EXPERIMENTS AND OBSERVATIONS 71 



were few. The most important were the following: 

 I at one time whispered a number to Hans (on the occa- 

 sion of the tests mentioned on page 37), and Mr. von 

 Osten asked for it the moment I stepped aside. Hans 

 answered incorrectly even though I stood close beside 

 Mr. von Osten ; I did not, however, think intently of the 

 number. As soon as I concentrated my attention upon 

 the number he promptly responded correctly. Further 

 cases are those mentioned on page 38, in which the 

 keeper of the horse unintentionally aided in giving four 

 dates which were unknown to all others present, including 

 the questioner. This single instance shows the necessity 

 of the rule that during tests in which the method is that 

 of procedure without knowledge the solutions should be 

 known to no one of those present. Finally the tests made 

 by the September-Commission and reported in Supple- 

 ment III (page 25s) may possibly belong under this head. 

 Since they were not followed out any further, I am unable 

 to render a definite judgment upon them. In most of 

 these tests the question itself, as put by Mr. von Osten, 

 was not adequately answered, but curiously enough, how- 

 ever, the number which had been given to Hans in von 

 Osten's absence and which formed the initial number of 

 some mathematical operation, was tapped correctly. This 

 may possibly be explained by the assumption that this 

 initial number had been retained in the memory of some 

 of those present, (see page 149, on the " perseverative 

 tendency "), and that the horse, since he had been working 

 with some of them, responded to one of those present. 

 Chance may have played some part also. 



If the questioner knew the number of taps desired, 

 (which was not the case with the tests hitherto discussed), 

 then the environment had still less influence upon the 



