Two Cases of Congenital Night- Blindness. 



73 



S.S.N. 



58. 



56. 



54. 



52. 



50. 



48. 



46. 



44. 



42. 



40. 



38. 



36. 



34. 



E 

 N 



B 



N 



1-12 



0-97 



1 -12 



1-00 



1-06 

 1 -00 



1-00 

 1-02 



1-00 

 1-62 



0- 98 



1- 00 



1-00 

 1-03 



0- 92 



1- 08 



0-90 

 1 -08 



0-93 

 1 -08 



0- 96 



1- 10 



1-02 

 0-94 



1 -05 

 1-05 



Allowance has to be made for a difference in pigmentation of the foveal 

 region. It has been shown in my recent communication on the fourth sensa- 

 tion that the added luminosity of the sensation of this fourth sensation is 



Extinction of Colour & Light in the Spectrum 

 by 2 Congenita! night-blind persons. 



2.005 



2000 



3 



O 



o 

 o 



c 

 o 



o 

 c 



3.005 X 

 o 



3.000 



S.N 30 32 34 36 38 40 4^ 44 46 48 50 52 54 56 58 60 



Spectrum Scale 



negligible when the spectrum is of normal brightness (say when the D ray is of 

 J candle-power brightness at foot distance from the screen). These measures 

 show that the luminosity of such a spectrum is, within the limits of error, the 

 same in both cases. 



