THE SENSE OF VISION 



627 



appear green. Yet it is astonishing with what accuracy such a person 

 can learn to name and match colours. He does not see the lips and 

 cheeks as red, but learns to call them so. One case of colour-blindness 



FIG. 350. THE EDIUDGE-GREEN COLOUR PERCEPTION LANTERX. 



The lantern consists of four discs: three carrying seven coloured glasses Clear, 

 red A, red B, yellow, green, signal green, blue, purple and one carrying seven 

 modifying glasses Clear, ground glass, ribbed glass, and five neutral glasses. 

 Each disc has a clear aperture. The diaphragm is graduated in respect to three 

 apertures to represent a 5-inch railway signal bull's-eye at 600, 800, and 1,000 

 yards respectively when the test is made at 20 feet. The colours are brought 

 successively into view by moving one or more of the handles to position, denoting 

 the colour or modifier in use, on the scale at the top of the lantern. The classi- 

 fication of colour perception is as follows: 



Heptachroinic appreciating in 



the spectrum . . . . Red Orange Yellow Green Blue Indigo Violet 

 Hfxachromic appreciating in 



the spectrum . . ' . . Red Orango Yellow Grc\-n Blue 

 Pentachromic appreciating i.n 



the spectrum .. .. Red , Yellow Green Blue 

 Tetrachromic appreciating in 



the spectrum . . . . Red Yellow Green 



Trichromic appreciating in 



the spectrum . . . . Red 

 Dichromic appreciating in the 



spectrum . . . . . . Red 



Totally colour-blind appreciating Light and Shade only 



Violet 

 Violet 

 Violet 

 Violet 

 Violet 



explained that all colours appeared modifications of blue and yellow. 

 The brightest and purest yellow he called yellow; a slightly darker 

 and not so pure a yellow was green to him. A darker yellow still 



