I said, as he looked up with a scared expression. "It
isn't broken. Put the bar back."

Charlie put it back, and it sprung into place with a sharp click.

"That's funny!" he cried again. "What made it jump so? And what makes it
stick? It doesn't feel sticky."

"We call it magnetism," I said. "Now, take hold of the bar, and see if
you can pull it straight off."

"I can't. It sticks fast."

"Pull harder."

Charlie braced himself for a strong pull. Suddenly the bar came off, and
he went tumbling backward.

"What did you say makes it hold so hard?" said he, getting up.

"Magnetism," said I again.

"But what is magnetism?"

"I couldn't tell you if I tried; but I think you could learn a great
deal about it with that magnet. You will find a lot of things in that
box that may help you."

Saying this, I left him to pursue his studies as best he could. When I
came back, I found him more puzzled than when I left him.

"That's the queerest thing I ever saw," he said. "Some things just jump
at it as though they were alive; some things it pulls; and some things
it doesn't pull a bit."

"That's a very long lesson you have learned," I said. "What does it
pull?"

"These," he said, pointing to a pile of things on one side of the box.
"And these things it doesn't pull."

"Let us see what you have in this pile," I said, looking at the first
little heap; "keys?"

"Trunk keys," said Charlie. "It doesn't pull door keys. I tried ever so
many."

"Try this key," said I, taking one from my pocket. "This is a trunk key.
See if the magnet pulls it."

"No-o," said Charlie, thoughtfully, "it doesn't; but it pulled all the
rest of the trunk keys I could find."

"Try this key to my office door."

Charlie tried it, and to his great amazement the key stuck fast to the
magnet.

"Surely," said I, "it pulls some door keys, and fails to pull some trunk
keys."

Charlie was more puzzled than ever. He looked at the keys, thought a
moment, then picked up my trunk key, and said: "This key is brass; the
rest are iron."

"That's so," I said.

"And all these door keys that the magnet didn't pull," he continued,
"are brass, too. Perhaps it can't pull brass things."

"Suppose you try. But first see if there are any brass things that the
magnet pulled."

Charlie looked them over. Then we tried the casters of my chair, and all
the other brass things we could find, none of which the magnet would
pull.

"There's no use in trying an