Page:The New International Encyclopædia 1st ed. v. 07.djvu/658

* FIGURE. 600 FIGUREHEAD. filled equilateral triangle with sides 4.3 mm. in length. The largest stimuli used: angle 10 mm., open circle 11 mm., filled circle 12 mm., and triangle 9 mm., were too small to be cognized on the forehead, cheek, ball of thumb, and volar side of the wrist. This dependency of the form-limen upon the place stimulated is illustrated by the simple experiment of drawing a pair of dividers along the arm from the elbow to the finger-tips, or from the lobe of one ear to the lobe of the other, across the face. The objectively parallel lines seem to diverge toward the wrist, and as they pass the lips. The cutaneous limen for form is susceptible of marked decrease through prac- tice, as is well shown in the ability of the blind to read by touch from raised letters or from raised points of varied number and arrangement. The visual perception of figure may, like the perception of simple extension, be obtained by the resting eye in monocular vision, but for its full development binocular vision is essential. The visual perception of figure furthermore in- volves not only the perception of surface, but the perception of depth, or the apprehension of extension in the third dimension. One prob- lem of the perception of surface consists in recon- ciling the fact that the field of vision pre- sents a continuous surface with the fact that the sensitive parts of the retina, the rods and cones, form a mosaic of discrete points separated by non-sensitive areas. (The diameter of a ret- inal cone is estimated at 0.0015-0.0044 mm., and the distance from the centre of one cone to the centres of adjacent cones at 0.0040 mm.) While explanations have been made in terms of binocu- lar vision, of eye-movement, and of our a priori bias toward continuity. Kuelpe asserts that there is no real problem here at all. See also Blind Spot. Of special importance to the perception of the third dimension of figures are those optical phenomena known as the prevalence and rivalry of contours. When we observe the form of an object, the images which are cast upon the retinas of the two eyes differ slightly, owing to the difference in the position from which the two eyes view the object. If now those two images completely fused, the principal factor in the perception of depth would be removed; if. on the other hand, the two images remained obstinately disparate, it would be impossible to refer them to a single external object. It is the 'prevalence' and 'rivalry' of contours which "prevent the fusion of the two retinal images, and secure to < ach a certain amountof independence" ( lb-ring) ; although "the impressions 'if the two eyes always fuse to a single idea" (Wundt). The contour phe- nomena are easily demonstrable with the aid "f the stereoscope. If. e.g. the right eye hi- stimu- lated by a uniform surface of while ami (lie left eve by a black letter A upon a while background, there is afforded a pure instance of the prevalence of contour. The A is not made grayish, not washed over by the white of the right monocular field, hot is seen in perfect clearness in the re- sultant single field: iis contour suppresses or prevails over the surf presented by the white field, [f each retinal field contains contours, ami "le' in i" ess little congruence, the phe ' ■hum of 'rivalry of contours' is observed. is, if the letter 1" were presented to the left e * and W to the right, or a vertical black hand to the 'ell eye, ami a horizontal black band to the right, there would be no fusion of thi twa images, nor would either image permanently pre- vail over the other; but there will be a constant rivalry and alternation of the two fields. The visual perception of form plays an im- portant part in the production of what are known as the "elementary aesthetic feelings." I See .Esthetics, Experimental. ) Finally, tin- per- ception of figure is extremely subject to illusion; small angles are overestimated, the height of a square is overestimated, etc. (See article Il- lusion.) Consult: Titcbener, Experimental Psychology (New York, 1901); Wundt, Human and Animal Psychology (Eng. trans. London, 1896) ; Kuelpe, Outlines of Psychology (London, 1895). FIGURED BASS, or THOROUGHBASS. A system of musical notation in which winds are denoted by placing figures over the bass note. It was first used in Italy during the latter part of the sixteenth century. The original object was to furnish the organist with a simple means of recognizing at a glance the necessary harmonic foundations in large choral or instrumental works. (The arrangement of the different parts in a score (q.v. ) was not known then.) Playing from figured bass was a great art. because this system of notation indicates only the chord or its inversions, but nothing as to the leading of the various voices. To-day the art is not called for, as modern scores are written out in detail, and the figured bass in scores of the older masters (Bach, Handel) has been written out by eminent masters. (See Franz.) Figured bass plays an im- ■ rr*^ F— I H -= — 3"- r~^ ~W A PpUfc i 6 "*^T 1 6 4 CO 6 — S* — 6 9 7 — » pl- ' 1 6 4 7 — <& — — o— ^ — Cl-^ portant part in the study of harmony, as all ex- ercises are written in figured bass notation. Only thebass note is written. If no figure appears above the note, the ordinary triad is meant; the figure 6 denotes the first, J the second inversion. The dominant seventh is expressed by 7; its inver- sions by 4, ', 2 respectively. Suspensions are expressed h two figures, the first indicating the dissonance, the second its resolution. The in terval of the third is not written out unless chro- matically altered. Chromatic alterations are denoted by the usual signs placed before or after the liijiire 3jf, 5b. 61;. Sharps are also indicated by a line through the figure, S. In figured bass all intervals arc counted from the bass note, not the fundamental (q. v.). For further information or complete exposition of the theory of figured bass, consult Richter, Manual of Harmon!/, trans latcd by Morgan (London, 1880). FIGUREHEAD. A figure, or image, either a head, or bust, or full length, usually carved from wood, but in some recent vessels of hollow- east bronze, carried at the prow or stem of ships. Its form is frequently dependent upon the name of the ship; the United States ship Delawan had the head of an Indian, supposedly of the Dela- ware tribe; the Macedonian had the bust of a M: (Ionian warrior. <■! r-. 'the custom of placing figureheads on vessels of war is very ancient | the Phoenicians, Egyptians, Greeks, Romans, and