Seeking for an explanation Mr. Frazer gives a thoroughly modern doctrine of visual and auditory hallucinations, as revived impressions of sense. The impressions, 'laid up in the brain, will be reversed back to the retiform coat and crystalline humour,' hence 'a lively seeing, as if, de novo, the object had been placed before the eye'. He illustrates this by experiments in after-images. He will not deny, however, that angels, good or bad, may intentionally cause the revival of impressions, and so, for their own purposes, produce the hallucinations from within. The coincidence of the hallucination with future events may arise from the fore-knowledge of the said angels, who, if evil, are deceptive, like Ahab's false prophets. The angel then, who, through one channel or another, fore-knows, or anticipates an event, 'has no more to do than to reverse the species of these things from a man's brain to the organ of the eye'. Substitute telepathy, the effect produced by a distant mind, for angels, and we have here the very theory of some modern inquirers. Mr. Frazer thinks it unlikely that _bad_ angels delude 'several men that I have known to be of considerable sense, and pious and good conversation'. He will not hear of angels making bodies of 'compressed air' (an old mystic idea), which they place before men's eyes. His own hypothesis is more economical of marvel. He has not observed second sight to be hereditary. If asked why it is confined to ignorant islanders, he denies the fact. It is as common elsewhere, but is concealed, for fear of ridicule and odium. He admits that credulity and ignorance give opportunities to evil spirits 'to juggle more frequently than otherwise they would have done'. So he 'humbly submits himself to the judgment of his betters'. Setting aside the hypothesis of angels, Mr. Frazer makes only one mistake, he does not give instantiae contradictoriae, where the hallucination existed without the fulfilment. He shows a good deal of reading, and a liking for Sir Thomas Browne. The difference between him and his contemporary, Mr. Kirk, is as great as that between Herodotus and Thucydides.