SUPPLEMENT IV 

 THE REPORT OF DECEMBER qth, 1904 



Together with Dr. E. von Hornbostel and Mr. O. 

 Pfungst, I have tried during the past few weeks to find 

 an explanation of the accomplishments of the horse 

 ' Hans ' by the experimental method. We had access 

 to the horse in the absence of the master and groom. 

 The results are as follows : 



The horse failed in his responses whenever the solution 

 of the problem that was given him was unknown to any 

 of those present. For instance, when a written number 

 or the objects to be counted were placed before the 

 horse, but were invisible to everyone else, and especially 

 to the questioner, he failed to respond properly. There- 

 fore he can neither count, nor read, nor solve problems 

 in arithmetic. 



The horse failed again whenever he was prevented by 

 means of sufficiently large blinders from seeing the per- 

 sons, and especially the questioner, to whom the solution 

 was known. He therefore required some sort of visual 

 aid. 



These aids need not, however,— and this is the peculi- 

 arly interesting feature in the case, — be given inten- 

 tionally. The proof for this is found in the fact that in 

 the absence of Mr. von Osten the horse gave correct 

 replies to a large number of persons; and to be more 

 specific, Mr. Schillings and later Mr. Pfungst, atter 



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