in.] ENGINEERING. 83 



so that there was an interval of about one-third of an inch 

 between the glass and the earth ; but, though the dis- 

 tance was so small, the ants would not jump down, but 

 preferred to go round by the long bridge. They tried in 

 vain to stretch up from the earth to the glass, which, 

 however, was just out of their reach, though they could 

 touch it with their antennae ; but it did not occur to 

 them to heap the earth up a little ; though, if they 

 had moved only half a dozen particles, they would 

 have secured for themselves direct access to the food. 

 This, however, appeared never to occur to them. At 

 length they gave up all attempts to reach up to the glass, 

 and went round by the long paper bridge. I left the 

 arrangement for several weeks, but they continued to do 

 the same. 



Again I varied the experiment, as follows : Having 

 left a nest without food for a short time, I placed some 

 honey on a small wooden brick, surrounded by a little 

 moat of glycerine, about half an inch wide and about T Vth 

 of an inch in depth. Over this moat I placed a paper 

 bridge, one end of which rested on some fine mould. I 

 then put an ant to the honey, and soon a little crowd 

 was collected round it. I then removed the paper 

 bridge ; the ants could not cross the glycerine, they came 

 to the edge and walked round and round, but were unable 

 to get across ; nor did it occur to them to make a bridge 

 or bank across the glycerine by means of the mould which 

 I had placed so conveniently for them. I was the more 

 surprised at this, on account of the ingenuity with which 

 they avail themselves of earth in constructing their 

 nests. For instance, wishing, if possible, to avoid the 

 trouble of frequently moistening the earth in my nests, 



G2 



