Such a visionary duplicate of one’s-self—one’s fetch—is a not unfrequent form of sensorial illusion. In more ignorant days the appearance of a fetch excited much apprehension. It was supposed to menace death or serious calamity to its original. Properly viewed, unless it proceed from hard work and overstrained thought, (from which you can desist,) it indicates something wrong in your physical health, and its warning goes no further than to consult a doctor, to learn, “what rhubarb, senna, or what purgative drug will drive the spectre hence.” The efficiency of such means was shown in the case of Nicolai. Yet in this case, I may remark, the originating cause of the attack had been anxiety about the very son whose apparition was the first of the throng to visit him. Had the illusion continued limited to the figure of the son, it would have been more questionable what art could do towards dismissing it. At all events, in such a case, the first thing is to remove the perilous stuff that weighs upon the mind. So the personage whose words I have been using was doubtless right, in his own case, to “throw physic to the dogs.” In the tragedy of _Macbeth_, sensorial illusions are made to play their part with curious physiological correctness. The mind of Macbeth is worn by the conflict between ambition and duty. At last his better resolves give way; and his excited fancy projects before him the fetch of his own dagger, which marshals him the way that he shall go. The spectator is thus artistically prepared for the further working of the same infirmity in the apparition of Banquo, which, unseen by his guests, is visible only to the conscience-stricken murderer. With a scientific precision no less admirable, the partner of his guilt—_a woman_—is made to have attacks of trance, (_to which women are more liable than men_,) caused by her disturbed mind; and in her trance the exact physiological character of one form of that disorder is portrayed—_she enacts a dream_, which is the essence of somnambulism. One almost doubts whether Shakspeare was aware of the philosophic truth displayed in these master-strokes of his own art. The apparitions conjured up in the witch scenes of the same play, and the ghost in _Hamlet_, are moulded on the pattern of vulgar superstition. He employs indifferently the baser metal and the truthful inspirations of his own genius—realizing Shelley’s strange figure of “a poet hidden In the light of thought.”