EXPLANATION OF OBSERVATIONS 147 



numbers, the sole cause of which lay in the difficulty with 

 which tension could be maintained and the body kept 

 motionless for so long a period. These errors occurred 

 in accordance with a certain law. If, for instance, a cer- 

 tain test repeatedly evoked incorrect responses, the 

 questioner would gradually increase the duration of 

 tension and would thus come a little nearer to the desired 

 goal with every test. In this way, Mr. von Osten desiring 

 30 as an answer obtained consecutively the responses, 

 25, 28, 30 ; and I, myself, for the answer 20, received con- 

 secutively the responses 10, 18, 20 (see also the laboratory 

 tests, page 105). Sometimes too, the questioner would 

 flag in his efforts/before the goal was reached. Thus in 

 one of my first tests, I received for the answer 11 the 

 following responses: i, 4, 5, 7, 4. I was unable to get 

 beyond 7. In other instances, the horse responded first 

 with too few and then with too many taps. The correct 

 response therefore could only be obtained after an ap- 

 preciable amount of gauging of tension, as in target 

 practice there must be a gauging of distance. (See 

 page 92). In this way Mr. von Osten obtained for 10 

 the responses 8, 8, 11, 10, and Mr. Schillings for 17, 

 received 9, 16, 19, 18, 18, 14, 9, 9, and finally, after some 

 efforts, 17 taps. Thus there was a rise from 9 to 19, 

 then a fall back to 9 and after eight tests the correct 

 response. As long as we attempt to explain this fact 

 as error on the part of the horse, so long will it remain 

 inexplicable, but the moment we regard it from the point 

 of view of the psychology of the tension of expectation, 

 it becomes perfectly plain. 



The same holds true for the curious predilection which 

 Hans appeared to have for the numbers from 2 to 4, 

 especially for 3 (see page 68). As a matter of fact the 



