"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. This attraction is what gives every thing weight.
"If I lift up any thing, I am acting against this force, for which reason the article seems heavy; and the more matter it contains, the greater is the force of attraction and the heavier it appears to me."
"Then," said Lucy, "if this attraction is so powerful, why do we not stick to the ground?"
"Because," replied her father, "we are animate beings, and have the power of motion, by which, to a limited degree, we overcome the attraction of the earth."
"Well then, father," said Lucy, "if our power of motion can overcome the attraction, why can not we jump a mile high as well as a foot?"