12 PROCEEDINGS OF THE AMERICAN ACADEMY. 



study of minor variation in color sensations the color fields ought to 

 be more thoroughly investigated than is usual. 



In conclusion the following list shows the tabulation of all types of 

 abnormality here considered, those which the writer has observed or 

 found recorded being denoted by an asterisk. 



Simple Binary Ternary 



(1)+R, G, B* (7)-R,-G, B* (19) +R,+G,+B 



(2) R,+G, B* (8) -R, G,-B* (20) +R, + G,-B 



(3) R, G,+B* (9) R,-G, B (21) +R,-G,+B* 



(4) -R, G, B* (io) +R,+G, B (22) +R,-G,-B 



(5) R,-G, B* (ii) _|_r } g,+B (23) -R,-G,-B* 



(6) R, G,-B* (12) R,+G,+B (24) -R, + G,-B* 



* 



(13) -R.+G, B* (25) -R,-G,+B 



(14) -R, G, + B* (26) -R,+G,+B 



(15) R,-G,+B* 



(16) R,+G,-B 



(17) + R, G,-B 



(18) +R,-G, B 



The writer will be grateful for notes on any of the missing types in the 

 table which may have escaped notice in the very scattered literature 

 of this intricate subject. 



A study of these types inevitably leads to the question as to whether 

 any remedial measures can help the victims of abnormal color vision. 

 Within restricted limits the answer may be affirmative. The method 

 which has to be followed is precisely that which has already been tried 

 with considerable success in modifying the color of artificial illumi- 

 nants to obtain normal daylight values of color viewed by them. An 

 ordinary gas flame, for example, is in effect partially blue-blind and 

 the normal eye will see colored objects under such a light very much 

 as the partially blue blind would see them in daylight. The necessary 

 correction has been found to be the interposition of absorbing media 

 which reduce the green and red elements in the same degree as the de- 

 ficit of the blue element in the source. The penalty of doing this is the 

 loss of considerable luminosity. The selective screens for this purpose 

 are highly effective subject to this limitation. By a process exactly 

 analogous it should be possible to provide a certain proportion of the 

 partially red blind with spectacles which would give them at least an 

 approximation to normal color vision, although at the expense of con- 



