This, it
will be remembered, was the usual position of the questioner when
working with the horse. Three levers were attached to his head in such a
way that every movement backward or forward would act upon the first
lever, every movement to the right or left would move the second, and
every movement of the head upward or downward would be recorded by the
third. With regard to the sensitivity of the machine, micrometric
determination showed that when the subject was properly installed,
movements through so small a distance as 1/10 millimeter could be
accurately ascertained. The subject was carefully instructed to remain
as quiet as possible, but without constraint. Voluntary movements were
thus obviated. But the question arose: were not the involuntary
movements thus suffering a loss?--And it was upon them that we were
experimenting. The question cannot be put aside summarily, but
experience taught us that the movements in question, nevertheless, did
appear quite effectually, if one could have the right kind of subjects
at one's command. We need hardly mention that besides the two persons
immediately concerned--I, myself, attended to the apparatus--there was
no one else present, and that the subject was not allowed to see the
curves produced on the kymograph. Besides the registration of the
head-movements, I also undertook to register the respiratory-movements
of the subject. This was done by means of the so-called pneumograph,
attached to which was a lever recording the thoracic expansion and
contraction. This was for the purpose of ascertaining the relationship,
which might eventually be found to exist, between the release of psychic
tension, on the one hand, and respiration, on the other.

The subject was now told to think of some number, which, of course, was
unknown to me. At a given moment I was to tap upon one of a series of
keys arranged like those of a piano, with the middle finger of my right
hand--corresponding to the right forefoot of the horse. The questioner
observed my key, I, his head,--just what had happened in the experiments
with Hans,--and as soon as I perceived the involuntary closing signal I
reacted upon it by releasing, suddenly, another key upon the same
keyboard, which I had in the meantime been pressing down with my second
finger, thus marking what with Hans had been called the backstep. Each
key was connected with a separate electro-magnet, and these in turn with
markers, in such a manner tha