Now let us return to the first scene provided with this pass-key. It unlocks that and all the subsequent supernature which had a relish for his society. We feel that the witches express the moral condition of Macbeth's mind, its tumultuous hesitation that is on the point of settling into the definiteness of crime,--"Fair is foul, and foul is fair." All moral discriminations are huddled together and dislocated by the upheaval of his subterranean motive. He really sends these witches forth to a blasted heath, the avant-couriers of his own visit thither, and of a longing that gains substance and direction the more he entertains it. It is strong enough to be an object behind his retina; and it throws out shapes to limn themselves upon the air into which they make themselves and vanish. And they can appear only at that period of his evil brooding when it gathers and swells, too big for his brain, bursting its barriers to become external. After the actual murder of Duncan has occurred, the brain of Macbeth is depleted for a while: the ominous forms wait till Banquo's ghost can recruit them. Macbeth has an imagination so keen and unbridled that it outruns the limits of thinking, to become projected outside of his bodily eye in shapes and objects that occupy the focus of his criminal intent. His crimes become ocular deceptions, because they are so palpably real to his mental vision, sharpened as it is by the ambitious sympathy of a wife whose temperament outraces action. Murder is Macbeth's owner before he is conscious that he has made himself the chattel of his wife's suggestions. That same creative fancy built forth into the air the handle of the instrument which he has fated himself to use: he marshalled it the way that he intended to go. No supernatural smith has forged the fatal weapon: it is tempered in the current of his own plastic mind. But although Macbeth has this mobile imagination, like that which "If it would but apprehend some joy, It comprehends some bringer of that joy;" and though he has become one of those madmen who "Have such seething brains, Such shaping fantasies, that apprehend More than cool reason ever comprehends," he is still capable of reverting to this cool reason, at least so far as to appreciate that his desperate dreams are the poetry of desperate consequences which will tax all his waking powers. When the apparitions vanish, in Act iv. 1, one of the witches gives a voice to Macbeth's perturbation; but why "Stands Macbeth thus amazedly?" It was but the voice of revulsion from amazement, to "cheer up his sprites" and summon resolution. When Macbeth originates any thing out of himself, that Self is not daunted, for it is too deeply compromised in fact and fancy. But when some phenomenon threatens him from a quarter that is outside the limit of his own creative power, as when Birnam Wood is descried coming toward Dunsinane, he is puzzled, and says:--