ne's own movements. As in the case of
all other signs given to the horse, these movements were so slight that
they were prone to escape notice even though one's whole attention were
concentrated upon their detection. I also questioned whether in my
attempts to disturb the horse by means of loud calls, it were really the
call or some simultaneous involuntary movement which was the true cause
of the interruption. The doubt was justified, for when I finally learned
to cry out vehemently without making the slightest move, all my crying
was in vain. Also it had seemed to me at first as if I were able to
induce the horse to rear, not only by means of the proper sign or
movement, but also by a mere command, but I found later that in every
case there was always some movement, were it ever so slight. Finally I
tried to simulate voluntarily the oft-mentioned involuntary jerks of the
head. Although it is not very difficult to execute them at will with
almost the same minuteness as when they were performed involuntarily, I
still did not succeed in getting a series of such jerks of equal
fineness throughout. In spite of (and partly on account of) the most
concentrated attention, there would be from time to time a jerk of
somewhat greater extent and energy. As soon as the movement had been
executed, I was able to form a good judgment as to its relative extent,
but I was unable to regulate the impulse beforehand.

With the following comment the chapter will be concluded. Introspections
are necessarily subjective in character. If they are to possess general
validity, they must be borne out by evidence furnished by others--and
this to a greater extent than is necessary for other forms of
observation. It was hardly possible to get corroboration from the other
persons who had worked with Hans, for, although some of them were
excellent observers of external natural phenomena, few of them had had
the necessary amount of practice in introspection. The necessary
confirmation, however, was had in laboratory tests, which we shall
presently describe.

CHAPTER IV

LABORATORY TESTS

The tests which are to be briefly reported here, were begun in November,
1904, and were carried out at the Psychological Institute of the
University of Berlin. The purpose was twofold: first, to discover
whether the expressive movements noted in Mr. von Osten, Mr. Schillings,
and others, were to be regarded as typical and to be found in the
majority of ind