"And what is it?" asked Lucy.
"If things away from the earth can not move themselves to it," said her
father, "there can be no other cause of their falling than that the
earth pulls them."
"But," said Lucy, "the earth is no more animate than they are; so how
can it pull?"
"That is not an ordinary question, but I will try an explanation," said
her father. "Sir Isaac Newton discovered that there was a law in nature
called attraction, and that all bodies exert this force upon each
other. The greater the body, the greater is its power of attraction.
"Now, the earth is an immense mass of matter, with which nothing near it
can compare in size. It draws therefore with mighty force all things
within its reach, which is the cause of their falling. Do you understand
this?"
"I think that I do," said Lucy; "the earth is like a great magnet."
"Yes," said her father; "but the attraction of the magnet is of a
particular kind and is only over iron, while the attraction of the earth
acts upon every thing alike."
"Then it is pulling you and me at this moment!" said Lucy.
"Certainly it is," replied her father; "and as I am the larger, it is
pulling me with more force than it is pulling you.
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