THE LOCAL QUANTITATIVE EFFECT 



123 



27'3 and 50'6 (yellow D line, 589 p-p.), the logarithms of the annulus 

 values of the two apertures being plotted as abscissae and ordinates. 

 For points on the curve the luminosity of the large aperture is equal 

 to that of the small, equality being obtained by means of the annulus. 

 If the luminosity of the spots of light were always equal, irrespective 

 of size, the inclination of the curves would be 45. 





I 3 



& 







1 2 



s 



s 



I' 



+ / / 2 



Log readings with large aperture 



Fig. 41. Equality of brightness curves for different sized apertures. 

 SSN 27-3 =575 MM ; 88 N 50-6 = D line. (Abney.) 



The relation of area stimulated to intensity for the 'periphery of the 

 retina has been studied by Piper 1 , Loeser 2 , Henius 3 , and Fujita 4 . 

 Piper gives the following table for the dark-adapted periphery : 



Area 

 1 



10 



25 



100 



V Area 



or Angular 



size 



1 



3-15 

 5 

 10 



Threshold 

 value 



10-0 



2-94 

 ] -9<; 

 1-02 



Relative 



stimulation 



value 



1 



3-4 

 5-1 



9-8 



Product of angular 



size and threshold 



value 



10-0 



9-3 



9-8 

 10-2 



1 Ztsch.f. Psychol. u. Phyxiot. d. Sinnesorg. xxxn. 98, 1904. 



2 Hirschberg's Festschrift, 1905 ; Feilchenfeld and Loeser. Arck.f. Ophth. i,x. 97, 1905. 



Zlwh.f. Rinnesphysiol. XLIII. 99, 1908. 



* Ibid. XLIII. 243, 1908. 



