Then he set one of the boys to try and scratch these things with his nail, one after the other. He could pick pieces out of the turnip and the apple; he could scratch the chalk, cork, wood, and lead; but he could not make the least mark on the iron, flint, steel, or glass.""I see," said Norah. "then this shows that the iron, steel, flint, and glass are harder than the wood and the lead; and that the wood and the lead are harder than the apple and the turnip.""You are a sharp little sister," said Fred, "and you are quite right.
"Teacher next gave the boy a knife, and askedhim to cut these things. He could cut little pieces off the lead and the wood, but he could not even scratch the steel, flint, or glass.""That was a good way, Fred," said Willie, "to find out which were the hardest things, by rubbing them one against another.""Yes," said Fred, "the steel, flint, and glass rub pieces out of the wood and the lead, because they are harder than the wood and lead.