1891.] 



Colour of Gates of lobacco Scotoma, fyc. 



497 



the direction BL, always falls on E, at the end of which a paper disc 

 can be placed. A mirror without this arrangement can be employed, 

 the light falling on a paper strip, but is not quite so convenient. The 

 monochromatic light was thrown on the micro r, and the angular 

 deviation from the zero point read, the eye being fixed on a point 

 along the zero reading. The experiments were made first with the 

 ordinary luminosity of colours, and subsequently with the reduced. 



Scale No. Wave length. Temp. side. Nasal side. 



56 

 52 

 47 

 56 

 52 

 47 

 23 



6330 

 5996 

 5658 

 5330 

 5996 



14 



14 



15 



14 



14 



side. 



5658 white all over the field 

 4600 sees blue throughout. 



10 1 



in L Square patch, 2-inch 



11 



10 



10 [ Small round, spot, 

 ^-inch diam. 



In the above, the angles show where colour was first visible. 



Case II. The next two subjects are brothers (Alfred and William 

 P., indicated below as P and Q), whose colour perception is mono- 

 chromatic. Mr. Nettleship had previously tested them with wools, 

 and the matches they made, such as matching yellow with blue, 

 made it evident that their colour vision was very abnormal. The 

 defect is not due to active disease, but they were born with it. 

 They suffer from amblyopia. These cases were published as cases 

 of " Day-blindness with Colour-blindness," by Mr. Nettleship, in 

 the 'St. Thomas's Hospital Reports,' 1880 (vol. 10). 



Testing them with the spectrum, they made most extraordinary 

 mistakes, calling blue, red ; red, green or blue. On cross-examina- 

 tion, it seems that they only distinguish colour by its luminosity ; 

 they always explain that one colour is lighter or darker than another ; 

 evidently their colour names are founded on the observation of what 

 is told them as to the different colours, and not from any real know- 

 ledge of them. The next examination was to get their luminosity 

 curve of the electric light spectrum, and this they did with the very 

 greatest ease. Their readings for the same colour were occasionally a 

 little erratic, differing as much as 5 per cent, from one another, but, 

 by taking the means, their curves come out very concordantly 

 Practically, the curves of the two brothers are identical, the means 

 not differing 2 per cent, from one another at any part of the spectrum ; 

 hence it is unnecessary to give more than one of them. It should be 

 mentioned that both brothers could just catch a glimpse of the red 

 line of lithium when the spectrum of the vapour was on the focussing 

 screen of the apparatus. 



The luminosity curves are shown in the diagram, and the following 

 is the table of observations : 



