166 Dr. F. W. Edridge- Green. [Nov. 15, 



and green in any mixture can be ascertained. For instance, 12*73 corresponds 

 to a ratio of intensity 1 - 061 green/red, and 10"371 to 0-5829 green/red. 

 The other figures can he easily understood by remembering that a difference 

 of one-tenth of a division corresponds to a difference of about 1\ per cent, 

 in the ratio of intensities of red to green when the figures are in the 

 neighbourhood of normal vision. 



Out of the hundred examined, 86 made the normal equation or within one 

 division on either side of it, 12 were anomalous trichromats, 10 being red- 

 anomalies and 2 being green-anomalies. 



R«d-anomalies. Green-anomalies. 



, A N 



1. 1-5 6. 1-2 1. 31 



2. 1-4 7. 1-8 2. 1-3 



3. 1-2 8. 2-5 



4. 15 9. 1-3 



5. 1-3 10. 13 



Two others on an average of five observations appeared as anomalies (one 1 - 3 red, the 

 other 2 - green), but, as they both agreed with the normal equation, they do not come 

 under the definition. 



Excluding the last mentioned, who were to a certain extent colour blind, 

 none of the anomalies were found to be colour defective. Of those who made 

 the normal match 9 were found to be colour defective. 



No. 1 of the green-anomalies was examined very carefully on three 

 occasions ; there was no evidence of colour-blindness ; she passed my ordinary 

 lantern test and also my triple lantern with ease and accuracy, and saw red 

 and green through small apertures as far as I did. She also passed my bead 

 test. 



Examination with Spectrometer. — Pure yellow was isolated at \ 5770 to 

 \ 5882. This is quite normal. The area of greatest luminosity was \ 5697 

 to \ 5795 ; this is considerably to the green side of the maximum of the 

 normal luminosity curve. She marked out 18 monochromatic divisions in 

 the spectrum. This is the normal number ; she also named all the colours 

 red, orange, yellow, green, blue, and violet correctly. 



I have also examined a large number of men and find that when there is a 

 large mean deviation there is colour weakness. The following case is 

 instructive as an example of a high grade green-anomaly without any trace of 

 colour weakness. 



The observer was an assistant in the Chemical Laboratory of the Physiological 

 Institute, University College. 



Rayleigh Apparatus. — Shown red and yellow, named them correctly as red and yellow. 

 The mean of seven equations was 17 - 3, the mean deviation O'l. 

 The normal equation was 14 5. The mean deviation is very small. 



