LIMITS OF VISION. 199 



I arranged so that it passed through a dark box, and 

 tlirew on it the principal colours of the spectrum, 

 namely, red, yellow, green, blue, and violet, as well as 

 the ultra-red and ultra-violet; but the ants took no 

 notice. 



It is obvious that these facts suggest a number of 

 interesting inferences. I must, however, repeat the 

 observations and make others ; but we may at least, I 

 think, conclude from the preceding that: — (1) ants 

 have the power of distinguishing colours ; (2) that they 

 are very sensitive to violet ; and it would also seem (3) 

 that their sensations of colour must be very different 

 from those produced upon us. 



But I was anxious to go beyond this, and to attempt 

 to determine how far their limits of vision are the 

 same as ours. We all know that if a ray of white light 

 is passed through a prism, it is broken up into a 

 beautiful band of colours — the spectrum. To our eyes 

 this spectrum is bounded by red at the one end and 

 violet at the other, the edge being sharply marked at 

 the red end, but less abruptly' at the violet. But a ray 

 of light contains, besides the rays visible to our eyes, 

 others which are called, though not with absolute 

 correctness, heat-rays and chemical rays. These, so far 

 from falling within the limits of our vision, extend fai 

 beyond it, the heat-rays at the red, the chemical rays 

 at the violet end. 



I have tried various experiments with spectra 

 derived from sunlight ; but, owing to the rotation of 



