That such hallucinations have no real existence as far as the eye goes, is proved by the fact of many people who have lost their sight, being subject to them. It is hardly to be wondered at that those who by accident have been deprived of their sight, should wish so ardently to see once more the persons and sights they have taken pleasure in, that they should at last create for themselves illusions of this character. The same thing has frequently occurred with those whose sight is more or less weak. An old man of eighty, who was purblind, never sat down to a table during the last years of his life, without seeing around him a number of his friends who had long been dead, dressed in the costume of fifty years before. This old man had but one eye, which was extremely weak, and wore a pair of green preservers, in the glass of which he continually saw his own face reflected. Doctor Dewar, of Stirling, mentioned to Abercromby a very remarkable instance of this species of hallucination. The patient, who was quite blind, never walked in the street without seeing a little old woman hobbling on before him and leaning on a stick. This apparition always disappeared when he entered his house. Similar illusions frequently happen to every one, even the most healthy amongst us, but a little consideration soon puts them to flight. It would be useless to mention the numberless cases in which a square tower has appeared round, or where the landscape has suddenly seemed to recede from the sight. Such illusions as these have been long well known, and appreciated at their proper value; but there are others whose true cause has remained a mystery, until explained by the progress of science, such as the Spectre of the Brocken, the Fata Morgana, and the mirage. Analogous appearances have been seen in Westmoreland and other mountainous districts, the inhabitants imagining that the air was full of troops of cavalry, and whole armies even; such illusions resulting simply from the shadows of men and horses passing over an opposite mountain being thrown on the fog. A vast number of different circumstances give rise to these illusions, such as a strong impression, or the recollection of some striking event, which may easily cause them, by the association of ideas. Wigan relates, that being at a _soirée_ held at the house of M. Bellart, a few days after the execution of Marshal Ney, the groom of the chamber, instead of calling out the name of _M. Maréchal aîné_ (M. Maréchal, senior), announced the arrival of M. le Maréchal Ney. A shudder passed through the company, and many of them declared, that for an instant they saw the face and figure of the dead man in place of those of his involuntary representative.