Visions, that is, the perception of apparently tangible objects in the outer world, which only exist in our imagination, have been known from time immemorial among all nations on earth. They are, in themselves, perfectly natural, and can frequently be traced back without difficulty to bodily affections or a disordered state of the mind, so that many eminent physicians dispose of them curtly as mere incidental symptoms of congestion or neuralgia. They may present real men and things, known beforehand, and now reproduced in such a manner as to appear objectively; or they may be ideal forms, the product of the moment, and incompatible with the laws of actual life. Persons who have visions and know nothing of their true nature, are apt to become intensely excited, as if they had been transferred into another world. The images they behold seem to them of supernatural origin, and may inspire them with lofty thoughts and noble impulses, but only too frequently they disturb their peace of mind and lead them to crime or despair. When visions extend to other senses besides sight, and the peculiar state of mind by which they are caused affects different parts of the body at once, they are called hallucinations; most frequent among insane people, of whom, according to Esquirol, eighty in a hundred are thus affected, they are generally quite insignificant; while visions through the eye, are often accompanied by very remarkable magic phenomena. Thus the visions which great men like Cromwell and Descartes, Byron or Goethe, record of their own experience, were evidently signs of the great energy of their mental life, while in others they are as clearly symptoms of disease. Ascribed by the ancients to divine influence, Christianity has invariably denounced them--when not indubitably inspired by God, as in the case of the martyr Stephen and the apostle St. John--as works of the Devil. At all times they have been communicated to others, either by contagion or, in rare cases, by the imposition of hands, as they have been artificially produced. Thus extreme bodily fatigue and utter prostration after long illness are apt to cause hallucinations. Albert Smith, for instance, while ascending Mont Blanc, and feeling utterly exhausted, saw all his surroundings clearly with his eyes, and yet, at the same time, beheld marvelous things with the so-called inner sense. A Swiss who, in 1848, during a severe cold, crossed from Wallis to Kandersteg by the famous Gemmi Pass, eight thousand feet high, saw on his way a number of men shoveling the snow from his path, fellow-travelers climbing up on all sides, and rolling masses of snow which changed into dogs; he heard the blows of axes and the laughing and singing of distant shepherds, while his road was utterly deserted, and not a human soul within many miles. His hands and feet were found frozen when he arrived at last at his quarters for the night, and ten days later he died from the effects of his exposure.