What does Felix’ bath make him think about Prospero and Miranda?

Felix gets in his bath and says that Miranda is never there when he bathes, and this makes him think about Prospero and Miranda on their island. He says that Prospero must have locked up Caliban while Miranda was bathing, but that he himself could not take off his magic robe to bathe, since he would lose his magic, and so lose control of the island. He concludes that Prospero must not have bathed.