Chapter V: Explanation of the Observations (3)

It is easy to explain the musical accomplishments. The tones which were played for the horse, were known to Mr. von Osten, since he himself played the harmonica, or when someone else played it, he, Mr. von Osten, could see the stoppers. He then thought of the number which indicated the tone in question, and Hans would tap it. Thus arose the tale of the horse's absolute tonal memory. This tale gained much support at the time, from an experience which has been recounted to me by the well-known composer, Professor Max Schillings. It shows more clearly than any other report how very confused were the threads that had been spun in the whole matter. In order to test the horse's musical ability Prof. Schillings played, let us say, three tones upon the accustomed instrument. Complying with Mr. von Osten's wish, Prof. Schillings always indicated which three he was about to play. The horse always tapped them correctly. In order to make a decisive test, Prof. Schillings then played, without anyone's knowledge, a note that was in reality a third below the one he had indicated to Mr. von Osten. Curiously enough, Hans tapped, as a matter of fact, the number indicating the note that was actually struck, and it was only in the third repetition and after many exhortations on the part of the master "to have a care", that the horse finally tapped the number indicating the note Mr. von Osten had in mind and which in truth was the wrong one. This curious experiment seemed to those to whom Professor Schillings communicated it, to yield conclusive evidence of the horse's absolute hearing. As a matter of fact, however, Prof. Schillings had unwittingly, and, contrary to any intention on his part, inspired the horse. Standing, as he did, just behind the right shoulder of the horse, he was able to interrupt Hans (who had begun to tap in response to a move on the part of Mr. von Osten,) by means of an involuntary movement which did the work of a closing signal. At the same time Mr. von Osten, likewise standing to the right of the horse and expecting more taps, remained perfectly quiet. (This is as it was in the tests, mentioned on page 71, in which, of two experimenters, one started the horse tapping, and the other stopped him.) Mr. von Osten very probably lost patience after Hans had seemingly given the wrong response twice, and thereupon came nearer to the horse and thus by monopolizing its attention--so as to exclude Prof. Schillings--he was able to get the response so ardently desired.[AF] When, in tests such as these, two stoppers were opened and thus two notes sounded, Mr. von Osten would count the number of stoppers intervening between the two, and Hans would tap the number. And so arose the tale of Hans's knowledge of musical intervals. Whenever the two notes were sung or whistled, in which case there would be no stoppers that could be counted, then Mr. von Osten, who was quite destitute of musical knowledge, was at a loss, and also Hans. If, however, the intervening notes were sung, then everything went smoothly once more. Major and minor chords were regularly characterized as "beautiful", all others as "bad", (but even here errors occurred). A musician had taught Mr. von Osten these distinctions. The old man also knew the melodies that were played on the hand-organ. Each one had a number assigned to it, and Hans was required to tap the number of the melody in token of recognition.--Hans was as ignorant of musical time, as he was of melody, and all attempts to get him to march in regular step were utterly futile. A number of musical tests were made in the absence of Mr. von Osten. In these Mr. Hahn undertook the questioner's role, and since he had had musical training, he was aware of what the numbers should be, even when he could not see the stoppers of the harmonica, and, therefore, we readily understand why it was that the horse responded so wonderfully in his case.

[Footnote AF: General Noizet[79] has left us a story of the middle
of the last century, which in essential detail corresponds closely
with the one just given. The scene is a French chateau and the hero
is--a rapping table, highly prized on account of the intelligent
answers it could give. Seated about it were a number of ladies and
at the other end of the room sat a French savant, a member of the
Academy. The ladies requested him to put a simple mathematical
question to the table, and complying with their request, he asked
for the cube root of 4. None of the ladies who sat about the table
knew the solution; the table unhesitatingly gave 6 raps. This answer
was refused as incorrect. The table was asked to try again, and
again it wrapped 6. For this it was bitterly reproached. Hereupon
the questioner, who during the whole time had remained in his place
at the other end of the room, came forward with the confession that
the table was innocent, that he had made a mistake. He had asked for
the cube root of 4, but had really meant to ask for the cube of that
number, viz., 64, and the table had as a matter of fact given the
first numeral of that number.

One is immediately struck by the analogy between this case and that
of Professor Schillings. In both cases those immediately concerned
(the women in the one, Mr. von Osten in the other) believe that a
wrong answer is being given repeatedly. The cause of the error lies
in a person who seemingly is not concerned with the response. (The
Frenchman asked the question, but did not sit at the table.
Professor Schillings sounded the notes, but it was Mr. von Osten who
got the horse to tap.) In both instances the questioner asks one
thing, but had something else in mind. (With the Frenchman it was a
slip of the tongue; Mr. Schillings did it purposely.) And finally,
in both cases the response corresponds not to the question that has
been asked, but to that which has been thought, so that, though
seemingly wrong, the responses of both table and horse were really
correct. By way of explanation, Noizet believes that he has a case
of true thought-transference or "telepathy" (page 108). The
questioner watched with utmost attentiveness the rapping of the
table, and the women in turn regarded the man. And thus, Noizet
believes, the man's thought was transferred to the minds of the
others without the mediation of eye or ear, etc., and hence
unvitiated by the words that had been spoken. I myself prefer
another explanation. At that moment in which the rapping arrived at
the expected number, the Frenchman executed a movement
characteristic of release of tension and to this the women of the
circle reacted. It was not necessary that they should be able to
account for this afterward, (just as sometimes occurs in the case of
thought-readers[80]). It is very probable, too, that they were not
of a very reflective turn of mind anyway. We are warranted, I think,
in regarding the two cases as identical in kind.]

The so-called musical ability of horses appears, from all that is known, to be confined within very narrow bounds. Only one fact is universally accepted, viz., horses of the military are believed to possess a knowledge of the significance of trumpet signals, and are often said to interpret them more readily than the recruits.[81] Since no experiments had been made along these lines, I undertook to make a brief test of the cavalry horses mentioned on page 188. As in the preceding tests, the three animals were arranged behind one another with the customary distance of two horses' lengths between, and each was ridden by his accustomed rider. They were held by the reins, but received no aid of any kind, either to start them or to restrain them. A bugle then sounded the various signals at the other end of the barrack's courtyard. We had been previously assured that the horses would certainly react without fail. But, as a matter of fact, the result was quite the contrary. Two of the horses did not move at all, and the third, a thirteen-year old gelding, was startled nearly every time and would tear off in a gallop--even though a trot had been sounded. I would not, however, venture to draw any conclusions from results such as these. Many more tests would have to be made, and some of them upon the whole squadron, before a judgment could be given.[AG]

[Footnote AG: Professor Fluegel,[82] basing his statements on an
article appearing in "Schorer's Familienblatt" (Berlin, 1890, No. 8,
p. 128), gives an account of similar experiments which were supposed
to have been conducted by the Zoological Society for Westphalia and
Lippe, and presumably showed that "the horses of the military do not
understand the bugle calls." No matter how well trained a horse may
have been, it would not respond to a signal. This report, however,
is due to a mistake. Such experiments have never been made by the
society mentioned, so I am told by its director, Dr. Reeker. Nor do
I know of any one else who has made experiments of this kind.
However, Professor Landois,[83] the eminent zoologist, now deceased
(founder of the scientific society mentioned), tested four
circus-horses for their musical ability and specifically for their
sense of musical time. He arrives at the conclusion that horses
"have no feeling for time, whatsoever." With but few
exceptions,[84, 85] all experts to-day are of the same opinion.
Horse-trainers, especially, are universally agreed on this point. It
is easy to see in any circus performance that it is not the horses
that accommodate themselves to the music, but that the music
accommodates itself to them, and that the trained horses[86] are
induced to do their artistic stepping only by the aids given by
their riders. Furthermore, all these horses are trained without the
use of music.----It would therefore appear that the time had arrived
when the tales of the dancing horses of the Sybarites ought no
longer to gain credence. Two Greek writers, Athenaeus[87] and
AElian,[88] tell us that the inhabitants of Sybaris, far-famed for
their luxurious habits, had trained their horses to dance to the
music of flutes during their banquets. Building upon this, the men
of Crotona, in one of their campaigns against the Sybarites, ordered
the flute-players to play the tunes familiar to the Sybarite horses.
Immediately the well-trained steeds began to dance, thus throwing
the whole Sybarite army into confusion, and the men of Crotona won
the day. (The same story is told in more detail concerning the
horses of the inhabitants of Cardia. Both accounts, somewhat mixed,
are to be found in Julius Africanus,[89] a writer of the third
century of the Christian era.)--In recent years a French veterinary
surgeon, Guenon,[90] experimented on the effect of music upon the
horses of the military. He entered their stalls, playing upon a
flute, and noted their behavior. Four-fifths of the animals, he
says, were deeply moved, yes, delighted, even, ("charmes." One
interpreter[91] calls it a case of hypnosis!). This emotional
excitement was expressed--somewhat unaesthetically--by the dropping
of excrementa. Guenon characterizes the feeling-state of these
animals as being a mixture of pleasure and astonishment, of
satisfaction and excitement ("melange de plaisir et d'etonnement, de
satisfaction et de trouble.") He also asserts that the horse's
musical taste is similar to our own. But I can find nothing in his
whole exposition which might prove this. Indeed there is nothing
that could be interpreted as anything other than a purely sensuous
effect upon the horses. I may go a step farther and say that thus
far the sense of music, i. e., understanding of melody, harmony and
rhythm, has not been shown to exist in any animal. Some animals may,
however, be susceptible to the sensuous pleasantness of the tones
themselves.]

I shall now turn to peculiarities of character, highly humanized, which have been attributed to Hans. His "sympathies" and "antipathies", so-called, were nothing but erroneous appellations for the success or failure on the part of the respective individuals to elicit responses. He who could procure answers frequently, apparently stood high in the horse's favor. That Hans shook his head violently when asked by Mr. von Osten: "Do you like Mr. Stumpf?", and answered in the affirmative the further question: "Do you like Mr. Busch?", was nothing but a confession--unwilling, to be sure--on the part of the master himself. In the first case the master thought "no", in the second instance, "yes", and the two thoughts were accompanied by the corresponding head movements, to which Hans responded mechanically. Hans appeared to be well-disposed toward me, but evidently because I always rewarded him liberally when he answered correctly, and I did not scold him when his responses were wrong, as did Mr. von Osten and Mr. Schillings, who instead of seeking the cause within themselves, were always ready to rebuke Hans for his contrariety and fickleness. The horse did not show, in so far as can be judged at all, any real affection for his master. On the other hand it would be unwarranted to say that, in spite of all rewards, he developed a grudge against all those who bothered him with instruction and examination. Shortly after the close of our experimentation it happened that Hans severely injured his groom by a blow in the face. Yet this man had always been very gentle with the horse and had been forbidden by Mr. von Osten to make Hans solve any problems for him. Experts assure me that we have here to deal, not with a case of "moral insanity", but with a very common experience,--although this view will probably be cavilled at by enthusiastic lovers of horses. The work of so excellent an expert as Fillis,[92] for instance, bears us out in this respect.

The horse's supposed fickleness was nothing but a token of the fact that even those who were accustomed to working with him, did not have him completely in hand. (They simply did not understand how to obtain correct responses from the horse.) It often happened that in the evening, when it had become so dark that the movements of Mr. von Osten could no longer be seen, Hans had to suffer bitter reproaches because he made so many errors. That, in truth, he never was stubborn and that the cause of failure really lay in the questioner, is shown by the fact that the mood, for which he was reproved, would disappear the moment the questioner voluntarily controlled the signals. We may add that there was no basis for the assumption that "he had an uncommon, finely constituted nervous system" or was possessed of a "high degree of nervousness". Both these phrases were often mentioned by way of explanation. Hans was restive, as horses usually are. And besides, he lived a life so secluded (he was never allowed to leave the courtyard) that as a result he was easily disturbed by strange sights and sounds. There was not the slightest trace of the clinical symptoms of neurasthenia--on the contrary he gave the impression of perfect health,--which was curious enough when we remember his rather unnatural mode of life.

Hans's stubbornness was a myth. He was suspected of it whenever the same error occurred a number of times in succession, i. e., when the questioner did not properly regulate his attention (page 146) or when he was being controlled by "perseverative tendency", mentioned on page 149. Mr. Schillings, who has provided me with material here as elsewhere, relates the following episode which occurred on one such occasion. To one and the same question put alternately by Mr. von Osten and Mr. Schillings, Hans responded correctly, with two taps, to the former, and just as persistently incorrectly, with three taps, to the latter. After Mr. Schillings had suffered this to occur three times he accosted the horse peremptorily: "And now are you going to answer correctly?". Hereupon Hans promptly shook his head, to the great merriment of all those present. (Mr. Schillings had, with no accounted reason, expected a "no".) Hans was called willful whenever the same question was successively answered by different responses, as frequently happened with the increasing tension that characterized the high numbers (page 145). He was also regarded as stubborn when no reply at all was forthcoming, as in the tests with the blinders.

Hans's supposed distrust of the questioner, when the latter did not know the answer to the problem, is nothing but a poor attempt to account for the failure of those tests. Hans's distrust of the correctness of his own responses was supposed to be evident from his tendency to begin to tap once more if, after the completion of a task, the questioner did not immediately give expression to some form of approval or disapproval--just as a schoolboy begins to doubt his answer if the teacher remains silent for a short time. In terms of the results of our experimentation this would mean that whenever the questioner did not resume the erect posture, after Hans had given the final tap with the left foot, then the horse would immediately begin once more to tap with the other foot (page 61).

As the evil characteristics, so, too, the good. Thus, his precipitancy, which was supposedly evidenced by his beginning to tap before the questioner had enunciated the question, was nothing but a reflection of the questioner's own precipitancy in bending forward (page 57). Never did Hans evince the slightest trace of spontaneity. He never spelled, of his own accord, anything like "Hans is hungry," for instance. He was rather like a machine that must be started and kept going by a certain amount of fuel (in the form of bread and carrots). The desire for food did not have to be operative in every case. The tapping might ensue mechanically as a matter of habit--for horses are to a large extent creatures of habit. This lack of spontaneity could hardly be reconciled with the horse's reputation for cleverness. It would not be necessary to touch upon the signs that were supposed to betoken genius: the intelligent eye, the high forehead, the carriage of the head, which clearly showed that "a real thought process was going on inside",--all these, we said, would not need mentioning, if they had not been taken seriously by sober-minded folk. If there is a report that Hans turned appreciatively toward visitors who made some remark in praise of his accomplishments,--it is evidence only of the observer's imaginativeness.

Turning from a consideration of the horse to that of the persons experimenting with him,[AH] the first and most important question that arises is this: How was it possible that so many persons (there were about forty) were able to receive responses from the horse, and many of them on the very first occasion? The answer is not hard to find. All of these persons came to the horse in very much the same frame of mind--which found a similar expression in all, in both posture and movements. And it was these motor expressions of the questioner (aside from the signs for "yes" and "no", which I believe I have adequately explained on page 98), that the horse needed as stimuli for his activity.

[Footnote AH: I cannot enter upon a discussion of the latest
psychological problems, here involved, partly because that would
take us beyond the purpose of this monograph, and partly because
they are still moot questions and hence not suited to popular
treatment. Briefly though, they are these: What is the nature of the
relationship between cognitive and affective states on the one hand
and involuntary, (so-called expressive) movements on the other? Is
this connection an external thing, as it were, an association
arising as a habit formation, or does every idea partake essentially
of a motor character? Do purely cognitive states give rise to such
movements, or does the movement impulse depend more particularly
upon the affective consciousness accompanying the cognitive states?
And in how far do given kinds of expressive movements depend upon
certain ideational types (c.f. page 95)? Thus, what is the
influence of the visual image upon the gestures for "up," "down,"
etc.? And then, are these involuntary movements, when not noted,
truly unconscious, or merely not attended to,----in other words, are
they beyond the pale of consciousness or merely "at the fringe?" The
various writers speak almost without exception of unconscious
movements in the strict sense of the term. My own introspections,
however, have led me to doubt whether they are quite unconscious.
Since I have attained some practice I am able to describe in detail
(under conditions of objective control) my involuntary movements, no
matter how slight, even down to mere muscular tensions. None of my
subjects, however, has as yet succeeded in this. It is no very easy
matter to be on the lookout for some unknown movements which might
eventually occur, while attempting to concentrate attention to the
utmost upon a certain definite ideational content, for this very
dividing of attention effects a decrease in the force of the
movement, and thus makes it all the more difficult to discover. From
my own experience, however, I am inclined to believe that these
movements are not unconscious, but merely unattended to, in other
words, we have a narrowing down of the apperceived content within
certain limits, but not a narrowing down of consciousness, (much
less a "splitting" of consciousness or of personality as the thing
unfortunately has sometimes been called). In order, however, not to
be guilty of premature judgment, I have avoided the terms
"unconscious" and "unattended to," and chose expressions which leave
these finer distinctions untouched.]

The next question that arises is: why did only a few persons receive responses regularly from Hans, whereas the greater number were favored only occasionally? What was the selective principle involved? The answer is, that the successful person had to belong to a certain type, which embodied the following essential characteristics.

1. A certain measure of ability and tact in dealing with the horse. As in the case of dealing with wild animals, such as the lion, etc., Hans must not be made uneasy by timidity in the questioner, but must be approached with an air of quiet authority.

2. The power of intense concentration, whether in expectation of a certain sensory impression (the final tap), or in fixing attention upon some idea-content ("yes", "no", etc.). It is only when expectancy and volition are very forceful, that a sufficient release of tension can ensue. This release of tension is accompanied by a change in innervation and results in a perceptible movement. And it was only when the thought of "yes", or "up", etc., was very vivid, that the nervous energy would spread to the motor areas and thence to the efferent fibers, and thus result in the head-movement of the questioner. From infancy we are trained to keep all of our voluntary muscles under a certain measure of control. During the state of concentration just described, this control is relaxed, and our whole musculature becomes the instrument for the play of non-voluntary impulses. The stronger the customary control, the stronger must the stimuli be which can overcome it. The steady unremitting fixation, which resulted in the horse's selection of the cloths, also involves a high degree of concentration.

3. Facility of motor discharge. Great concentration was necessary of course, but not sufficient. Persons in whom the flow of nervous energy tended to drain off over the nerves leading to the glands and the vascular system might betray great tension, not so much by movements as by a flow of perspiration (we have many excellent examples of this given by Manouvrier)[93] or by a violent beating of the heart, blushing and the like,--in short, by secretory and vasomotor effects. Or it is not inconceivable that long dealing with very abstract thoughts might have weakened the tendency of overflow to other parts of the brain, and that therefore the entire discharge is used up in those portions of the brain which are the basis of the intellectual processes. But if expressive movements occur, the motor pathways must be particularly unresisting in order to take up the overflow of psychophysic energy. This is the necessary condition for obtaining the tapping and the head movements on the part of the horse, although for the tapping there is still one other circumstance necessary: viz.,

4. The power to distribute tension economically--i. e., the ability to sustain it long enough, and to release it at the right moment (after the manner of the curves described on page 93), and to control properly the unavoidable variations which will occur.[AI]

[Footnote AI: The mental state just described is probably
essentially the same as that of the spiritualistic "mediums" when
they are occupied with table-rapping and table-moving. In both cases
concentration is very intense,----in other words, the field of
attention is limited. We saw that this state not only favors the
tendency toward involuntary movement, but on account of the
absorption of the individual's attention by a certain limited
content, the person will be unaware of the voluntary movements as
they occur. And we are not necessarily here dealing with
neurasthenic, hysteric, or other diseased nervous conditions. In the
case of table-rapping there are movements of the hands, in our case
there are those of the head. Our head, balanced as it is upon the
cervical vertebral column, is continually in a state of unstable
equilibrium and therefore peculiarly susceptible to
movement-impulses of every kind. But I could induce not only
movements of the head, but also of the arms and legs, and this by
having the subject assume a posture which enabled him to hold arms
or legs in as unstable a position as possible. He might stretch out
his legs horizontally before him, or he could raise them vertically
upward as in the hand-stand in gymnastic work. An extract from a
treatise by Count A. de Gasparin,[94] which appeared about the
middle of the last century, may serve to show how close the
correspondence between the two processes, that of getting the table
to rap and that of causing Hans to respond, really is. The report of
this writer, based upon the detailed record of his tests in
table-moving and table-rapping, closely parallels in many minute
details the observations which were made in the course of our
experimentation with Hans. The case is all the more remarkable when
we bear in mind that this writer did not seek the cause of the
phenomena, as we did, in involuntary movements, but thrusting aside
this explanation, he posited the cause in the agency of some
mysterious fluid. It may not be amiss to say that this as well as
most other references were consulted after the present experiments
and introspections had been completed. Of the page references
preceding the following citations, the first always refers to the
page in the French original, and the other, enclosed in brackets, to
the parallel passage in the present monograph.

P. 49 [31]. Some questioners are especially suitable
("experimentateurs hors ligne"), but in their absence, other persons
may also operate successfully ("le succes, quoique moins brillant
alors, n'est pas impossible.")

P. 25 [229]. But even the most suitable questioners do not always
succeed equally well ("les plus surs d'eux-memes ne reussissaient
pas egalement tous les jours.")

P. 42 [151]. When the questioner is in any way indisposed, the
measure of success is also less.

P. 91 & 87 [150]. The Questioner must first get into the sweep of
things ("en train"), and once he has done so, all interruption
whatsoever must be avoided.

P. 91 [93]. Unless there is sufficient tension on the part of the
questioner, the test will fail. ("La volonte est-elle absente, rien
ne bouge.")

P. 210 [93]. When there is too low a degree of tension, then too
great a number will be tapped ("si votre volonte ne les [les tables]
arrete pas au moment ou se termine le chiffre pense, elles
continueront indefiniment.")

P. 31 [93]. But too great concentration of attention will also
produce failure ("s'il n'arrivait ... de desirer trop fortement le
succes et de m'impatienter en cas de retard, je n'avais plus aucune
action sur la table.")

P. 36 [151]. If the proper mood ("entrain habituel") is wanting and
the tests are unsuccessful, it is best not to attempt some new and
difficult experiment, but to turn to some that are simpler and more
entertaining ("La table obeissait mal; les coups etaient frappes
mollement et comme a regret.... Alors nous avons pris un parti dont
nous nous sommes bien trouves; nous avons persevere, et persevere
gaiement; ... nous avons ecarte la pensee des tentatives nouvelles,
et insiste sur les operations aisees et amusantes. Apres un certain
temps les dispositions etaient changees, la table bondissait et
attendait a peine nos commandements.")

P. 199 [41, 90]. It is not necessary to enunciate the questions
aloud ("On est convenu que celui qui commanderait ne prononcerait
pas a haute voix le nombre de coups, mais se contenterait de les
penser, apres les avoir communiques a l'oreille de son voisin. Eh
bien! la table a obei. Il n'y a jamais eu la moindre erreur.")

P. 199 [64 ff.]. The large numbers are tapped more rapidly than the
small ones ("la table a indique notre age tel qu'il etait dans notre
esprit, se hatant meme de la maniere la plus comique lorsque le
nombre des coups a frapper etait un peu considerable.")

P. 210 [35 ff.]. Tests in which "procedure was without knowledge"
failed completely ("Les tables ne revelent pas ce qui n'est pas dans
la pensee et dans la volonte de l'experimentateur; quand on veut les
charger d'autre chose que d'obeir comme des membres, on arrive a des
erreurs continuelles.")

P. 28, 29, 217 [72]. When of two experimenters each tries to get the
horse to tap a different number, then that one who is the better
able to compel the animal's attention, will be the successful one.
("L'un veut faire prevaloire un chiffre pense plus considerable,
l'autre un chiffre pense moins considerable.... Eh bien: l'operateur
le plus puissant l'emporte." "Ainsi A est charge secretement de
faire frapper 25 coups, B est charge secretement de l'arreter a 18;
A l'emporte, et les 25 coups s'achevent.... On fait maintenant
l'inverse: B est charge secretement de faire frapper 13 coups; A est
charge secretement de l'arreter a 7; A l'emporte encore et le
chiffre 7 ne peut etre depasse.")]

The experience of a number of practical men, who have had much to do with horses and yet achieved but very modest success with Hans, goes to show that it is not always the lack of sufficient authoritativeness, mentioned under heading 1 that is the sole cause of failure, as has been claimed so often. That the horse was, to a certain degree, influenced by this element of authority is shown, however, by the following incident. A certain gentleman, when alone in the courtyard with Hans, received responses only so long as I (concealed in the barn) kept the barn-door open just a little, so that my presence could be known to the horse. As soon as I closed the door, Hans refused to respond to the gentleman. Those who possessed sufficient power of concentration and the requisite motor tendency--the two characteristics mentioned under 1 and 2 above,--were able to obtain responses from the horse without any previous practice. Practice merely effected a more economic distribution of attention, so that the larger numbers especially were more successful as a result (pages 68 and 89). Those who were lacking in either of the characteristics mentioned under 2 and 3 would not be aided even by the greatest amount of practice, as is shown by the case mentioned in Supplement III (page 255).--That many individuals were at first successful but were later unable to get any successful responses, is to be accounted for by the fact that the power of concentration, at first present, later rapidly disappeared. This temporary increase in the power of doing mental work was first investigated experimentally by Rivers and Kraepelin,[95] and was called by them "Antrieb" and aptly likened to the first pull of a team of horses in starting off. This, too, explains an experience which befell a number of the horse's visitors, who later described it to me. Wishing to utilize a momentary absence of Mr. von Osten, they excitedly put a hasty question to Hans, and with amazing regularity received correct responses.--Besides Mr. von Osten, Mr. Schillings and myself, not many were always able to induce Hans to bring the colored cloths or to execute the head movements. It was easy, on the other hand, to get him to nod. Therefore there was some truth in Mr. von Osten's assertion, that Hans would be unable to answer a difficult question if he had not previously indicated by means of a nod that he had grasped its import. Those who were not concentrating sufficiently, would not look into Hans's face, when he was expected to nod, and would not bend over, when Hans ought to begin tapping--such persons could not, therefore, since they did not induce Hans to nod, elicit the tapping. I, myself saw the "no" successfully elicited only in the case of Mr. von Osten, Mr. Schillings and Mr. Hahn; the "right" and "left" only in the case of the former two. It must remain uncertain whether this failure on the part of otherwise suitable persons to elicit the responses for "right" and "left" was due to their accompanying these ideas by movements of the eyes instead of by movements of the head, (page 106). For unfortunately it was not possible to make special tests to discover whether Hans reacted to isolated eye movements. There is, however, more than one reason why I would doubt this. Taken all in all, there were but few persons who were entirely representative of the type described (c. f. page 31)--they were those who are commonly characterized as being of a lively temperament and strongly impulsive. Thus Hans acquired a reputation for "Einkennigkeit", that is, he would accustom himself only to certain persons. Such a reputation was hard to reconcile with his much praised intelligence.

In closing, just a word on the influence of the public that was present. As was shown on page 69, the public in general did not influence the horse in his reactions. The effect upon the questioner, however, was unmistakable, and worked in a twofold manner. On the one hand the questioner's zeal was increased and with it the tension of concentration. On the other hand, it introduced an element of diversion, and attention was divided between the horse and the spectators, and thus concentration suffered. If the disturbing effect was slight, as in the case of Mr. von Osten, then the favorable influence exercised by the presence of the public outweighed the unfavorable. Mr. von Osten was, for that reason, often particularly successful when working in the presence of a large body of spectators. This was noted by many and was ascribed to the ambition of the horse. When, however, a person was easily diverted, as was Mr. Schillings, then the presence of the public had a less fortunate effect.

This, then, completes my explanation of the facts gleaned from observation and experimentation. It accomplishes all, I hope, that may be expected of an explanation. All the known achievements of the horse, all the successes and failures of the questioner, have been reduced to a single principle; no secondary hypothesis has been invoked, and but slight place has been given to the element of chance. Nevertheless, it may not be out of place to forestall two objections which might possibly be raised. First, some may assert that it was through our experimentation that the horse became mechanized and incapacitated as regards conceptual thinking; that formerly he really could solve arithmetical problems, and only later developed the very bad habit of depending upon the signs which I gave him. This objection is to be refuted in that I did not originate these signs, but first noted them in Mr. von Osten, himself, and in that Hans still works as faithfully as ever for Mr. von Osten. I have learned from many trustworthy witnesses that the horse still continues to give brilliant exhibitions of his "ability". If, on the other hand, anyone should assert that it was only with us that Hans reacted to movements, but that with his master he really thought and still thinks, then I must ask for proof. This latter argument is by no means very original. When Faraday in 1853 proved experimentally that "table-rapping" is the result of involuntary movements on the part of the participants standing about the table, the spiritualists asserted that his experiments had nothing in common with their own proceedings, because his subjects (who by the way, had been up to that time firm believers in table-rapping) probably did move the table, they said, while they (the spiritualists) do no such thing.[96]