BISULPHIDE OF CARBON. 217 
T then took the light- yellow glass instead of the dark. 
Obs. 1. The ants were all under the violet glass and 
sulphate of quinine. 
» 2. Rather more than half under the yellow glass. 
», 3. Almost all under the violet glass and sulphate 
of quinine. 
» 4 All ” ” ” ” 
I then took the green glass instead of the yellow. 
Obs. 1. They were under the violet glass and sulphate 
of quinine. 
29 2. 29 ” 29 
3. About half under each. 
4. About three-quarters under the green glass. 
5. Almost all under the violet glass and sulphate 
of quinine. 
Thus, then, while if the ants have to choose 
between the violet and other coloured glasses, they 
will always prefer one of the latter, the effect of 
putting over the violet glass a layer either of sul- 
phate of quinine or bisulphide of carbon, both of 
which are quite transparent, but both of which cut off 
the ultra-violet rays, is to make the violet glass seem 
to the ants as good a shelter as any of the other glasses. 
This seems to me strong evidence that the ultra-violet 
rays are visible to the ants. 
I then tried similar experiments with a saturated 
solution of chrome alum and chromium chloride. These 
11 
