Now all these agencies—­darkness, the lights and colours that illuminate it, the storm that rushes through it, the violent and gigantic images—­conspire with the appearances of the Witches and the Ghost to awaken horror, and in some degree also a supernatural dread.  And to this effect other influences contribute.  The pictures called up by the mere words of the Witches stir the same feelings,—­those, for example, of the spell-bound sailor driven tempest-tost for nine times nine weary weeks, and never visited by sleep night or day; of the drop of poisonous foam that forms on the moon, and, falling to earth, is collected for pernicious ends; of the sweltering venom of the toad, the finger of the babe killed at its birth by its own mother, the tricklings from the murderer’s gibbet.  In Nature, again, something is felt to be at work, sympathetic with human guilt and supernatural malice.  She labours with portents.

     Lamentings heard in the air, strange screams of death,
     And prophesying with accents terrible,

burst from her.  The owl clamours all through the night; Duncan’s horses devour each other in frenzy; the dawn comes, but no light with it.  Common sights and sounds, the crying of crickets, the croak of the raven, the light thickening after sunset, the home-coming of the rooks, are all ominous.  Then, as if to deepen these impressions, Shakespeare has concentrated attention on the obscurer regions of man’s being, on phenomena which make it seem that he is in the power of secret forces lurking below, and independent of his consciousness and will:  such as the relapse of Macbeth from conversation into a reverie, during which he gazes fascinated at the image of murder drawing closer and closer; the writing on his face of strange things he never meant to show; the pressure of imagination heightening into illusion, like the vision of a dagger in the air, at first bright, then suddenly splashed with blood, or the sound of a voice that cried ‘Sleep no more’ and would not be silenced.[196] To these are added other, and constant, allusions to sleep, man’s strange half-conscious life; to the misery of its withholding; to the terrible dreams of remorse; to the cursed thoughts from which Banquo is free by day, but which tempt him in his sleep:  and again to abnormal disturbances of sleep; in the two men, of whom one during the murder of Duncan laughed in his sleep, and the other raised a cry of murder; and in Lady Macbeth, who rises to re-enact in somnambulism those scenes the memory of which is pushing her on to madness or suicide.  All this has one effect, to excite supernatural alarm and, even more, a dread of the presence of evil not only in its recognised seat but all through and around our mysterious nature.  Perhaps there is no other work equal to Macbeth in the production of this effect.[197]