This author, not more to be admired for his intelligence than his candour, and who is entitled to praise for a higher degree of original thought than that to which he modestly pretends, relates a curious anecdote illustrating "the analogy between dreaming and spectral illusion, which he received from the gentleman to which it occurred,--an eminent medical friend:" "Having sat up late one evening, under considerable anxiety for one of his children, who was ill, he fell asleep in his chair, and had a frightful dream, in which the prominent figure was an immense baboon. He awoke with the fright, got up instantly, and walked to a table which was in the middle of the room. He was then quite awake, and quite conscious of the articles around him; but close by the wall in the end of the apartment he distinctly saw the baboon making the same grimaces which he had seen in his dreams; and this spectre continued visible for about half a minute." Now, a man who saw only a baboon would be quite ready to admit that it was but an optical illusion; but if, instead of a baboon, he had seen an intimate friend, and that friend, by some coincidence of time, had died about that date, he would be a very strong-minded man if he admitted for the mystery of seeing his friend the same natural solution which he would readily admit for seeing a baboon. [6] See Muller's observations on this phenomenon, "Physiology of the Senses," Baley's translation, p. 1395. [7] Sir David Brewster's Letters on Natural Magic, p. 39. [8] Newton's explanation is as follows: "This story I tell you to let you understand, that in the observation related by Mr. Boyle, the man's fancy probably concurred with the impression made by the sun's light to produce that phantasm of the sun which he constantly saw in bright objects, and so your question about the cause of this phantasm involves another about the power of the fancy, which I must confess is too hard a knot for me to untie. To place this effect in a constant motion is hard, because the sun ought then to appear perpetually. It seems rather to consist in a disposition of the sensorium to move the imagination strongly, and to be easily moved both by the imagination and by the light as often as bright objects are looked upon."--Letter from Sir I. Newton to Locke, Lord Kinq's Life of Locke, vol. i. pp. 405-408. Dr. Roget (Animal and Vegetable Physiology considered with reference to Natural Theology, "Bridgewater Treatise," pp. 524, 525) thus refers to this phenomenon, which he states "all of us may experience ":--