~ BISULPHIDE OF CARBON. 215 
I now took deep-red glass. 
1st obs, The ants were under the red glass. 
2nd ,, Half of the ants were under each. 
8rd ,, Most of the ants were under violet glass 
and bisulphide. 
4th ,, Half were under each. 
It seemed evident, therefore, that while if violet 
glass alone was placed side by side with red, yellow, or 
green, the ants greatly preferred any of the latter, on 
the other hand, if a layer of bisulphide of carbon, which 
to our eyes is perfectly transparent, was placed over 
the violet glass, they then went as readily, or even 
more readily, under it than under other colours. 
In order to be sure that it was not the mere 
presence of a fluid, or the two layers of glass, to which 
this was due, I thought it would be well to trya similar 
series of experiments, using, however, a layer of similar 
thickness (1 inch) of water coloured light blue by 
ammonio-sulphate of copper. 
I therefore took again the piece of violet glass, over 
which I placed a flat-sided bottle, about 1 inch thick, 
containing a light-blue solution of ammonio-sulphate 
of copper; and, in contrast with it, I used the same 
coloured glasses as before. The difference, however, 
was very marked, the ants always preferring the red, 
green, and yellow to the violet. 
These experiments seem to demonstrate that in 
the previous series the ants were really influenced by 
