Frequency of illusions - Opinions relative to the errors of the senses - Characteristics by which illusions and hallucinations are distinguished - Opinions of MM. Calmeil, Aubanel, and Deohambre; their concurrence - Peculiar characteristics of illusions - Internal hallucinations allied with sensations of hypochondriacs - Illusions are observed both in a healthy and a morbid state - Illusions of hearing and of sight - Causes - Illusions of sight sometimes epidemic - Aerial illusions - Causes of public illusions - Illusions of hearing - Motives for the chapter - Illusions may precede, accompany, or succeed hallucinations - Illusions may be isolated or general - Illusions very capricious - Illusions, like hallucinations, may induce the commission of reprehensible acts - Illusions of the touch, of the smell, of the taste - Their influence on the conduct of madmen - Illusions almost always accompany hallucinations - Recapitulation.

Nothing is more common with the insane, and especially with maniacs, than to mistake one person for another, and to take an object for what it is not. Such mistakes are frequent; so that the story of a windmill metamorphosed into a giant is a tale appropriate for all times. These errors of the senses are not confined to the deranged. They exist equally among men of the most healthy minds; but judgment and experience correct their false notions. In the eighteenth century, it was established in the schools of philosophy that our senses deceive us, and that we cannot place any reliance upon them.

It requires, however, but little reflection to convince us that the senses faithfully report all that makes an impression on them. Their office is to tell us that there exists such and such a cause in the body, such or such a. quality that produces in us such or such a sensation, but not to tell us the nature of that cause or that quality. Thus the only proper object of sight is the colored expanse. In seeking to arrive at a knowledge of the form and distance of objects,* we form a conjectural judgment. This judgment, in itself, no more forms a part of the evidence of the sense of sight, than the judgments which we form relative to sounds that the ear hears, and in relation to the nature and distance of sonorous bodies whence those sounds emanate, form a part of the testimony of the sense of hearing. Thus, to speak correctly, our senses never deceive us; but we deceive ourselves through the judgments we form concerning the testimony of our senses.

When Esquirol published his Memoires sur let Illusions, he pointed out wherein illusions differ from hallucinations. The characteristic, which appears to us the most decisive, is the absence of an exterior body in hallucinations; whilst illusions require a tangible basis. A man declares that you are a cat, or Napoleon, or a well-known orator; he sees fighting armies in the clouds - angels who blow the trumpet; that man is a visionary. But if, in the quiet of night, he hears voices addressing him; if, in the most intense darkness, he sees persons that none but himself can perceive, he is hallucinated. The privation of the sense of sight or hearing presents no impediment to hallucination, whilst it is an obstacle to illusion.

M. Dechambre does not consider that any argument has been adduced sufficiently conclusive to justify Esquirol's distinction between hallucinations and illusions. He says that the halluci-nist who hears a voice speaking to him, and the visionary who thinks the friend standing before him is an ox or a horned devil, belong to the same category. With the one, as with the other, the brain is diseased - not the organ of sight or hearing, †

There is no doubt that the lesion that produces these two morbid phenomena exists in the brain; but it may be said that their progress is inverse - for, whilst hallucination seems to start from the nerve to form an outward image, illusion follows a directly contrary course; so that the one may be said to be subjective, the other objective.

Observation, it is true, points out the fact that illusions frequently coexist with hallucinations; that the two become blended; and that it is often difficult to distinguish them; but all these arguments have been produced against the present classification of the forms of madness; yet there is no author who does not acknowledge the necessity of describing them separately. In view of these considerations, and especially the existence of an object in illusions, we have persisted in considering the two phenomena as distinct; notwithstanding the contrary opinion is held by very competent men, Messrs. Calmeil, Aubanel, and several others. Moreover, in the two cases, the psychological phenomena appear to us to differ; and in regard both to their prognosis and treatment, we think, with M. Michla, that hallucinations should be distinguished from illusions. For similar reasons, we connect with illusions all those false sensations which proceed from the disease of an internal organ, as the stomach, the intestines, etc, and all the sensations peculiar to hypochondriacs, whose hallucinations depend on some internal derangement.

* CEuvres philosophique do P. Buffier, avec les notes par M. Francisque Boullier, introduction, p. 53, Paris, 1843: Coll. charpentier. † Gaz. Med., April 6, 1850: Analyze De l'ouvrage de M. Szafkowski.

Illusions occur frequently in a healthy condition; they are easily corrected by reason. It is needless to repeat the examples so often cited in which a square tower appears round - in which the shore appears to recede. These facts have long been properly appreciated: but there are illusions which the progress of science has only lately developed; such as the giant of the Brocken, the fairy Morgana, and the Mirage.

At certain times, the giant was seen on the summit of the Brocken (one of the Hartz Mountains), to the great astonishment of the inhabitants and travellers. For many years, this prodigy had given occasion to the most wonderful tales, when Mr. Haue had the curiosity to examine into the cause, which he was fortunate enough to discover. Whilst gazing on the giant, a violent gust of wind almost carried away his hat; he quickly raised his hand, and the giant likewise raised his hand; he bowed, and his bow was returned. Mr. Haue summoned the master of the inn at the Brocken to witness his discovery. The experiment was repeated with similar results. The wonder was then explained. It was nothing but the effect of light produced by an object highly illuminated and surrounded by light clouds, which object, being reflected at a greater or less distance, was extended by an optical illusion to the height of five or six hundred feet.*

* Philosophical Magazine, vol. i. p. 232.

The interesting little work by Brewster, which we have already mentioned, may be consulted on this subject. A similar illusion has been noticed in Westmoreland, and other mountainous countries, where troops of cavaliers and armies appeared to be marching and countermarching, though they were, in fact, only the reflection of horses grazing on an opposite hill, or of peaceable travellers.

Many circumstances may give rise to illusions. Ignorance chiefly induces them. Certain countries, several provinces in France, and many estates, abound with traditions which have arisen from illusions of sight.

A vivid impression, the recollection of an event that has caused great excitement, may, through an association of ideas, give rise to an illusion.

"I was in Paris," says M. Wigan, "at a soiree given by M. Bellart, some days after the execution of the Prince of Moskowa. The usher, hearing the name of M. Marechal aine (the elder), announced M. le Marlchal Ney. An electric shudder ran through the assembly, and, for my part, I own that the resemblance to the prince was for a moment as perfect to my eyes as reality."*

Fear, remorse, and obscurity are very favorable to illusions. To these various causes may be traced apparitions linked with some object, such as the folds of a drapery, or a curtain, or those occasioned by the situation of a piece of furniture, when combined with the effect of a pale or doubtful light.

When the mind is thus prepared, the most familiar objects are transformed into phantoms. Ellis relates an anecdote of this kind that happened to the captain of a vessel at Newcastle-on-Tyne, and which he heard from an eye-witness.