HELMHOLTZ IN KONIGSBERG 



(3.) Green excites strongly the green, feebly the 



other two sensation, green. 



(4.) Blue excites moderately the fibres sensitive to 

 green and violet, and feebly the red sen- 

 sation, blue. 



(5.) Violet excites strongly the fibres sensitive to 

 violet, and feebly the other two sensation, 

 violet. 



(6.) When the excitation is nearly equal for the 

 three kinds of fibres, then the sensation is 

 white. 



Another mode of expressing the theory is to say 

 that each primary sensation of red, green and violet 

 is excited in some degree by almost every ray of the 

 spectrum, but the maxima of excitation occur at 

 different places, while the strength of stimulation in 

 each case diminishes in both directions from the 

 maximum point. Thus when the three sensations 

 are equally excited, white light is the result ; green 

 is caused by a very weak violet stimulation, a stronger 

 red, and a still stronger green stimulation. At each 

 end of the spectrum we have only the simple sensa- 

 tions of red and violet, and all the intermediate colour 

 sensations are compounds of varying proportions of 

 the three primaries. 



According to this theory, red blindness is attribut- 

 able to the absence of the red sensation, and green 

 blindness to the absence of the green sensation. 

 When the green and violet sensations are equal in 

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