VISIBLE SPEECH 236 VISION VISIBLE SPEECH, the system of ex- pressing speech sounds by written sym- bols, invented by Prof. Alexander Mel- ville Bell during the years 1849-1864. Its fundamental principle is, says its author, "that all relations of sound are symbol- ized by relations of form, each organ and each mode of organic action having its appropriate symbol, and all sounds of the same nature produced at different parts of the mouth (such as t and d, b and p) being represented by a single sym- bol turned in a direction corresponding to the organic position." The shapes of these symbols not being founded on any existing alphabet, the system here can only be illustrated, in the absence of the peculiar fount, by two that bear an acci- dental likeness to our current letters — O, symbolizing that the throat is open, and C, that part of the mouth is contracted. Among the advantages claimed for vis- ible speech by Professor Bell are its pow- er of representing the exact sounds of foreign languages (even Zulu clicks), and the facilities offered by it toward teaching the illiterate and blind to read, and the deaf and dumb to speak. But though the first at least of these claims has been established by rigid tests, and is admitted by A. J. Ellis and other emi- nent phonologists, the system has not, as its inventor hoped, been taken up by the government. See Bell's "Visible Speech," "The Science of Universal Al- phabetics" (London, 1867). VISIGOTHS, the Western Goths, who came from Scandinavia, and settled in Mcesia, a. d. 376. They established them- selves in Gaul A. D. 412, and, passing into Spain, founded a kingdom there in 414, which was overthrown by the Moors in 712. The names of the kings were: Ataulfus to 414 Wallia 415-418 Theodores. .... 418- ? Theudis 531-548 Theudlsele o48-550 Agila (at Merl- da) 550-554 Atharaglld. . . . 556-567 (Toledo his capital) Liuva (at Nai bonne) 567-568 Leovigild 568-586 Rocared 586-601 Liuva II 601-603 Vitteric ,603-610 Gundemar 610-612 Sisebut 612-620 Recared II 620-621 Suintella 621-631 Sisenand 631-636 Tulca 636-642 Chlndasvindg. . 642-649 Recesvinde. . . . 649-672 Wamba 672-680 Ervige 680-687 Egiza 687-701 Wltiza 701-710 Roderic 710-711 VISION, the act of seeing, that faculty of the mind by means of which, through its appropriate material organ, the eye, we perceive the visible appearances of the external world. Vision is mainly concerned with the color, form, distance, and tridimensional extension of objects. It is caused by impact of ether waves on the retina of the eye, but if these waves be longer or shorter than a certain limit, there is no visual impression produced by them. The apparent color of an ob- ject depends partly on the wave length or wave lengths of the incident light waves, single or mixed, and partly on the state of the eye itself, as in color blindness, or after taking santonine, which makes external objects look yellow, or in jaun- dice. The apparent brightness of an ob- ject depends on the amplitude of the light waves which pass from it to the eye; and the smallest perceptible difference of brightness always bears a nearly con- stant ratio to the full intensity of the bright objects (Fechner's psychophysi- cal law) . As between different colors the eye perceives them with different inten- sities, even when the physical intensity is the same; thus yellow appears brighter in a bright light than an equally intense red; and as light fades away the differ- ent colors fade away unequally, so that the ratio in Fechner's law is different for each color; red and yellow disap- pear first, blue last; and thus in a dim light the blue is the brightest. The leading problems in the theory of vision are, however, those which deal with the nature of our perception of dis- tance and of three-dimensional extension. According to Bishop Berkeley, whose views ("On the Theory of Vision") have met with the widest acceptance, we do not by means of sight perceive either that external objects are outside our- selves or their distance from us; but this knowledge is derived from touch and from our experience of motion from place to place; and as our experience is in general uniform, we come to associate the visible with the tangible so readily that we fancy we directly see visible ob- jects. As regards the distance of any given point, Berkeley maintains that this cannot be seen, "for distance being a line directed endwise to the eye, it projects only one point in the fund of the eye; which point remains invariably the same, whether the distance be longer or short- er." This may be true, and yet the eye may be obliged to put forth perceptibly different efforts in order to discriminate points situated at different distances. Rays proceeding from the distant point form a cone, whose base is the pupil of the eye; and in order to make this di- vergent cone converge on a point in the retina a distinct effort of focussing or accommodation is necessary for each dis- tance. That the distance may be judged by means of the necessary effort of ac- commodation may be seen by taking a small thin-edged lens, holding it at arm's length, and viewing distant objects through it. A small inverted image of the distant objects is seen; but on try- ing to ascertain at what distance this
