282 



Animal Life and Intelligence. 



individual whose colour-range they represent could detect 

 red light in the spectrum up to 800 millionths of a milli- 

 metre wave-length for the right eye, and up to 811 for the 

 left ; and could detect violet light down to 403 and 404. 

 Beyond these limits all was dark. But the last individual 

 in the series, while his range in the violet was about the same, 

 could only detect red light up to 743 and 750 millionths of 

 a millimetre. His spectrum was so much shorter. 



It is seen that there is more variation at the red end 

 than at the violet end of the spectrum, and this notwith- 

 standing that the violet rays are more spread out by the 

 prism than the red rays. It is seen that the two eyes are 

 often markedly different. This is not due to inaccuracy of 

 observation, for certain individuals in which this occurred 

 were tested several times with similar results. It is seen 

 that the variations at the red end and the violet end are 

 often independent, and that the absolute length of the 

 visible spectrum differs in different individuals. 



The following table presents these observations and a 

 few others in another light : — 



The individual N showed signs of colour-blindness, 

 and is therefore not included in the table, but entered 

 separately. He was unable to recognize the C line of the 

 hydrogen spectrum (wave-length 656), which was brilliantly 

 obvious to the normal eye. 



