506 DR WILLIAM PEDDIE ON A 



Mr A. at first said that he knew the difference between green and blue and that 

 he could distinguish them, but it was easy to prove to him that he could not do so. 

 When asked to name the colour, he was as often wrong as right. So that it is very 

 questionable if the statement " mixed with something " is of much value. 



Spectrum Matches. — Two patches of monochromatic light were looked at side by side. 

 While one was always yellow, the colour of the other was varied at pleasure. The intensity 

 of either could be altered until it was equal to that of the other. In this way Mr A. 

 matched with yellow, more or less darkened, all the colours yellow-green, green, blue- 

 green, blue, indigo, and violet, to the extreme end of the spectrum. I then, unknown to 

 Mr A., changed the yellow patch to dark red, and, making it almost invisibly dark, made 

 the other patch violet, and asked him to adjust them to equality. He at once said 

 that it was impossible to do so as the one was red. The same result happened when 

 the dark red patch was made a yellow-red and was darkened. He asserted that he 

 never saw red in spectrum violet. 



As in the previous observations, Mr A. said that he was thoroughly satisfied in 

 calling all the first-mentioned colours greys, with the exception of green and blue-green, 

 which he said made a somewhat unsatisfactory match with yellow, though I did not 

 find that the unsatisfactoriness was sufficient to enable him to distinguish green from 

 blue. Nevertheless I believe that it indicates that the green sensation is very nearly 

 appreciated. 



Superposition of Spectrum Colours. — The first and second columns contain the 

 names of the superposed colours, and the third column contains the name of the mixture. 

 The names used by Mr A. are in all cases given in brackets. 



Eed (red). Green (grey) Yellow (white). 



Eed (red). Blue (grey). Grey (grey). 



Yellow (white). Dark blue (grey). Grey (grey). 



Yellow-green (grey). Indigo (grey). Blue (grey). 



Green (grey). Violet (grey). Blue (grey). 



Comparison with the case described by v. Vintschgau and Heking. 



The experimental investigation of this case is given very fully by v. Vintschgau in 

 PJlilgers Arch. f. d. ges. Physiol., Bd. 48, s. 43, and Bd. 57, s. 191. Hering's discus- 

 sion is given in Bd. 57, s. 308 of that journal. There was great reduction in the intensity 

 of light from the normal value and the spectrum was much shortened at both ends. 

 Roughly speaking, red light began to be visible about half-way between the lines 

 C and D and vanished before D was reached. The spectrum was colourless from the 

 latter point until the yellow-green part was reached. This part was called " yellow." 

 The rest was called " green," up to a point slightly beyond F, then all colour again 

 vanished, and all light disappeared before the line G was reached. 



