BELL. — TYPES OF ABNORMAL COLOR VISION. 13 



siderable luminosity, in amount depending on the extent of the red 

 sensation deficit. Those in whom one sensation is nearly or quite ab- 

 sent are of course beyond the chance of help, since balance would 

 require an almost complete obscuration of the remaining sensations, 

 but the theory of the correction rests on a substantial basis and can 

 be put into practice in not too severe cases of partial color deficiency. 

 The method to be followed would be substantially that of Abney in 

 obtaining the sensation curves of the individual and the problem then 

 would resolve itself into making approximate corrections to reduce the 

 curves as nearly as possible to normal relations. In bright light the 

 corrected vision would then show colors in approximately their true 

 relations, though somewhat dulled. 



