EXPERIMENTS AND OBSERVATIONS 37 



volved the tapping of thirty-two numbers on the part of 

 Hans, and whose position I had carefully ascertained be- 

 forehand. When these were given to the horse to spell, 

 he responded promptly without a single error. Evidently 

 Hans was unable to spell without assistance of some sort 

 from the questioner. 



The horse's reputed aptitude in computation was tested 

 in the following way. Mr. von Osten whispered a num- 

 ber in the horse's ear so that none of the persons present 

 could hear. Thereupon I did likewise. Hans was asked 

 to add the two. Since each of the experimenters knew 

 only his own number, the sum, if known to anyone, could 

 be known to Hans alone. Every such test was imme- 

 diately repeated with the result known to the experi- 

 menters. In 31 tests. in which the method was procedure 

 without knowledge, 3 of the horse's answers were correct, 

 whereas in the 31 tests in which the method was pro- 

 cedure with knowledge, 29 of his responses were correct. 

 Since the three correct answers in the cases in which pro- 

 cedure was without knowledge evidently were accidental, 

 the results of this series of experiments show that Hans 

 was unable to solve arithmetical problems. 



For the purpose of discovering whether the horse could 

 at least count, the Russian kindergarten device, which Mr. 

 von Osten had used in training^ was utilized. The ma- 

 chine was placed before the horse, but the experimenter 

 turned his back upon it. Before each test, a number of 

 balls were pushed to one side and Hans's problem was to 

 indicate the number thus separated. Each test was re- 

 peated with procedure with knowledge. Of eight such 

 experiments Hans responded successfully every time pro- 

 cedure was with knowledge but failed every time pro- 

 cedure was without knowledge. Thus 7 balls were at one 



