=ABERRA′TION.= [Eng., Fr.] _Syn._ ABERRA′TIO, L. A wandering or deviation from the usual course, or from the normal condition. In _optics_, the deviation of the rays of light from the true focus, when inflected by a lens or speculum. This arises from a difference in the physical nature of the rays, from the figure of the lenses or specula, or from the nature of the materials of which the media traversed are composed. See ACHROMATISM, LENS, &c. =Aberration of mind.= Mental alienation or wandering; insanity. A term frequently applied, in familiar language, to a mild form of incipient insanity or dementia, which is more or less occasional or continued, trifling or severe, according to circumstances. The studious, nervous, slothful, and those who are engaged in sedentary occupations and spend much of their time in ill-ventilated apartments, or who indulge in irregular or vicious habits, as well as ‘fast livers,’ are the most liable to this affection. It also frequently arises from disordered physical health. _Treat., &c._ Change of scene, out-door exercise, agreeable company, pleasing and continued mental occupation, and due attention to diet, clothing, ventilation, &c., with the judicious use of some mild aperient medicine and tepid bathing, will generally alleviate, and frequently effect a cure. For the prevention of its accession, or its recurrence, care should be taken to promote the general health, and also, where necessary, to elevate the spirits and to divert the mind. =ABLU′TION.= [Eng., Fr.] _Syn._ ABLU′TIO, L. In a _general sense_, washing, cleansing, or purification by water.