THE FIELD OF VISION FOR COLOURS 



7'.) 



Since the curves are straight lines it follows that as the intensity 

 diminishes in geometrical progression the angle of field diminishes m 

 a ritli nielical progression. 



The effect of the area of the retina stimulated upon the size of the 

 field may be most conveniently considered here. Charpentier 1 found 

 that for white the size was immaterial so long as it exceeded a diameter 

 of about 0'17 mm. If it were smaller the field remained the same 

 when the brightness was increased in inverse proportion to the size. 



SOr 



Blue 



Yttlow. 

 Red 



Green . 



.Blue. 



Yellow. 



Crven. 



Intensify 



Fig. 32. The temporal and nasal limits of the fields of vision for four spectral colours at 

 different intensities of illumination. (Abney.) 



For colours Abney 2 found that between apertures subtending 4 28' 

 and 10' the fields decrease in extent in such a manner that for each 

 diminution in aperture to half the diameter the diminution in field is 

 5 on the temporal and 4 on the nasal side. 



1 Arch. d'Opht. vu. 13, 1887 2 Abney, p. 208. 



