ar I have supposed the horse to be a
never-failing mechanism and that I have placed all errors to the account
of the questioner. The horse never failed to note the signal for
stopping and therefore never was the immediate cause of an error. It is
not to be denied that now and then he would cease tapping spontaneously
and in this way would become the cause of an error. We have no data on
this point, but undoubtedly the horse's share in the total number of
errors was very slight.

(_b._) Another source of error was faulty computation on the part of the
questioner. The questioner made the signal for stopping when the
expected number of taps had been reached. The horse faithfully mirrored
the miscalculation of the questioner. I have knowledge of only one such
case. The journals report that once Mr. von Osten, when someone called
to his attention that Hans had indicated the wrong day of the week,
replied: "Yes, you are right, it was not Thursday, but Friday,"
whereupon Hans being asked again, promptly responded correctly. This
appeared to the reporter in question as proof of the subjective
influence of Mr. von Osten upon the horse.

(_c._) When errors in calculation and failures in proper concentration
combine, i. e. when the questioner makes a mistake in calculation
because he is excited or inattentive and for the same reason does not
make the movement, which is the signal for stopping, in accordance with
the number which he deems to be the correct answer, then the result is
usually wrong, but it may be correct in the few cases in which the two
errors exactly compensate each other. Nothing has been so effective in
establishing Hans's reputation, nothing has brought him so many
followers, as these cases in which he, rather than his mentor, has been
in the right. Compared with the mass of cases in which Hans was wrong
these latter cases are diminishingly few in number, yet these few made
such an impression upon the observers that their number tended to be
overestimated. As a matter of fact, I have been able to discover records
of only seven such cases. Two of these were reported by the Count zu
Castell. On the 8th of September, he entered the horse's stall, alone,
and believing it to be the seventh day of the month, he asked Hans the
date. The horse responded correctly with 8 taps. At another time he held
up before Hans a slate on which were written the numbers 5, 8 and 3 and
asked the horse to indicate their sum which in th