304 



INDEX OF SUBJECTS 



Threshold, chromatic, 19, 60 



differential, 19, 30, 230, 233, 294 



general, 19, 60, 80, 117 



specific, 19, 60 

 Tone, 28 

 Total colour-blindness, 159, 186, 209, 217, 



267, 288 

 Trichromatic vision, 38, 158, 213, 274 



anomalous, 159, 182, 216, 235. 243, 266, 

 288 

 Trichromic, 294 

 Tritanopic vision, 159, 180, 233, 288 



Uniocular struggle, 275, 277 

 Unit of sensation, 20, 61 



Valency, 202, 253 



curves, 215 



white, 44, 202, 257, 264, 268 

 Variation, mean, 149 

 Vision of animals, 131, 196, 203, 298 



of primitive races, 131, 145 



anomalous trichromatic, 159, 182, 216, 

 235, 243, 266, 288 



deuteranopic, 159, 232, 287 



dichromatic, 158, 162, 216, 232, 267 



Vision, monochromatic, 159, 186, 217 

 288 



protanopic, 159, 232, 287 



recurrent, 85 



tritanopic, 159 180, 233, 288 



trichromatic, 38, 158, 213, 274 

 Visual acuity. 204 



method, 44, 99 

 Visual purple, 12, 196, 205, 212, 220, 292 



absorption by. 13, 205 



bleaching of, 13, 55, 206, 212 

 Visual substances. 12, 201, 219, 253, 270, 



271, 280, 285, 291 

 Visual yellow, 13, 197, 220 



Weber's law, 19 



White, 4, 25, 201, 202, 207, 211, 223, 226, 



283, 285 

 White valency, 44, 202, 257, 264, 268 



Yellow, 115, 198, 260, 283, 285, 298 

 Yellow spot, 9, 81 {see Fovea centralis) 

 Yellow, visual. 13, 197. 220 

 Young-Helmholtz theory, 199, 213 



Zones, theory of, 200 







