Part 27

Size and distance, 35, 36 illusions of, 104, 166

Sky apparent form of, 166 brightness, 241

Skylight and sunlight, relative proportions of, 215, 243

Smith, Robert, 173

Smoke-screens, 230

Spectral character of light, 189

Sphere, illusions, 145, 150, 151

Spherical aberration, 19

Sphinx illusion, 206

Spiral illusions, 90

Spraying, paint, 187

Stereoscope, 39, 142

Stereoscopic vision, 38, 41, 141

Submarines, 225 camouflage for, 232

Sun, apparent enlargement at horizon, 169

Sunlight and skylight, relative proportions in nature, 215, 243

Terrestrial camouflage, 210

Theory of influence of angles, 98 perspective, 98 dynamic, 99 confusion, 100 indirect vision, 100 mean distance, 101

Thiéry's figure, 71

Thiéry's perspective theory, 99

Transparencies, 185

Twisted cord illusions, 88

Uibe, 167

Vertical vs. horizontal distances, 11, 36, 46

Visibility, low, for vessels, 222 of airplanes, 233

Vision, 29 persistence of, 131 stereoscopic, 38

Visual perception, 32, 33

Warm and cold colors, 158