Prospero's cloak and books are the source of his power. He deliberately takes off his cloak at two points in the play: once when he tells Miranda
of their history, and again at the end of the play when he gives up his magic. Gonzalo
knows how much Prospero loves his books, and he arranges for them to be placed on the ship that removes Prospero and Miranda from Milan. Without the books, Prospero would not have had the power to summon the tempest and restore order to Milan and Naples. Caliban
to seize Prospero's books when they make plans to murder Prospero and take control of the island. When Prospero relinquishes his magic at the end of the play, he says, "I'll drown my book" (5.1.57). If, as many critics suggest, Prospero is the voice of Shakespeare as he retires from the theater, the books might also represent the power of words and ideas.