r, what is the reason?"

"I don't know," said his father.

"Don't you know, father?" said Rollo. "I thought you were going to tell
us all about it."

"No," said his father. "I only know a very little about it, myself. I am
going to explain to you some of the facts,--such as I happen to know. So
you must all remember this fact, that in the magnet, the attractive
power is not distributed over the whole mass, but resides only in the
opposite ends. These ends are called _poles_."

"Yes, sir," said Rollo, "we will remember."

"Now I can make this apparent in another way," said his father. Then he
asked Rollo's mother to thread a needle; and when it was threaded, he
asked Jonas to stand up and hold the thread in such a manner as to let
the needle hang over the middle of the table.

Then, when the needle was still, he brought up the middle of the magnet
very near to the needle; but it did not move towards it at all. Then he
drew the magnet along towards himself, keeping it at the same distance
from the needle, and when the end of the bar came opposite to the
needle, it immediately leaped out of its place, and adhered strongly to
it.

"There is another way still," continued the lecturer, "better than
either of these."

So saying, he took off the needle, which had adhered to the magnet, and
drawing out the thread, he laid the needle itself carefully away upon a
distant corner of the table. Rollo took it up, and was going to place it
back with the others. But his father told him to put it down again, by
itself, where he had placed it, and not to touch any of the things
without his direction.

"I am going to show you another way," he added, "of making it evident
that the attractive power of the magnet resides at or near the poles."

So saying, he opened the sheet of paper, and spread it out upon the
table. Then he laid the magnet down upon it.

"Now, Jonas," said he, "sprinkle some sand upon it from my sand-box,
carefully, and see where the sand will adhere."

So Jonas took the sand-box, and held it over the bar, not very high, and
moved it slowly along, from one end to the other, and thus sanded the
magnet all over. The sand fell off of it, however, freely, at every part
except the ends; and Jonas, observing that it seemed to adhere there,
held the sand-box a little longer over those places; and thus there was
formed a sort of a black bur at the extremities, consisting of an
accumulation of the black particles of s