Lesson 07 Hard and Soft Bodies

We had a lesson today, said Fred, "about solid bodies—some hard and some soft. Teacher showed us that we can call a body hard or soft only when we set it side by side with some other body."

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 asked him 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."

The steel knife made a scratch on the iron, because it is harder than iron, but it could not scratch the glass.

The wood and the lead rub pieces out of the chalk and cork, because they are harder than chalk and cork.

And the chalk and cork rub pieces out of the apple and the turnip, because they are harder than the apple and turnip.

Glass must be very hard, said Will. "A steel knife will not even scratch it."

Teacher showed us that we can just manage to scratch glass with a sharp bit of flint, but we cannot cut it with flint.

I've seen a man cut glass, said Norah.

Yes, dear, said Will, "but he cuts it with a diamond, and diamond is the hardest of all bodies."

SUMMARY

Diamond is the hardest of all bodies. It will cut glass. A steel knife will not even scratch glass. Steel is harder than iron; iron is harder than lead; wood is harder than cork. The hard body will scratch a soft one.