146 INTELLIGENT BEHAVIOUR 
extended from the top of the door downwards, and over the 
whole area, would thus inevitably at some time or other reach the 
handle of the latch, which was thus struck forcibly downwards, 
the latch itself rising upwards. The door would then open 
from the weight of the dog pushing against it. The dog 
always opened the door in this manner from the time when 
the incident was first noticed until he left, a period of about 
three years. The door was opened with no greater ease at 
the expiration of that period than at the commencement. 
His paws would strike various parts of the door, and he never 
appeared to exercise any degree of judgment in the localization 
of his strokes, the fact of his paws striking the handle of the 
latch being a necessary result, providing the dog had sufficient 
patience and strength to continue.” 
One or two more experiments with my fox terrier may be 
briefly described. I watched his behaviour when a solid 
indiarubber ball was thrown towards a wall standing at right 
angles to its course. At first he followed it right up to the 
wall and then back as it rebounded. So long as it travelled 
with such velocity as to be only just ahead of him he pursued 
the same course. But when it was thrown more violently, 
so as to meet him on the rebound as he ran towards the wall, 
he learnt that he was thus able to seize it as it came 
towards him. And, profiting by the incidental experience 
thus gained, he acquired the habit—though for long with 
some uncertainty of reaction—of slowing off when the 
object of his pursuit reached the wall so as to await its 
rebound. Again, when the ball was thrown so as to glance 
at a wide angle from a surface, at first—when the velocity 
was such as to keep it just ahead of him—he followed its 
course. But when the velocity was increased he learnt to 
take a short cut along the third side of a triangle, so as to 
catch the object at some distance from the wall. A third 
series of experiments were made where a right angle was 
formed by the meeting of two surfaces. One side of the 
angle, the left, was dealt with for a day or two. At first the 
ball was directly followed. Then a short cut was taken to 
