He kept his books, which chiefly treated of magic, a study at that time much affected by all learned men: and the knowledge of this art he found very useful to him; for being thrown by a strange Chance upon this island, which had been enchanted by a witch called Sycorax, who died there a short time before his arrival, Prospero, by virtue of his art, released many good spirits that Sycorax had imprisoned in the bodies of large trees, because they had refused to execute her wicked commands. These gentle spirits were ever after obedient to the will of Prospero. Of these Ariel was the Chief.