ovement whatever throughout our experimentation. We need scarcely
add that with the voluntary control of the giving of the signs, in the
case at least of such small numbers as are here discussed, no errors,
whatever, occurred.

We have discussed the influence of the experimenter, i. e., the one who
asked the horse to tap; now let us consider the influence of others
present upon the horse.

As a general rule, other persons had no effect upon the horse's
responses. This appears from the failure of nearly all tests in which
all of those present--with the exception of the questioner himself--knew
the number which the horse was to tap. Even when the others concentrated
their whole attention upon the number, it profited little as a close
analysis of the 136 cases, which belong under this head in our records,
go to prove. Thus, in the presence of a group of twenty interested
persons--during the absence of Mr. von Osten--twenty-one problems were
given to the horse, the solutions of which were known to everyone but
myself, the questioner. Result: only two correct responses. Only when
there was among the spectators someone to whom the horse was accustomed
to respond or one from whom he regularly received his food, would such
an influence be effective.[L] But such cases were few. The most
important were the following: I at one time whispered a number to Hans
(on the occasion 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 Supplement III (page 255) 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,
however, the number which had been given