Hallucination may be roughly defined as false sense impression. For example, the patient sees an object which has no real existence, or hears an imaginary voice. Hallucinations are termed visual, auditory, tactile, _etc._ according to the sense to which the false impression appears to belong.[42] Hallucination is induced by the unusual suggesting the expected. It is sense-perception colored by association. It is the power of a dominant idea that, unbidden, enters the field of consciousness and takes possession of even the senses themselves. In Halifax one idea seemed to dominate most minds and clothe itself in the semblance of reality--the expected Germans. For a long time there had been under public discussion the question as to whether or not the city would be shelled by Zeppelin raiders, or possibly by a fleet at sea. All street-lights had been darkened by military orders. The failure to draw window shades had been subject to heavy penalty. It is no wonder eyes looked upward when there came the crash, and when seeing the strange unusual cloud beheld the Zeppelin of fancy. A man residing on the outskirts of the town of Dartmouth "heard" a German shell pass shrieking above him. Dartmouth Heights looks out over Halifax harbor, and here perhaps the vista is most expansive, and the eye sees furthest. The instant after the explosion a citizen standing here "saw" clearly a German fleet manoeuvering in the distance.[43] That shells had actually come few on the instant doubted. The head of one firm advised his employees not to run elsewhere, as "two shots never fall in the same place." [42] Hart, Bernard, _The Psychology of Insanity_ (Cambridge, 1916), ch. iii, p. 30. [43] "So hypochondriac fancies represent Ships, armies, battles in the firmament Till steady eyes the exhalations solve And all to its first matter, cloud, resolve." --Defoe, _Journal of the Plague Year_. This--a German assault--was the great mental explanation that came into the majority of minds. There was one other--that of the end of the world. Many fell to their knees in prayer. One woman was found in the open yard by her broken home repeating the general confession of the church. Few would have been surprised if out of the smoky cloud-ridden skies there should have appeared the archangels announcing the consummation of mundane affairs. Indeed there were instances, not a few, of those who "saw" in the death-cloud "the clear outlines of a face." Thus both auditory and visual hallucination were manifested to a degree.