BISULPHIDE OF CAEBON. 211 



firom the previous experiments that the bisulphide 

 darkened the nests to the ants more than violet glass, 

 it would appear to do so less than red, green, or yellow. 



I now made some experiments in order, if possible, 

 to determine whether the reason why the ants avoided 

 the violet glass was because they disliked the colour 

 violet, or whether it was because the violet glass trans- 

 mitted more of the ultra-violet rays. 



For this purpose I placed a layer of the bisulphide 

 of carbon over a piece of violet glass. By this arrange- 

 ment I got the violet without the ultra-violet rays ; 

 and I then contrasted this combination with other 

 coloured media. 



First, I took a solution of bichromate of potash 

 (bright orange), and placed it on a part of the nest, side 

 by side with the violet glass and bisulphide of carbon. 

 I should add that the bichromate of potash also cuts off 

 the ultra-violet rays. In all the following observations 

 I changed the position after each observation. 



At 1.30 P.M. the ants were under the bichromate. 



3 „ „ half under the bichromate 



and half under the violet 

 glass and bisulphide. 



8 A.M. „ „ under the bichromate. 

 8.30 „ „ under the violet glass and 



bisulphide. 



9 „ „ half under each. 



9.30 „ „ some under each, but most 



