8 PROCEEDINGS OF THE AMERICAN ACADEMY. 



and blue sensations, the red and violet end points are determined after 

 resting the eye. This requires care in keeping the slit width and 

 illumination constant and in resting the eye for ten minutes or so be- 

 fore the test to approach a steady condition of adaptation. The two 

 junction point filters should be modified by neutral tint glass if 

 needed, so that one need not adjust their luminosity with the slits, 

 but may be able to pass quickly from one standard filter to the other. 

 Both directions of moving the spectrum should be tried to eliminate 

 fatigue effects. 



This method gives quick and certain qualitative diagnosis of any 

 of the cases of simple color aberration (1) to (6). The settings at the 

 red-green and blue-green junctions instantly disclose even a very 

 slight variation in color sense and the end point readings in conjunc- 

 tion show at once whether this variation is due to weakness or abnor- 

 mal strength of red or blue sensations. 



Proceeding further in the analysis of variations one must recognize 

 the probability of variants in which two of the three color sensations 

 are abnormal instead of one as in (1) to (6). These fall into three 

 groups as follows: two sensations weak; two sensations strong; one 

 weak and another strong. 



(7)_R,_G, B 



(8) -R, G,-B 



(9) R,-G,-B 



Also (10) +R,+G, B 



(11) +R, G,+B 

 (12) R,+G,+B 



and finally (13) -R,+G, B 



(14) -R, G,+B 



(15) R,-G,+B 



(16) R,+G,-B 

 (17) +R, G,-B 

 (18)+R,-G, B 



These twelve variations are less easy of diagnosis than (1) to (6) since 

 they depend on more complex quantitative relations. 



Take for example (7). Here the red-green junction may be abso- 

 lutely normal, but the blue-green junction will yield a bluish match 

 showing either weak green or strong blue. The red end point, or for 

 that matter the blue end point, tells the story. Case (8) can be dis- 



