LIMITS OF VISION. 199 
I arranged so that it passed through a dark box, and 
threw 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 fer 
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 
