lOO 



E. L. THORNDIKE. 



of the former sort is found in the history of a cat which learns to 

 pull a loop and so escape from a box whose top is covered by 

 a board nailed over it. If, after enough trials, you remove a 

 piece of the board covering the box, the cat, when put in, will 

 still pull the loop instead of crawling out through the open- 

 ing thus made. But, at any time, if she happens to notice the 

 hole, she may make use of it. An instance of the second sort 

 is that of a chick which has been put on a box with a wire screen 

 at its edge, preventing her from jumping directly down, as she 

 would instinctively do, and forcing her to jump to another box 

 on one side of it and thence down. In the experiments which 

 I made, the chick was prevented by a second screen from jump- 

 ing directly from the second box also. That is, if in the accom- 

 panying figure, A is a box 34 inches high, B a box 25 inches 



Fig. 21. 



high, C a box 16 inches high, and D the pen with the food and 

 other chicks, the subject had to go A-B-C-D. The chick 

 tried at first to get through the screen, pecked at it and ran up 

 and down along it, looking at the chicks below and seeking for 

 a hole to get through. Finally it jumped to B and, after a 

 similar process, to C. After enough trials it forms the habit 

 and when put on A goes immediately to B, then to C and down. 

 Now if, after 75 or 80 trials, you take away the screens, giving 

 the chick a free chance to go to D from either A or B, and then 

 put it on A, the following phenomenon appears. The chick 

 goes up to the edge, looks over, w^alks up and down it for a 

 while, still looking down at the chicks below, and then goes 

 and jumps to B as habit has taught it to do. The same actions 

 take place on B. No matter how clearly the chick sees the 



