THE THRESHOLD OF VISION FOR DIFFERENT COLOURED LIGHTS. 
97 
obtained with the two instruments. In Table I. will also be found the wave-lengths 
corresponding to the dispersion scale, the readings of which are indicated by the 
letters SSN, and which are used throughout this paper to indicate the different colours. 
In Table II. are given the results obtained by eight observers. Of these A. and W. 
are the authors, and B. is Mr. W. Brapfield, the assistant in the Colour Vision 
Laboratory, to whom we are very much indebted for great assistance throughout the 
work. Observers T., Bk., Ar. and B. were students in the advanced Physics Class, and 
N. is one of our colleagues. Of these observers A., W., B., T. and Bk. have normal 
colour vision, Ar. and N. are dichromates, Ar. being green blind (deuteranope) and N. 
red blind (protanope), while R. is a case of a displaced green sensation curve whose 
case has already been described in a previous paper (‘ Roy. Soc. Proc.,’ A, vol. 89, 232, 
1913). Observations were in each case made throughout the spectrum using central 
fixation, and also with the fixation spot 1'25, 2‘5. 5, and 10 degrees shown above the 
centre ol the disc on which the stimulus light was received. 
