Imagine a family of mice who lived all their lives in a large piano. To them in their piano-world came the music of the instrument, filling all the dark spaces with sound and harmony. At first the mice were impressed by it. They drew comfort and wonder from the thought that there was Someone who made the music—though invisible to them—above, yet close to them. They loved to think of the Great Player whom they could not see. Then one day a daring mouse climbed up part of the piano and returned very thoughtful. He had found out how the music was made. Wires were the secret; tightly stretched wires of graduated lengths which trembled and vibrated. They must revise all their old beliefs; none but the most conservative could any longer believe in the Unseen Player. Later, another explorer carried the explanation further.