Optative

Collier's New Encyclopedia (1921)

in grammar, that form of the verb in which wish or desire is expressed, existing in the Greek and some other languages, its force being conveyed in English by such circumlocutions, as "may I," "would that he," etc. OPTICAL ILLUSION. An object appears large or small, near or distant, according as the rays from its opposite borders borders meeting at the eye form a a large l or a small angle; when the angle is large, the object is either large or near; when small, the object must be small or distant. Experience alone enables us to decide whether an object of large apparent size is so on account of its real size, or of its proximity; and our decision is arrived at by a comparison of the object in position with other common objects, such as trees, houses, etc. The same is, of course, true of apparently small objects. But when all means for comparison are removed our judgment is at fault. Similarly, we erroneously infer spherical solids at a distance to be flat disks, and a man in a white habit seems larger than he would if he wore a dark dress. Illusions are also produced by external causes. The persistence of impressions on the retina for about one-sixth of a second after the object which produced the impression has been removed produces another class of illusions. Common examples of this are the illuminated circle formed by the rapid revolution of an ignited carbon point, piece of red-hot iron, ron, or other luminous body. Another form of illusion is produced to a person who is seated in a vehicle in motion. The illusion is most complete when the attention is riveted on an object several yards off; this object then appears to be a center round which all the other objects revolve, those between the observer and the object moving backward, and those beyond the object moving forward. Other illusions arise from a disordered state of the organs of vision: e. g., the seeing of things double or movable, or of a color different from the true one.