4 'Journal of Comparative Neurology and Psychology. 



in manufacture, dyeing, ironing, etc. In addition, it is extremely 

 difficult to bend colored papers around glasses or to paste them upon 

 doors so accurately that slight differences in form, size and depth 

 do not apjDcar. To sum uj) these defects under 1, we may say 

 that colored papers afford numerous secondary criteria. 



2. They do not reflect monochromatic bands, but overlapping 

 bands. This is especially true of those reflecting the shorter wave 

 lengths. 



3. The range of intensity ohtainahle in them is so timited, that 

 if any given region of the spectrum should ojfer to the a)iinial a 

 different order of intensity from that ivhich the same region offers to 

 our own eyes, the slight change ivhich ive could introduce in the 

 hrightness of a given stimulus, hy substituting a paper of the same 

 color only lighter or darher {to our own eyes) might not at all 

 reverse for the animal the intensity relation originally existing 

 between the colors. 



Yerkes,* in his work on the dancing mouse, mentions most of 

 these objections and shows by experiment that for that animal the 

 red end of the spectrum is probably extremely weak in intensity. 

 Whether or not the different parts of the spectrum possess the same 

 intensity for the eye of the monkey, as they do for our own, is 

 a question which we have at present no data for deciding, but cer- 

 tainly in the present state of our knowledge we cannot assume such 

 to be the case. 



Believinw^ that many problems in the study of color vision in 

 animals cannot be solved without the aid of a continuous spectrum, 

 and being more or less disJieartened by the failure of colored papers 

 and filters (as they have heretofore been used) to furnish suitable 

 stimuli for testing even the more elementary questions at issue, the 

 writer began work upon a spectral light apparatus which it is hoped 

 will make possible an experimental treatment of the following 

 problems : 



1. Has the animal the power to discriminate between any given 

 color and any other selected color with equal ease, when the relative 



*Yerkes, R. M. The Dancing Mouse. The Macmillan Company, 1908. 



