BISULPHIDE OF CARBON. 217 



I 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. Kather more than half under the yellow glass. 

 ., 3, Almost all under the violet glass and sulphate 



of quinine. 

 „ 4. Ail „ „ „ „ 



I then took the green glass instead of the yellow. 

 Obs. 1. They were under the violet glass and sulphate 

 of quinine. 



9 



« ^* )> 5J « 



„ 3. Equally divided. 



„ 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 to our eyes, but both of 

 which cut off the ultra-\dolet 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 



