"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.
Lesson 08
Porous Bodies
"I wish," said Fred, "every fellow in my class had a jolly little sister, like I"ve got, to play school in the evenings. "We had a fine lesson on a sponge today. Wouldyou like us to tell you all about it, Norah?" "That I should," said his sister.
