STUDIES IN SPECIAL SENSE PHYSIOLOGY 359 

 A. Relative Stimulus Values of different Spectral Region* (Parinawl). 



B. Increased Responsiveness of Peripheral Retina (Dark-adapted). 

 Stimulus : A bluish-white object, 35 degrees in diameter (v. Kries," p. 171).' 



1 Distances from the fovea centralis of any point on the retina can be con- 

 veniently measured in terms of the angle subtended at the nodal point by a segment 

 of the retina cut by a plane passing through the fovea, nodal point, and position of 



Fio. 2. 



the object and bounded by a straight line through the nodal {mint from the object 

 intersecting the retinal segment and by the principal axis. E.g. if A be an object, 

 B tin- nodal ]>oint, and CC a section of the retina, the position (eccentricity) of the 

 image of the point A is denned by the angle a. 



