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ILLUSION. A species of mania in which the sensibility of the nervous system is altered, excited, weakened or perverted. The patient is deceived by the false appearance of things, and his reason is not sufficiently active and powerful to correct the error, and this last particular is what distinguishes the sane from the insane. Illusions are not unfrequent in a state of health, but reason corrects the errors and dissipates them. A square tower seen from a distance may appear round, but on approaching it, the error is corrected. A distant mountain may be taken for a cloud, but as we approach, we discover the truth. To a person in the cabin of a vessel under sail, the shore appears to move; but reflection and a closer examination soon destroy this illusion. An insane individual is mistaken on the qualities, connexions, and causes of the impressions he actually receives, and he forms wrong judgments as to his internal and external sensations; and his reason does not correct the error. 1 Beck's Med. Jur. 538; Esquirol, Maladies Mentales, prem. partie, III., tome 1, p. 202. Dict. des Sciences Medicales, Hallucination, tome 20, p. 64. See Hallucination.

A Law Dictionary, Adapted to the Constitution and Laws of the United States. By John Bouvier. Published 1856.
References in periodicals archive ?
"I drew this optical illusion in Adobe Illustrator on September 26, 2016.
These stars have also pursued that spellbinding hourglass shape, but their optical illusion figure-fixing dresses didn't work their magic on them all...
Through the interactive museum, visitors can share some laughter as they entertain their eyes and learn how the brain works as they go into different rooms of optical illusions and sensory games.
OREGON -- In a bizarre incident, the Newport Police in Oregon, United States was informed about a 'gangster cat' sitting in a tree which later turned out to be an optical illusion.
Chidambaram over his claims that the Congress has emerged as the winner in Gujarat, saying the Finance Minister is suffering from an optical illusion.
Brian Wilton and wife Isobel captured the optical illusion as the setting sun threw an eerie light into a dense almondshaped cloud.
Thunder Bay was to have been his representative in the sprint handicap, but routine identity checks made at the racecourse revealed the horse he sent to the races was, in fact, Optical Illusion.
Students enjoyed the challenge of creating an optical illusion. This project only took two days to complete, and it is also great if there is a limited budget.
Close to the horizon, the moon will appear bigger than usual - an optical illusion caused by the proximity of trees and buildings.
Students at this age are also fascinated with the idea of optical illusion. Whether through a Magic Eye book, psychedelic picture, or a kaleidoscope, they have been exposed in one way or another to the illusionist idea.
THE dictionary definition of mirage is 'an optical illusion caused by atmospheric conditions' - which explains a lot about a night out I had at a bar of the same name recently.