| FIGURE | | PAGE |
| [1.] | Principal parts of the eye | [14] |
| [2.] | Stereoscopic pictures for combining by converging or diverging the optical axes | [41] |
| [3.] | Stereoscopic pictures | [41] |
| [4.] | The vertical line appears longer than the equal horizontal line in each case | [46] |
| [5.] | The vertical dimension is equal to the horizontal one, but the former appears greater | [47] |
| [6.] | The divided or filled space on the left appears longer than the equal space on the right | [49] |
| [7.] | The three lines are of equal length | [50] |
| [8.] | The distance between the two circles on the left is equal to the distance between the outside edges of the two circles on the right | [50] |
| [9.] | Three squares of equal dimensions which appear different in area and dimension | [51] |
| [10.] | The vertical distance between the upper circle and the left-hand one of the group is equal to the overall length of the group of three circles | [52] |
| [11.] | Two equal semi-circles | [53] |
| [12.] | Arcs of the same circle | [53] |
| [13.] | Three incomplete but equal squares | [53] |
| [14.] | Middle sections of the two lines are equal | [54] |
| [15.] | An effect of contrasting areas (Baldwin’s figure) | [54] |
| [16.] | An illusion of contrast | [55] |
| [17.] | Equal circles which appear unequal due to contrast (Ebbinghaus’ figure) | [56] |
| [18.] | Equal circles appearing unequal owing to contrasting concentric circles | [56] |
| [19.] | Circles influenced by position within an angle | [57] |
| [20.] | Contrasting angles | [57] |
| [21.] | Owing to perspective the right angles appear oblique and vice versa | [58] |
| [22.] | Two equal diagonals which appear unequal | [58] |
| [23.] | Apparent variations in the distance between two parallel lines | [59] |
| [24.] | A striking illusion of perspective | [60] |
| [25.] | Distortion of a square due to superposed lines | [61] |
| [26.] | Distortion of a circle due to superposed lines | [62] |
| [27.] | Illustrating fluctuation of attention | [65] |
| [28.] | The grouping of the circles fluctuates | [66] |
| [29.] | Crossed lines which may be interpreted in two ways | [67] |
| [30.] | Reversible cubes | [68] |
| [31.] | The reversible “open book” (after Mach) | [69] |
| [32.] | A reversible tetrahedron | [69] |
| [33.] | Reversible perspective of a group of rings or of a tube | [70] |
| [34.] | Schröder’s reversible staircase | [70] |
| [35.] | Thiéry’s figure | [71] |
| [36.] | Illustrating certain influences upon the apparent direction of vision. |
| | By covering all but the eyes the latter appear to be drawn alike in both sketches | [73] |
| [37.] | Zöllner’s illusion of direction | [77] |
| [38.] | Parallel lines which do not appear so | [79] |
| [39.] | Wundt’s illusion of direction | [79] |
| [40.] | Hering’s illusion of direction | [80] |
| [41.] | Simple effect of angles | [81] |
| [42.] | The effect of two angles in tilting the horizontal lines | [83] |
| [43.] | The effect of crossed lines upon their respective apparent directions | [83] |
| [44.] | Another step toward the Zöllner illusion | [84] |
| [45.] | The two diagonals would meet on the left vertical line | [85] |
| [46.] | Poggendorff’s illusion. Which oblique line on the right is the prolongation of the oblique line on the left? | [85] |
| [47.] | A straight line appears to sag | [86] |
| [48.] | Distortions of contour due to contact with other contours | [87] |
| [49.] | An illusion of direction | [88] |
| [50.] | “Twisted-cord” illusion. These are straight cords | [89] |
| [51.] | “Twisted-cord” illusion. These are concentric circles | [89] |
| [52.] | A spiral when rotated appears to expand or contract, depending upon direction of rotation | [90] |
| [53.] | Angles affect the apparent length of lines | [91] |
| [54.] | The horizontal line appears to tilt downward toward the ends | [92] |
| [55.] | The horizontal line appears to sag in the middle | [92] |
| [56.] | The Müller-Lyer illusion | [93] |
| [57.] | Combined influence of angles and contrasting lengths | [95] |
| [58.] | Two equal oblique lines appear unequal because of their different positions | [95] |
| [59.] | An illusion of area | [96] |
| [60.] | Five equal areas showing the influence of contour upon judgment of area | [97] |
| [61.] | Showing the effect of directing the attention | [98] |
| [62.] | Simple apparatus for demonstrating the remarkable effects of contrasts in brightness and color | [115] |
| [63.] | Illustrating brightness-contrast | [117] |
| [64.] | An effect of brightness-contrast. Note the darkening of the intersections of the white strips | [118] |
| [65.] | The phenomenon of irradiation | [121] |
| [66.] | An excellent pattern for demonstrating color-contrast | [126] |
| [67.] | By rotating this Mason (black and white) disk color-sensations are produced | [133] |
| [68.] | For demonstrating retiring and advancing colors | [137] |
| [69.] | By combining these stereoscopically the effect of metallic lustre (similar to graphite in this case) is obtained | [141] |
| [70.] | A bas-relief lighted from above | [146] |
| [71.] | An intaglio lighted from above | [147] |
| [72.] | A bas-relief lighted from the left | [148] |
| [73.] | An intaglio lighted from the left | [149] |
| [74a.] | A disk (above) and a sphere (below) lighted from overhead | [145] |
| [b.] | A disk and a sphere lighted by perfectly diffused light | [145] |
| [75.] | A concave hemispherical cup on the left and a convex hemisphere on the right lighted by a light-source of large angle such as a window | [150] |
| [76.] | The same as Fig. 75, but lighted by a very small light-source | [151] |
| [77.] | Apparent ending of a searchlight beam | [161] |
| [78.] | An accurate tracing from a photograph (continual exposure) of the moon rising | [171] |
| [79.] | Accurate tracings from a photograph (short exposures at intervals) of the sun setting | [172] |
| [80.] | Explanation offered by Smith of the apparent enlargement of heavenly bodies near the horizon | [174] |
| [81.] | Explanation of a common mirage | [176] |
| [82.] | Illustrating the apparent distortion of a picture frame in which the grain of the wood is visible | [190] |
| [83.] | Another example similar to Fig. 82 | [191] |
| [84.] | From actual photographs of the end-grain of a board | [192] |
| [85.] | Exaggerated illusions in architecture | [198] |
| [86.] | Illustrating the influence of visual angle upon apparent vertical height | [199] |
| [87.] | Irradiation in architecture | [200] |
| [88.] | Some simple geometrical-optical illusions in architecture | [201] |
| [89.] | By decreasing the exposed length of shingles toward the top a greater apparent expanse is obtained | [202] |
| [90.] | An example of a mirror “illusion” | [207] |
| [91.] | Another example of “mirror magic” | [208] |
| [92.] | A primary stage in the evolution of the use of geometrical-optical illusions on ships | [226] |
| [93] and [94.] | Attempts at distortion of outline which preceded the adoption of geometrical-optical illusions | [228] |
| [95] and [96.] | Illustrating the use of models by the Navy Department in developing the geometrical-optical illusion for ships | [229] |
| [97] and [98.] | Examples of the geometrical-optical illusion as finally applied | [231] |
| [99.] | Representative earth backgrounds for an airplane (uncamouflaged) as viewed from above | [235] |
| [100.] | Illustrating the study of pattern for airplanes. The photograph was taken from an altitude of 10,000 feet. The insert shows the relative lengths (vertical scale) of an airplane of 50-foot spread at various distances below the observer | [239] |