[JeffF.]

in the Silmarillion chapter called Akallabeth, near the end, Tolkien wirtes that (in the fall of Numenor) " Sauron was robbed of that shape in which he had wrought so great an evil, so that he could never again appear fair to the eyes of men...he wrought himself a new guise, an image of malice and hatred made visible: and the Eye of Sauron the Terrible few could endure."

thie is reiterated again in the chapter Of the Rings of Power and the Third Age, "he had wrought for himself a new shape: and it was terrible, for his fair semblance had departed forever when he was cast into the abyss at the drowning of Numenor. He took up again the great Ring and clothed himself in power; and the malice of the Eye of Sauron few even of the great among Elves and Men could endure."