| 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 |
| 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 |
| 93and94. | Attempts at distortion of outline which preceded the adoption of geometrical-optical illusions | 228 |
| 95and96. | Illustrating the use of models by the Navy Department in developing the geometrical-optical illusion for ships | 229 |
| 97and98. | 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 |
