SIB J. ltjbbook: on ants, bees, and wasps. 363 



veyed to the dark part. In this manner I satisfied myself that 

 the various rays of the spectrum act on them in a different 

 manner from that in which they affect us ; for instance, that ants 

 are speciaUy sensitive to the violet rays. 



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

 mine 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 colors — 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 contaias, 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 far beyond it, 

 the heat-rays at the red, the chemical rays at the violet end. 



I had already tried various experiments with spectra derived from 

 sunlight ; but, owing to the movement of the earth, they were not 

 thoroughly satisfactory. Mr. Spottiswoode was also good enough 

 to enable me to make some experiments with electric light, which 

 have been already recorded ; and I have now to bring before the 

 Society some additional and much more complete experiments, 

 which, through the kindness of Prof. Dewar, Prof. Tyndall, and 

 the Board of Managers, to whom I beg to offer my most cordial 

 thanks, I have been enabled to make in the Laboratory of the 

 Eoyal Institution. 



Prof. Dewar was also kind enough to test my glasses and solu- 

 tions with reference to their power of transmitting color. Taking 

 the wave-length of the extreme visible red as 760 and that of the 

 extreme violet as 397, we have 



760 to 647 give red. 



647 „ 585 „ orange. 



585 „ 575 „ yellow. 



575 „ 497 „ green. 



497 „ 455 „ blue. 



445 ,,397 „ violet. 

 The result of his examination of my glasses and solutions was 

 as follows : — 



The light-yellow glass cut off the high end down to wave- 

 length 442. 

 The dark-yellow glass cut off the high end down to wave- 

 length 493. 



