THE FIELD OF VISION FOR COLOURS 



79 



Since the curves are straight lines it follows that as the intensiti/ 

 diminishes in geometrical progression the angle of field diminishes in 

 arithnietical progression. 



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

 field may be most conveniently considered here. Charpentieri 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. 

 60r 





40 



50 



BO 



10 



Blue 



Yellow 

 Red. 



Green . 



Blue. 



Ynlow. 

 Red. 



Gi-een. 



Intensity 



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^ 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, 18S7. '^ Abney, p. 208. 



