Page:The New International Encyclopædia 1st ed. v. 20.djvu/228

VISION. 180 VISITATION. focused upon a definite point on the retina, thus indicating the point from which the light comes; consequently the size and shape of objects are judged by the size and shape of the retinal image. This estimation is aided by the muscular sense of the muscles moving the eyeball, a certain amount of action of these muscles being accom- panied by a certain degree of conscious effort. Our estimate of distance is to a great extent a jnatter of visual judgment, acquired as a result of experience, though it is also inlluenced bj' the size of the retinal image. A retinal image of given size may result from a distant object of large size or a small object near the eye; hence ■when we know the exact size of an object, we judge of its distance by the size of the retinal image; and. conversely, when we know the actual distance jit which an object is placed, we judge of its size by the size of its image on the retina. As a result of this relationship, if we err in regard to the size, we are led into error in our estimate of the distance. The Influence of Hextal Processes upox VisuAL Perceptions. Our estimate of the size, form, distance, and direction of objects is based largely upon previous experience, and is the re- sult of the physiological process of vision aided by former judgments which have been stored up in the brain. Such deductions are liable to error, either on account of error in judgment, or because of faulty vision. Vertical lines, for instance, ap- jiear longer than horizontal ones because we re- quire a more powerful contraction of the relatively weak upper straight muscle of the eye concerned in the required movement than is required of the comparatively strong muscles which move the eye laterally; we judge the upward motion of the eye to be greater because for an equal amount of motion we require a greater muscle impulse. A familiar example of this tendency to overestimate the vertical dimension is the conunon error of supposing the height of the crown of a silk hat to be greater than its breadth, an illusion which disappears when the hat is laid upon its side. Fio. 5, Zollner'8 Lines. Anexample of Illusion of apace perception. A striking example of illusion of space per- ception is afforded by ZJiUncr's lines, illustrated in Fig. .5. These lines appear to diverge and con- verge alternately, although really parallel to each other, owing to their ap[)arenf direction being changed to make them appear more nearly perpendicular to the oblique lines crossing them; this tendency for the eye to make acvite and ob- tuse angles approach right angles, is the result of our knowledge that images of familiar sur- rounding objects of square shape are often seen obliquely, and then form acute and obtuse angles upon the retina ; we thus acquire the habit of mentally correcting such visual impressions. See Illusion. Consult : Von Helmholtz, Handbuch der phpsiologisclien Optik (Leipzig, 1890) ; Le Conte, Sight (New York, 1807) ; Foster, Textbook of Physiology (ib., 1900) ; Kirkes, Handbook of Physiology (ib., 1902); Schaefer, Text- book of Physiology (Edinburgh and New York, 1900) ; American Textbook of Physiology (Phila- delphia, 1902) ; Graefe-Saemisch, Handbuch der gesaminten Augenheilkxinde (Leipzig, 1902) ; Xorris and Oliver. Systems of Diseases of the Eye (Philadelphia, 1900) ; May. Matiual of Dis- eases of the Eye (New York, 1904) ; Baldwin, Dictionary of Philosophy and Psychology (Xew Y'ork and London, 1901) ; Calkins, Introduction to Psychology (Xew York, 1901). VISION, Defects of. See Sight, Defects of. VISION OF DON KODERICK. A narra- tive poem liy Sir Walter Scott (1811) founded on a legend of the last Gothic King of Spain, written in aid of the Portuguese in the Penin- sular War. VISION OF JUDGMENT. A eulogy of George III. in English hexameters, by Robert Southey (1821). Its strongly accentuated con- servative prejudices excited much criticism from liberals, and it was burlesqued l)y Lord Byron in a ])oem bearing the same title (published in vol. i. of The Liberal, 182.3). VISION OF PIERS PLOWMAN. See Lang- land. William. VISION OF SIR LAUNFAL, The. A poem, partly allegorical, by .James Russell Lowell, published in 1848; founded on an Arthurian legend, and probably suggested by Tennyson's Sir Galahad. VISITATION, Sisters of the. A religious Order for women in the Roman Catholic Church, sometimes also known as Salesian Sisters, from Saint Francis de Sales, to whom the idea of its foundation was due. It was established in 1610 at Annecy, in Savoy, with the purpose of visiting and caring for the sick and needy. It took its name and its example from the visit paid to ■ Elizabeth, mother of .John the Baptist, by the Virgin Mary ( Luke i. 39-42 ) . The actual founder, under Saint Francis's direction, was Saint Jeanne Frances de Chantal (q.v. ). A second house was cst:il)lished in Lyons, but the archbishop of that see. Cardinal de Marquemont, desired Saint Francis to change his original plan of a con- gregation without regilar vows into a professed Order. This was accordingly done, with the adoption of the rule of Saint Augiistine. Pope Paul V. confirmed it in this form in 1(518. It spread through France and Italy, and now num- bers about 170 convents. In the I'nited States, to which it came in ISlfl. it has 22 convents and 700 sisters, whose principal occujiation is teach- ing. The devotion to the Sacred Heart of .Tesus, now so widespread in the Roman Catluilic Church, had its formal beginning in this Order, of which Margaret Mary Alacoque (q.v.) was a member.