CLEVER HANS

CLEVER HANS

(THE HORSE OF MR. VON OSTEN)

A CONTRIBUTION TO EXPERIMENTAL
ANIMAL AND HUMAN
PSYCHOLOGY

BY
OSKAR PFUNGST

WITH AN INTRODUCTION BY PROF. C. STUMPF, AND ONE ILLUSTRATION AND FIFTEEN FIGURES

TRANSLATED FROM THE GERMAN
BY
CARL L. RAHN
Fellow in Psychology in the University of Chicago

WITH A PREFATORY NOTE BY
JAMES R. ANGELL
Professor of Psychology in the University of Chicago

NEW YORK
HENRY HOLT AND COMPANY
1911

Copyright, 1911
BY
HENRY HOLT AND COMPANY

PREFATORY NOTE

[By James R. Angell]

The University of Chicago

It gives me great pleasure to accept the invitation of the publishers to write a word of introduction for Mr. Rahn's excellent translation of "Der Kluge Hans", a book which in the original has been but little known to American readers. The present wave of interest in animal life and behavior renders its appearance peculiarly appropriate.

No more remarkable tale of credulity founded on unconscious deceit was ever told, and were it offered as fiction, it would take high rank as a work of imagination. Being in reality a record of sober fact, it verges on the miraculous. After reading Mr. Pfungst's story one can quite understand how sedate and sober Germany was for months thrown into a turmoil of newspaper debate, which for intensity and range of feeling finds its only parallel in a heated political campaign. That the subject of the controversy was the alleged ability of a trained horse to solve complex arithmetical problems may excite gaiety and even derision, until one hears the details. Scientists and scholars of the highest eminence were drawn into the conflict, which has not yet wholly subsided, although the present report must be regarded as quite final in its verdict.

As for Hans himself, he has become the prototype of a host of less distinguished imitators representing every level of animal life, and when last heard from he was still entertaining mystified audiences by his accomplishments.

But the permanent worth of the book is not to be found in its record of popular excitement, interesting as that is. It is a document of the very first consequence in its revelation of the workings of the animal mind as disclosed in the horse. Animal lovers of all kinds, whether scientists or laymen, will find in it material of greatest value for the correct apprehension of animal behavior. Moreover, it affords an illuminating insight into the technique of experimental psychology in its study both of human and animal consciousness. Finally, it contains a number of highly suggestive observations bearing on certain aspects of telepathy and muscle-reading. All things considered, it may fairly be said that few scientific books appeal to so various a range of interests in so vital a way.

Readers who wish to inform themselves of all the personal circumstances in the case may best read the text just as it stands. Those who desire to get at the pith of the matter without reference to its historical settings, may be advised to omit the [Introduction] by Professor Stumpf of the University of Berlin, together with supplements [II], [III] and [IV].

CONTENTS

INTRODUCTION

[By C. Stumpf]

A horse that solves correctly problems in multiplication and division by means of tapping. Persons of unimpeachable honor, who in the master's absence have received responses, and assure us that in the process they have not made even the slightest sign. Thousands of spectators, horse-fanciers, trick-trainers of first rank, and not one of them during the course of many months' observations are able to discover any kind of regular signal.

That was the riddle. And its solution was found in the unintentional minimal movements of the horse's questioner.

Simple though it may seem, the history of the solution is nevertheless quite complex, and one of the important incidents in it is the appearance of the zoölogist and African traveler, Schillings, upon the scene, and then there is the report of the so-called Hans-Commission of September 12, 1904. And finally there is the scientific investigation, the results of which were published in my report of December 9, 1904.

After a cursory inspection during the month of February, I again called upon Mr. von Osten in July, and asked him to explain to Professor Schumann and me just what method he had used in instructing the horse. We hoped in this way to gain a clue to the mechanism of Hans's feats. The most essential parts of the information thus gleaned are summarized in [Supplement I]. Mr. Schillings came into the courtyard for the first time about the middle of July. He came as skeptical as everyone else. But after he, himself, had received correct responses, he too became convinced, and devoted much of his time to exhibiting the horse, and daily brought new guests. To be perfectly frank, at the time this seemed to us a disturbing factor in the investigation, but now we see that his intervention was a link in the chain of events which finally led to an explanation. For it was through him that the fact was established beyond cavil, that the horse was able to respond to strangers in the master's absence. Heretofore, this had been noted only in isolated cases. Since it could not be assumed that a well-known investigator should take it upon himself to mislead the public by intentionally giving signs, the case necessarily from that time on appeared in the eyes of others in a light quite different from that in which ordinary circus-tricks would appear, to which it bore such a striking external resemblance. No matter how this state of affairs may have arisen in the course of years, no matter how it might eventually be explained,—the quality of the extraordinary would necessarily attach itself to this particular case, as it did.

Of course, to many persons in the interested public the result was merely that Schillings, also, was placed in the category of deceivers. On the other hand there were reputable scientists who could not dispose of the matter in that fashion, and these now openly took their stand with Schillings and declared that they believed in the horse's ability to think. Zoölogists especially, saw in von Osten's results evidence of the essential similarity between the human and the animal mind, which doctrine has been coming more and more into favor since the time of Darwin. Educators were disposed to be convinced, on account of the clever systematic method of instruction which had been used and which had not, till then, been applied in the education of a horse. In addition, there were many details which, it seemed, could not be explained in any other way. So far as I myself was concerned, I was ready to change my views with regard to the nature of animal consciousness, as soon as a careful examination would show that nothing else would explain the facts, except the assumption of the presence of conceptual thinking. I had thought out the process hypothetically, i. e., how one might conceive of the rise of number concepts and arithmetical calculation along the peculiar lines which had been followed in Hans's education, and on the basis of the assumption that the beginnings of conceptual thinking are present in animals. Also, I had too much faith in human nature to fear lest nothing peculiarly human should remain after the art of handling numbers should be shown to be common property with the lower forms. But under no circumstances would I have undertaken to make a public statement in favor of any particular view in this extraordinary case, before a thorough investigation, in accordance with scientific principles, had been made. I expressed this sentiment at the time, and recommended the appointment of an investigating commission (in the "Tag" of September 3, 1904).

The purpose of this commission was misunderstood, and therefore many were disappointed with the report which it published, ([Supplement II]). Some had been expecting a positive conclusive explanation; the commission recommended further investigation. Some had asked for a solution of the question whether or not the horse was able to think; the commission maintained neither the one, nor the other. Some had indicated as the main condition of a satisfactory investigation, that both Mr. von Osten and Mr. Schillings be excluded from the tests; this was not done.

But the commission—which, by the way, did not give itself this name, since it had been delegated by no one—undoubtedly had the right to formulate its problem as it saw fit, and this was carefully expressed at the beginning of its report as follows: "The undersigned came together for the purpose of investigating the question whether or not there is involved in the feats of the horse of Mr. von Osten anything of the nature of tricks, that is, intentional influence or aid on the part of the questioner." It was this preliminary question, and not whether or not the horse could think, which the commission intended to answer. They proposed to act as a sort of court of honor for the two gentlemen who had been attacked. It is only in this light that even the raison d'être of this body can be understood; for a scientific commission composed of thirteen men, possessed of varying degrees of scientific preparation, would have been an absurd travesty, and it will readily be seen why the two men, who had been attacked, should not be excluded, since it was they, and primarily Mr. von Osten, upon whom the observations were to be made.

To be sure the commission did go one step beyond that which it had proposed to itself, since it added that it believed that unintentional signs of the kind which are at present familiar, were also excluded. This led many to the unwarranted conclusion that the commission had declared that Hans was able to think. Whereas the thing which might have been logically suggested was that instead of the assumption of the presence of independent thinking, the commission may have had in mind unintentional signs of a kind hitherto unknown. I explained this to a reporter of the "Frankfurter Zeitung" (Mr. A. Gold), who had come to me for information, and in his article he made this hypothesis appear as the most probable one.[A] Certain statements of the circus-manager Busch, who speaks of a 'connection' of some sort, go to show that other members of the commission held to the view just stated.

But how did it come to pass that the commission should deny completely the presence of intentional signals, while, as regards the unintended, it excluded only those which were of the known sort? The report clearly shows that the decision as to the absence of voluntary signals was based not merely upon the fact that no such signals had been detected by the most expert observers, but also upon the character of the two men who exhibited the horse, upon their behavior during the entire period, and upon the method of instruction which Mr. von Osten had employed. In the case of unintentional signs, on the other hand, one had to deal with the fact with which physiologists and experimental psychologists are especially familiar, viz., that our conscious states, without our willing it—indeed, even in spite of us—are accompanied by bodily changes which very often can be detected only by the use of extremely fine graphic methods. The following is a more general instance: every mother, who detects the lie or divines the wish in the eyes of the child, knows that there are characteristic changes of facial expression, which are, nevertheless, very difficult of definition.[B]

The commission did not even maintain or believe that unintentional signs within the realm of the senses known to us, were to be excluded. Professor Nagel and I would never have subscribed to any such conclusion. The sentence in question, therefore, could only be interpreted as follows: that signals of the kind that are used intentionally in the training of horses, could not have occurred even as unintended signs, for otherwise Mr. Busch would have detected them. And in order to be observed by him it was immaterial whether they were given purposely or not. The same signs, therefore, which as a result of his observations were declared not to be present, could not be assumed to be involved as unintentional.

For my part I am ready to confess that at this time I did not expect to find the involuntary signals, if any such were involved, in the form of movements. I had in mind rather some sort of nasal whisper such as had been invoked by the Danish psychologist A. Lehmann, in order to explain certain cases of so-called telepathy. I could not believe that a horse could perceive movements which escaped the sharp eyes of the circus-manager. To be sure, extremely slight movements may still be perceived after objects at rest have become imperceptible. But one would hardly expect this feat on the part of an animal, who was so deficient in keenness of vision, as we have been led, by those of presumably expert knowledge, to believe of the horse,—one would expect it all the less because Mr. von Osten and Mr. Schillings would move hither and thither in most irregular fashion while the horse was going through his tapping, and would therefore make the perception of minute movements all the more difficult.

Nor was there anything in the exhibitions given at the same time in a Berlin vaudeville by the mare "Rosa," which might have shattered this belief. For, in the case of this rival of Hans, the movements involved were comparatively coarse. The closing signal consisted in bending forward on the part of the one exhibiting the mare, while up to that point he had stood bolt upright. Most persons were not aware of this, because this change in posture cannot be noticed from the front. I happened to sit to the side and caught the movement every time. It was the same that was noted by Dr. Miessner, another member of the commission, (see [page 256]), but concerning which he did not give me a more complete account. Later I learned through Professor Th. W. Engelmann that the very same movement was employed not long ago, for giving signals to a dog exhibited at Utrecht. This particular movement is very well adapted to commercial purposes, since the spectator always tries to view the performance from a point as nearly in front of the animal and its master as possible, thus making the detection of the trick all the more difficult.

The details of the various experiments made by this commission are given in an excerpt from the records kept by Dr. von Hornbostel, which I showed to a small group of persons a few days after the 12th of September ([Supplement III]). At that time none of the particulars was published, because the commission wished to wait until some positive statement might be made. The public was merely to be assured that a group of reputable men, from different spheres of life, who could have no purpose in hazarding their reputation, believed that the case was one worthy of careful investigation.

I left Berlin on September 17th and did not return until October 3d. In the meantime Mr. Schillings continued the investigation, and was assisted in part by Mr. Oskar Pfungst, one of my co-workers at the Psychological Institute. For the first time a number of tests were now made in which neither the questioner, nor any of those present knew the answer to the problem. Such tests naturally were the first steps toward a positive investigation. The results were such that Mr. Schillings was led to replace his hypothesis of independent conceptual thinking by one of some kind of suggestion. In this he was strengthened somewhat by having noted the fact that in his questions which he put to the horse, he might proceed as far as to ask the impossible. He has always been ready to offer himself in the tests which have been undertaken since then.

On October 13, 1904, together with the two gentlemen mentioned in the beginning of my report, I began my more detailed investigation, and finished on November 29. We worked for several hours on the average of four times each week. I take this opportunity of giving expression of the recognition which is due to the two gentlemen. They were ready to go to the courtyard in all kinds of weather, at times they went without me, and they always patiently discussed the order and method of the experiments and the results. Dr. von Hornbostel had the important task of keeping the records, and Mr. Pfungst undertook the conduct of the experiments. It was he, who, soon after the blinder-tests disclosed the necessary presence of visual signs, discovered the nature of these signs. Without him we might have shown the horse to be dependent upon visual stimuli in general, but we never would have been able to gain that mass of detail, which makes the case valuable for human psychology. But I am tempted to praise not merely his patience and skill, but also his courage. For we must not believe that Mr. von Osten's horse was a "perfectly gentle" animal. If he stood untied and happened to be excited by some sudden occurrence, he would make that courtyard an unsafe place, and both Mr. Schillings and Mr. Pfungst suffered from more than one bite. In this connection I would also express my obligations to Count Otto zu Castell-Rüdenhausen, for his frequent intercession on our behalf with the owner of the horse, and for his many evidences of good-will and helpfulness.

After the publication of this report ([Supplement IV]), there was still some further discussion of the case in societies of various kinds and in the press, but no important objections were raised. A hippologist thought that men of his calling should have been consulted, a telepathist believed that telepathists should have been called in. There was also some further talk of suggestion, will-transference, thought-reading and the occult, but no attempt was made to elucidate these vague terms with reference to their application to the case in hand. Others adhered to the old cry of "fraud," for a share of which Mr. Pfungst now fell heir. There were a few who felt it incumbent upon themselves to preserve their 'priority,' and therefore stated with a show of satisfaction that I had finally 'confessed' myself to hold their respective points of view. As if there were anything like "confessions" in science! As if mere affirmations, even though sealed and deposited in treasure vaults, had any value with reference to a case in which every manner of supposition had been advanced in lieu of explanation. Why did they wait so long, if they had convincing proof for their position?

And finally there were disappointed Darwinists who expressed fear lest ecclesiastical and reactionary points of view should derive favorable material from the conclusions arrived at in my report. Needless fear. For lovers of truth it must always remain a matter of inconsequence whether anyone is pleased or displeased with the truth, and whether it is enunciated by Aristotle or Haeckel.

Mr. von Osten, however, continued to exhibit Hans, and is probably doing so still, but in what frame of mind, I dare not judge. The spectators continue to look on, they are doubly alert to catch movements, and many of them have learned from Mr. Schillings what kind of movements they are to expect. But these "initiated" ones regularly return and declare that there is nothing in the movements and that they simply could not discover any aids given to the horse. Nothing can so well show how difficult the case is, and how great the need of a thorough exposition of the whole matter, than the account given in the following pages of Mr. Pfungst. Its publication has been delayed on account of the additional tests made in the laboratory, but we have reason to suppose that through these additional tests the work has gained in permanent value. Experimental psychologists will perhaps be greatly interested in the graphic registration of the minute involuntary movements which accompany the thought process, and in the artificial association of a given involuntary movement with a given idea. Likewise the tests on sense-perception in horses, which have led to essential changes in hitherto current views, and the critical review of the comprehensive literature on similar achievements of other animals, will be welcomed by many.

Before closing these introductory remarks, I would make one more statement concerning Mr. von Osten. The reader will notice that the judgment passed upon him in this treatise is placed at the end, whereas in the report of the commission it came first. This was brought about by the change that was made in the way of stating the problem. Then the question discussed was whether 'tricks' were involved; now the question is: What is the mechanism of the process? The question of the good faith of the master was taken up once more only because the facts that were brought to light by the later experimentation seemingly brought forward new grounds for distrust. But by placing this discussion toward the end of our report we wished to indicate that everything that is said of the present status of facts, is quite independent of the view taken concerning Mr. von Osten. Even assuming that the horse had been purposely trained by him to respond to this kind of signal, the case would still deserve a place in the annals of science. For visual signs, planned and practiced so that they could not only be more readily perceived by the animal than by man, but could be transferred from their inventor to others without any betrayal of the secret,—this would be an extraordinary invention, and Mr. von Osten would then be a fraud, but also a genius of first rank.

In truth he probably was neither, but I was brief in my report, for otherwise I would have been obliged to go into more detail than the case warranted. And a judgment passed upon a human personality is quite a different matter from a judgment upon a horse. If it is unscientific to make unqualified statements concerning a horse after the performance of only a few experimental tests, it is certainly an unwarranted thing to pass a moral judgment upon a man upon the basis of meagre material. Anyone who would assume the rôle of judge should bear in mind that here too we have more than a hundredfold the material which they could bring forward, and among it some which, if taken alone, would be more unfavorable than any that they had. But here all things should be weighed together, and not in isolation. A former instructor of mathematics in a German gymnasium, a passionate horseman and hunter, extremely patient and at the same time highly irrascible, liberal in permitting the use of the horse for days at a time and again tyrannical in the insistence upon foolish conditions, clever in his method of instruction and yet at the same time possessing not even the slightest notion of the most elementary conditions of scientific procedure,—all this, and more, goes to make up the man. He is fanatic in his conviction, he has an eccentric mind which is crammed full of theories from the phrenology of Gall to the belief that the horse is capable of inner speech and thereby enunciates inwardly the number as it proceeds with the tapping. From theories such as these, and on the basis of all sorts of imagined emotional tendencies in the horse, he also managed to formulate an explanation for the failure of the tests in which none of the persons present knew the answer to the problem given the horse, and also for the failure of those tests in which the large blinders were applied. And he would often interfere with or hinder other tests which, according to his point of view, were likely to lead us astray. And yet, when the first tests with the blinders did turn out as unmistakably sheer failures, there was such genuine surprise, such tragi-comic rage directed against the horse, that we finally believed that his views in the matter would be changed beyond a doubt. "The gentlemen must admit," he said at the time, "that after seeing the objective success of my efforts at instruction, I was warranted in my belief in the horse's power of independent thought." Nevertheless, upon the following day he was as ardent an exponent of the belief in the horse's intelligence as he ever had been.

And finally, after I could no longer keep from him the results of our investigation, I received a letter from him in which he forbade further experimentation with the horse. The purpose of our inquiries, he said, had been to corroborate his theories. On account of his withdrawal of the horse a few experimental series unfortunately could not be completed, but happily the major portion of our task had been accomplished.

THE HORSE OF MR. VON OSTEN

CHAPTER I

THE PROBLEM OF ANIMAL CONSCIOUSNESS AND "CLEVER HANS"

If we would appreciate the interest that has been aroused everywhere by the wonderful horse solving arithmetical problems, we must first consider briefly the present state of the problem of animal consciousness.[C] Animal consciousness cannot be directly gotten at, and the psychologist must therefore seek to appreciate it on the basis of the animal's behavior and with the assistance of conceptions borrowed from human psychology. Hence it is that animal psychology rests upon uncertain foundations with the result that the fundamental principles have been repeatedly questioned and agreement has not yet been attained. The most important of these questions is, "Does the animal possess consciousness, and is it like the human consciousness?" Comparative psychologists divide into three groups on this question.

The one group allows consciousness to the lower forms, but emphasizes the assertion that between the animal and the human consciousness there is an impassable gap. The animal may have sensations and memory-images of sensations which may become associated in manifold combinations. Both sensations and memory images are believed to be accompanied by conditions of pleasure and of pain (so-called sensuous feelings), and these in turn, become the mainsprings of desire. The possession of memory gives the power of learning through experience. But with this, the inventory of the content of animal consciousness is exhausted. The ability to form concepts[D] and with their aid to make judgments and draw conclusions is denied the lower forms. All the higher intellectual, æsthetic and moral feelings, as well as volition guided by motives, are also denied. Among the ancients this view was held by Aristotle and the Stoics; and following them it was taught by the Christian Church. It pervaded all mediæval philosophy, which grew out of the teachings of Aristotle and the Church. It is this philosophy, in the form of Neo-Thomism, which still obtains in the Catholic world.

During the 17th century, even though temporarily, another conception of the consciousness of lower forms came to prevail and was introduced by Descartes, the "Father" of modern philosophy. Far more radical than the earlier conception, it denied to animals not only the power of abstract thought, but every form of psychic life whatever, and reduced the lower form to a machine, which automatically reacted upon external stimuli. This daring view, however, prevailed for only a comparatively short period; but owing to the opposition which it aroused, it gave a tremendous impetus to the study of animal consciousness. Most of the great philosophers following Descartes, such as Locke, Leibniz, Kant, and Schopenhauer, however greatly they may have differed in other points, in this one returned to the Aristotelian point of view.

A third belief avers that animal and human consciousness do not differ in essentials, but only in degree. This conclusion is regularly arrived at by those who regard so-called abstract thought itself, as simply a play of individual sensations and sensation-images, as did the French and British associationists (Condillac and the Mills). The superiority of man accordingly consisted in his ability to form more intricate ideational complexes. Again, this conception of the essential similarity of the human and the animal psyche has also always been arrived at by the materialists (from Epicurus to C. Vogt and Büchner) who impute reason to the animal form as well as to man. The same position is, furthermore, taken by the evolutionists, including those who do not subscribe to the doctrines of materialism. It has almost become dogma with them that there exists an unbroken chain of psychic life from the lowest protozoa to man. Haeckel, preëminently, though not always convincingly, sought to establish such a graded series and thus to bridge the chasm between the human and the animal consciousness.

Two tendencies, therefore, are discernible in animal psychology. The one seeks to remove the animal psyche farther away from the human, the other tries to bring the two closer together. It is undoubtedly true that many acts of the lower forms reveal nothing of the nature of conceptual thinking. But that others might thus be interpreted cannot be denied. But need they be thus interpreted?—There lies the dispute. A single incontrovertible fact which would fulfil this demand, [i.e., proof of conceptual thinking], would, at a stroke, decide the question in favor of those who ascribe the power of thought to the lower forms.

At last the thing so long sought for, was apparently found: A horse that could solve arithmetical problems—an animal which, thanks to long training, mastered not merely rudiments, but seemingly arrived at a power of abstract thought and which surpassed, by far, the highest expectations of the greatest enthusiast.

And now what was it that this wonderful horse could do? The reader may accompany us to an exhibition which was given daily before a select company at about the noon hour in a paved courtyard surrounded by high apartment houses in the northern part of Berlin. No fee was ever taken. The visitor might walk about freely and if he wished, might closely approach the horse and its master, a man between sixty and seventy years of age. His white head was covered with a black, slouch hat. To his left the stately animal, a Russian trotting horse, stood like a docile pupil, managed not by means of the whip, but by gentle encouragement and frequent reward of bread or carrots. He would answer correctly, nearly all of the questions which were put to him in German. If he understood a question, he immediately indicated this by a nod of the head; if he failed to grasp its import, he communicated the fact by a shake of the head. We were told that the questioner had to confine himself to a certain vocabulary, but this was comparatively rich and the horse widened its scope daily without special instruction, but by simple contact with his environment. His master, to be sure, was usually present whenever questions were put to the horse by others, but in the course of time, he gradually responded to a greater and greater number of persons. Even though Hans did not appear as willing and reliable in the case of strangers as in the case of his own master, this might easily be explained by the lack of authoritativeness on their part and of affection on the part of Hans, who for the last four years had had intercourse only with his master.

Our intelligent horse was unable to speak, to be sure. His chief mode of expression was tapping with his right forefoot. A good deal was also expressed by means of movements of the head. Thus "yes" was expressed by a nod, "no" by a deliberate movement from side to side; and "upward," "upper," "downward," "right," "left," were indicated by turning the head in these directions. In this he showed an astonishing ability to put himself in the place of his visitors. Upon being asked which arm was raised by a certain gentleman opposite him, Hans promptly answered by a movement to the right, even though seen from his own side, it would appear to be the left. Hans would also walk toward the persons or things that he was asked to point out, and he would bring from a row of colored cloths, the piece of the particular color demanded. Taking into account his limited means of expression, his master had translated a large number of concepts into numbers; e. g.:—the letters of the alphabet, the tones of the scale, and the names of the playing cards were indicated by taps. In the case of playing cards one tap meant "ace," two taps "king," three "queen," etc.

Let us turn now to some of his specific accomplishments. He had, apparently, completely mastered the cardinal numbers from 1 to 100 and the ordinals to 10, at least. Upon request he would count objects of all sorts, the persons present, even to distinctions of sex. Then hats, umbrellas, and eyeglasses. Even the mechanical activity of tapping seemed to reveal a measure of intelligence. Small numbers were given with a slow tapping of the right foot. With larger numbers he would increase his speed, and would often tap very rapidly right from the start, so that one might have gained the impression that knowing that he had a large number to tap, he desired to hasten the monotonous activity. After the final tap, he would return his right foot—which he used in his counting—to its original position, or he would make the final count with a very energetic tap of the left foot,—to underscore it, as it were. "Zero" was expressed by a shake of the head.

But Hans could not only count, he could also solve problems in arithmetic. The four fundamental processes were entirely familiar to him. Common fractions he changed to decimals, and

vice versa; he could solve problems in mensuration—and all with such ease that it was difficult to follow him if one had become somewhat rusty in these branches. The following problems are illustrations of the kind he solved.[E] "How much is 2/5 plus ½?" Answer: 9/10. (In the case of all fractions Hans would first tap the numerator, then the denominator; in this case, therefore, first 9, then 10). Or again: "I have a number in mind. I subtract 9, and have 3 as a remainder. What is the number I had in mind?"—12. "What are the factors of 28?"—Thereupon Hans tapped consecutively 2, 4, 7, 14, 28. "In the number 365287149 I place a decimal point after the 8. How many are there now in the hundreds place?"—5. "How many in the ten thousandths place?"—9. It will be noticed, therefore, that he was able to operate with numbers far exceeding 100, indeed he could manipulate those of six places. We were told that this, however, was no longer arithmetical computation in the true sense of the term; Hans merely knew after the analogy of 10 and 100 that the thousands take the fourth place, the ten-thousands the fifth, etc. If an error entered into Hans' answer, he could nearly always correct it immediately upon being asked: "By how many units did you go wrong?"

Hans, furthermore, was able to read the German readily, whether written or printed. Mr. von Osten, however, taught him only the small letters, not the capitals. If a series of placards with written words were placed before the horse, he could step up and point with his nose to any of the words required of him. He could even spell some of the words. This was done by the aid of a table devised by Mr. von Osten, in which every letter of the alphabet, as well as a number of diphthongs had an appropriate place which the horse could designate by means of a pair of numbers. Thus in the fifth horizontal row "s" had first place; "sch" second, "ss," third, etc.; so that the horse would indicate the letter "s" by treading first 5, then 1, "sch," by 5 and 2, "ss" by 5 and 3. Upon being asked "What is this woman holding in her hand?" Hans spelled without hesitation: 3, 2; 4, 6; 3, 7; i. e., "Schirm" (parasol). At another time a picture of a horse standing at a manger was shown him and he was asked, "What does this represent?" He promptly spelled "Pferd" (horse) and then "Krippe" (manger).

He, moreover, gave evidence of an excellent memory. In passing we might also mention that he knew the value of all the German coins. But most astonishing of all was the following: Hans carried the entire yearly calendar in his head; he could give you not only the date for each day without having been previously taught anew, but he could give you the date of any day you might mention. He could also answer such inquiries as this: "If the eighth day of a month comes on Tuesday, what is the date for the following Friday?" He could tell the time to the minute by a watch and could answer off-hand the question, "Between what figures is the small hand of a watch at 5 minutes after half-past seven?" or, "How many minutes has the large hand to travel between seven minutes after a quarter past the hour, and three quarters past?" Tasks that were given him but once would be repeated correctly upon request. The sentence: "Brücke und Weg sind vom Feinde besetzt" (The bridge and the road are held by the enemy), was given to Hans one day and upon the following day he tapped consecutively the 58 numbers which were necessary for a correct response. He recognized persons after having seen them but once—yes, even their photographs taken in previous years and bearing but slight resemblance.

A corresponding high degree of sensory activity seemed to accompany these astonishing feats of memory and reason. Although the horse is not usually credited with a very keen sense of vision, Hans was able to count the windows of distant houses and the street urchins climbing about on neighboring roofs. He had an ear for the most subtle nuances of the voice. He caught every word,—no matter how softly it was spoken—so that we were not allowed to whisper the answer to a problem, even when standing at a distance of several yards, since it would be equivalent—so Mr. von Osten declared—to giving the result to the horse.

Musical ability also comes into the category of Hans' accomplishments. He possessed, not only an absolute tone consciousness—a gift granted to few of us in the human world—which enabled him to recognize a note sounded or sung to him as c, d, etc. (within the once accented scale of c-major), but also an infallible feeling for intervals, and could therefore determine whether two tones, sounded simultaneously, composed a third or fifth, etc. Without difficulty he analyzed compound clangs into their components; he indicated their agreeableness or disagreeableness and could inform us which tones must be eliminated to make consonance out of dissonance. C, d and e were given simultaneously and Hans was asked: "Does that sound pleasant?" He shook his head. "What tone must be omitted to make it pleasant?" Hans trod twice—indicating tone "d." When the seventh chord, d-f-a-c, was sounded, he shook his head disapprovingly. He evidently was old-fashioned in his musical tastes and not agreeably disposed toward modern music, so he indicated by tapping that the seventh, c, would have to be eliminated; thus changing the seventh chord to a minor chord in order to obtain harmony. When asked what tones might not be given simultaneously with the fourth and sixth, Hans indicated consecutively the third, fifth and seventh; that the first might be added, he was ready to admit. Finally, he was familiar with not less than thirteen melodies and their time.

Not only in the high degree of development of the senses and the intellect, but also in that of the feeling and the will, did Hans possess a decided individuality. Being of a high-strung and nervous temperament and governed by moods, he evinced strong likes and dislikes, and frequently displayed an annoying stubbornness,—a fact often dwelt upon by Mr. von Osten. He had never felt the whip, and therefore often persisted in wilfully answering the simplest questions incorrectly and a moment later would solve, with the greatest ease, some of the most difficult problems. Whenever any one asked a question without himself knowing the answer, Hans would indulge in all sorts of sport at the questioner's expense. We were told that the sensitive animal could easily perceive the questioner's ignorance and would therefore lose confidence in, and respect for, him. It was felt to be desirable, however, to have just such cases with correct responses. Often, too, Hans would persist in giving what seemed an incorrect reply, but which was later discovered to be correct. On the other hand it was useless to try to get answers upon topics of which he knew nothing. Thus he ignored questions put in French or Latin and became fidgety, thereby showing the genuineness of his achievements; but upon topics with which he was familiar he could not be led astray. Indeed, there was nothing but language lacking to make him almost human and the intelligent animal was declared by experienced educators to be at about the stage of development of a child of 13 or 14 years.

This wonderful horse, which in the opinion of its friends was the means of deciding in the affirmative the old, old, question of the rationality of the lower forms and thus changing radically the existing Weltanschauung, aroused world-wide interest. A flood of articles appeared in the newspapers and magazines, two monograph[1,] [2] attempts at explanation were devoted to him.[F] He was made the subject of popular couplets, and his name was sung on the vaudeville stage. He appeared upon picture post-cards and upon liquor labels, and his popularity was shown by his reincarnation in the form of children's playthings. Many personages of note who had seen the horse's exhibitions, declared, some of them in public statements, that they were now convinced. Among these, besides Mr. Schillings, were naturalists of note; e. g.: the African explorer Prof. G. Schweinfurth, Dr. Heinroth and Dr. Schäff, the director of the zoological garden in Hanover; there were likewise horse-fanciers of first-rank, such as General Zobel, and the well-known hippological writer Major R. Schoenbeck. Again, the well-known zoölogist, K. Möbius, writing in the "National-zeitung" declared he was convinced of the horse's power to count and to solve arithmetical problems. He also said that he believed the horse's memory and acute power of sense-discrimination to be at the root of the matter. Those who gleaned all their knowledge of the horse from newspaper reading were satisfied to arrest judgment, or, on the other hand, became indignant at the supposed imposition on the part of the gentleman of leisure and at the gullibility of the public. Some would of course attempt explanations on the basis of older facts. Here we have two points of view.

Some tried to explain the whole thing on the basis of purely mechanical memory and would thus allow the title "learned" but not "intelligent" Hans. If, for instance, he was able to indicate the component of a clang of three tones, it was not because he had the power to analyze the tone-complex, but because he was able to see the stops of the harmonica and was accustomed to give one tap for every stop which was closed. If he was able to tell time by the watch, it was not because he read it, but because he was always asked at the same hour of the day (which, of course, was contrary to fact) and because he had learned by heart the necessary number of taps. They also said that his manifold arithmetical achievements were merely the expression of a remarkable memory; that in the animal brain, lying fallow for centuries, there was stored up a tremendous amount of energy, which here had been suddenly released. They justified their point by calling to mind, in this connection, the wonderful memory of primitive races. The authors of the two monographs already mentioned, Zell and Freund, adopted this 'mnemotechnic' interpretation, and the latter considered that he had disposed definitely of the problem in designating the horse—a "four-legged computing machine."

Another group would not even allow Hans the glory of a wonderful memory. He knew nothing. Rather was he to be regarded as a stupid Hans, and totally dependent upon signs or helps given by his master. Only a very few believed, however, that such signs—the nature of which was quite unknown or regarding which only vague unsubstantiated suppositions were advanced—were given unintentionally. Most of the critics openly averred that we here had to do with intentional control, in other words, with tricks. But not only did stupid orthodoxy dispose of the matter in this way, but also the enlightened, who believe everything unusual to be contrary to reason. They put the Hans problem on a level with spiritualism, and were convinced that if the veil were removed a crass imposition would be revealed. Professional trainers who regarded themselves as well informed did not hesitate to give expression to this same view, even though they had observed Hans inadequately or not at all.

The defenders of this second point of view were not at a loss to point out the signs supposed to be given to Hans. One of these believed he had discovered the primary means for giving these signs in the slouch hat of Mr. von Osten. It was no accident, they said, that Mr. Schillings wore a slouch hat when he experimented with the horse. It is sufficient to note that Mr. Schillings was usually bare-headed or wore only a cap when he tested the horse. Another accused, in like fashion, the long coat of the experimenter; a third, who "had had opportunity to observe Hans on several occasions," declared with equal certainty that the cue lay in the movements of the hand as it was thrust into the pocket filled with carrots. One circus-star declared, that the trick lay in eye movements, another such star declared it lay in the movements of the hand. A sixth discovered that the signs were "manifold" and adds, "to be sure, the trainer must have a fund of such signs in order to prevent embarrassment." Such a hypothesis is itself, it would seem, one of embarrassment. On the other hand, there were many first-class observers who vainly tried to discover regularly recurring signs; among them the only professional trainer,—who had devoted any satisfactory length of time to the horse and had also sought diligently for the signs in question—said, "I was fully convinced that I would be able to explain the problem in this way, but I was mistaken." The president of the "Internationale Artisten Genossenschaft," a person who knew all the usual means of control in trick performances, went over to the other side as a result of his observations.

There were others who sought for auditory signs. The opinion was expressed that "Hans was unable to answer the simplest question such as 'What is two plus three?' whenever the questioner's tone of voice differed from that of the master's." Another put chief stress upon the changing inflection; furthermore, a "high degree of auditory sensitivity" was often offered in explanation.

The sense of smell was also made to bear some burdens. With its help, for instance, Hans was believed to be able to recognize the photograph of some one present, supposing, of course, that the person had carried the picture about with him, thus allowing it to be impregnated with his peculiar personal odor. One even suggested that the heat radiating from the questioner's body and the electric stimulus conducted underground to Hans's foot were sufficient explanation for his remarkable feats.

Even the so-called N-rays, of one-day fame, which were supposed to radiate from the human brain when in activity, were offered as a solution. A similar thing may have been in the mind of the "natural philosopher" who even after the publication of the December report, wrote as follows in one of the journals: "On the basis of most careful control, I have come to the conclusion, that the brain of the horse receives the thought-waves which radiate from the brain of his master; for mental work is, according to the judgment of science, physical work." Of the same character are the explanations of two others, one of whom declares that Hans was acting "under the magnetic influence of man", while the other declared that "hypnotic suggestion is involved", and, ignoring attested facts, tells us that, "The horse can execute the commands of another only when the master, with whom it is 'en rapport', wills that it shall obey." We may close the catalogue of explanations with one more, which, in spite of its vagueness, found many defenders, viz: suggestion. Without defining this conception more specifically and without the slightest notion of the peculiar difficulties which it involves (L. Loewenfeld in his "Handbuch des Hypnotismus" [Wiesbaden, 1901, pp. 35ff.] cites twenty different definitions of the term given by as many authors) a critic writes: "The astounding phenomenon of an animal apparently possessing human reason is to be attributed solely to suggestion". Having referred to a dog trained for the vaudeville-stage, the gentleman concludes that, "our intelligent horse, as well as the dog, is simply of fine nervous organization and hence highly susceptible to suggestions".

What was to be done, with this mass of conflicting explanations? Everyone considered his own opinion the only correct one, without, however, being able to convince anyone else. The need here was not simple affirmation, but proof.

FOOTNOTES:

[A] "Frankfurter Zeitung" of September 22, 1904: "Concerning the question whether the horse was given some sort of aid, Professor Stumpf expressed himself freely. He said: 'We were careful to state in our report that the intentional use of the (actual) means of training, on the part of the horse's teacher, is out of the question, ... nor are there involved any of the known kinds of unconscious, involuntary aids. Our task was completed after we had ascertained that no tricks or aids of the traditional sort were being employed'." After some remarks on unconscious habituation and self-training on the part of animals, the writer arrives at the conclusion that "the horse of Mr. von Osten has been educated by its master in the most round-about way, in accordance with a method suited for the development of human reasoning powers, hence in all good faith, to give correct responses by means of tapping with the foot. But what the horse really learned by this wearisome process was something quite different, something that was more in accord with his natural capacities,—he learned to discover by purely sensory aids which are so near the threshold that they are imperceptible for us and even for the teacher, when he is expected to tap with his foot and when he is to come to rest."

[B] "From the productions of the 'thought-readers' we see how slight and seemingly insignificant the unconscious movements may be, which serve as signs for a sensitive re-agent. But in this case no contact is necessary. There would have to be some sort of visible or audible expression on the part of the questioner. No proof for this has as yet been advanced."

How any one possessing the power of logical thought could possibly infer from these words of mine (published in the above-mentioned article in the "Tag"), that I denied the possibility of the occurrence of visual signs, is to me incomprehensible. What I did deny, and still deny, is that up to that time any had been proven to occur.

[C] Since the present treatise is intended for the larger public, this brief resumé will probably be welcome to many.

[D] Ideas are copies of former sensations, feelings and other psychic experiences and retain also the accidental signs which belonged to those earlier experiences. They are images in the concrete, such as the memory of a certain horse in a certain definite situation ... say a well fed, long-tailed one standing at a manger. A concept, on the other hand, is a mental construct which has its rise in ideas, or memory-images, in that their essential characteristics are abstracted. For this reason the concept has not a definite image-content. (Thus the thought of "horse" in general, is a concept. Not so the thought of a certain individual horse,——that is an idea, with a definite image-content.)

[E] All examples mentioned are cited from extant works of various observers.

[F] The works referred to in the text are to be found listed on [pages 267 ff.]

CHAPTER II

EXPERIMENTS AND OBSERVATIONS

A. Experimental Conditions

The observations on the horse under ordinary conditions would have been quite insufficient for arriving at a decision as to the tenability of the several possible explanations. For this purpose experimentation with controlled conditions was necessary.

It was necessary, first, that the place in which the experiments were performed should be guarded against sources of error and interruptions. Several difficulties stood in the way of the removal of the horse to a more convenient place. Therefore, a large canvas tent was erected within the courtyard of Mr. von Osten. This afforded the necessary isolation without hindering the free movements of the horse. After the essential part of the experiment had been completed and the problem had been practically solved, experimentation was sometimes conducted in the open courtyard. A number of the experiments were also performed in the horse's stall.

The choice of proper persons to experiment with the horse required careful consideration. In so far as observations were to be made upon the questioner, Mr. von Osten was of course indispensable. But to obviate every objection he, as well as Mr. Schillings, had to be excluded from the greater part of the experiments, and other persons had to be selected who could learn to handle the horse. Now one would have thought that the horse would respond to any moderately efficient examiner. But as a matter of fact it was found that the horse would not react at all in the case of the greater number of persons. Again, in the case of others he would respond once or twice, but would then cease. All told, Hans responded more or less readily to forty persons, but it was only when he worked with Mr. von Osten or with Mr. Schillings, that his responses were at all dependable. For this reason I undertook to befriend the horse, and by happy chance it came to pass in a short time he responded as readily to my questions as to those of the two gentlemen. In a few of these experiments the Count zu Castell, Count R. von Matuschka and Mr. Schillings undertook the rôle of questioner. Where these are not mentioned in the results here published, I myself did the questioning.

With regard to the number of experiments and their performance, the following precautions were observed. A sufficiently large number of tests was made in each series in order to obviate the possibility of the contention that the horse's errors were due to chance. The conditions of experimentation were such that the further contention that he happened to be tired or otherwise indisposed, whenever the reactions seemed to be inadequate, could not be offered. The possibility of confusing the horse by means of unwonted conditions also had to be avoided. For this reason it was necessary to alternate the trial in which procedure was with the knowledge of the answer on the part of the questioner, with the trial in which the procedure was without such knowledge. Such precautions had hitherto been neglected, and therefore those negative results which had been occasionally obtained in single trials, could not claim objective validity, even though the persons making the tests were subjectively convinced.

The course of the experiments was determined by the nature of the problem itself. By means of a very simple test it was possible to discover whether or not Hans was able to think independently. He was confronted with problems in which the procedure was without knowledge of the answer on the part of the questioner. If under these conditions he could respond with the correct answer—which could be the result of a rational process only—then the conclusion that he could think independently, was warranted. The examination would be closed and Mr. von Osten would be justified in all he claimed for the horse. If, however, Hans should fail in this test, then the conclusion that he could think was by no means warranted, but rather the inference that he was dependent upon certain stimuli received from the questioner or the environment. Further investigation would be for the purpose of discovering the nature of these stimuli.

To ascertain by means of which sense organ or organs the horse might receive these necessary stimuli, the method of elimination was employed. We began by excluding visual stimuli by means of a pair of very large blinders. Should this investigation be without results, then we would proceed to test the sense of hearing. The elimination of auditory stimulations would be more difficult, because ear-caps or the closing of the passage by means of cotton would not give sufficient assurance that the sound-waves were being interrupted, even if the horse were docile enough to suffer these appliances. Thereupon would follow the testing of the sense of smell and of the skin-senses. And finally there might be involved another still unknown sense, such as seems to exist in the lower animal-forms. The reader therefore can readily see that the investigation might possibly have become very complex, and that the investigator had to be prepared for all of these possibilities.

The results of the experiments and the essential circumstances under which they were conducted, were in every case recorded immediately.

It goes without saying that in the final formulation of the results, all values—including those which were not consonant with the majority—were to be used.

B. Experimental Results

During the course of these experiments Hans wore his accustomed trappings, i. e., a girdle, light headgear and snaffle, and he either stood alone, untied, or was held loosely by the bridle either by the questioner or (though only in a few instances) by his attendant. The questioner always stood to the right of the horse, as Mr. von Osten had been accustomed to do. As reward for correct responses Hans received from the questioner[G]—and from him only—a bit of bread or carrot, and at times also a square of sugar. Never was a whip applied. From time to time the horse was led about the courtyard or was allowed to run loose in order to secure the needful respite. Besides myself there was usually present Prof. Stumpf and Dr. von Hornbostel, who kept the records, and frequently also Mr. von Osten. Several times I worked alone with the horse. The results obtained in the horse's stall were in no respect different from those got in the course of the experiments carried on in the courtyard. Whenever a doubt arose as to the number of taps made by the horse (though this did not frequently occur), then the series in question was immediately repeated.

In this report of the results of our experiments, the reader must bear in mind that it was impossible to adhere to that order and distribution of tests which we are wont to require in the case of psychophysical experiments conducted under regular laboratory conditions. All sorts of difficulties had to be overcome: unfavorable weather, the crowds of curious ones, certain peculiarities of the horse—such as shying whenever the wind rippled the canvas of the tent—and last but not least, the idiosyncrasies of Mr. von Osten who repeatedly attempted to interrupt the progress of the experiments.

Since it was evident that different kinds of processes were involved in solving the problems and since the solutions would be indicated by tapping, or by movements of the head, or by walking over to the object to be designated, the results of these three sets of experiments have been grouped under three corresponding heads.

I. Problems solved by tapping

The following tests were made in which the method was such that when the problem was presented to the horse, the correct solution was known to none of those present, least of all to the questioner. This method we shall designate in the following report as "procedure without knowledge" whereas we shall call the method in which the answer was known to the questioner, "procedure with knowledge".

In order to discover if the horse could read numbers, a series of cards on which numerals were blazoned, were exposed to the horse's view in such a way that none of those present was able to see them, and the horse was asked to tap the numbers as they were shown. This experiment was repeated at different times and in all there were 49 tests in which procedure was without knowledge, and 42 in which procedure was with knowledge. In the case of the former there were 8% correct responses, whereas in the case of the latter 98% of the answers were right. As an example of the course which the series tended to take, we insert the following, in which Mr. von Osten himself acted as questioner.

Whenever the questioner knew the solution, nearly all of the horse's answers were correct; but when the answers were unknown to the questioner, the horse's responses were, with only a few exceptions, quite unsuccessful. Since the few exceptional cases must be regarded as fortuitous, the conclusion is warranted that the horse was unable to read numerals without assistance.

In order to discover whether the horse could read words such as "Hans" or "Stall" or the names of colors, they were written upon placards and hung up in a row before the horse in such a way that the questioner could see the individual word but could not immediately recognize the particular place that each one occupied in the series. The horse was then asked: "Upon which placard is the word

'Hans'?", "On which is the word 'Stall'?", etc. In order to make sure, he was required to repeat each answer.

Then the experimenter would determine for himself the place of the word in the series and would ask the question again. Fourteen such tests, in which the procedure was with knowledge on the part of the questioner, were interspersed with twelve in which the procedure was without such knowledge. With the latter there were no correct responses, whereas in the cases of procedure with knowledge 100% of the answers were correct. Evidently the horse could not read words.

Three words were thereupon whispered in his ear, which he was asked to spell in accordance with the method described on [page 21]. Since he had to indicate first the row, and then the place in the row occupied by the letter, it took two answers to indicate the position of each letter. I acted as questioner. The ordering of the table of letters was unknown to me, except the position of the letter "a", which naturally came first, and the place of the letter "s", concerning whose position I had purposely inquired. The words chosen for this experiment were "Arm", "Rom" (Rome) and "Hans". The horse responded incorrectly in the case of every letter which was unknown to the questioner. "A" and "s" alone were given correctly. Thus in spelling the word "Rom" the horse responded with the series 3, 4; 3, 4; 5, 4; 5, 4; i. e. "jjst", instead of the correct series: 4, 6; 4, 2; 3, 7. I later selected three other words, the spelling of which involved the tapping of thirty-two numbers on the part of Hans, and whose position I had carefully ascertained beforehand. When these were given to the horse to spell, he responded promptly without a single error. Evidently Hans was unable to spell without assistance of some sort from the questioner.

The horse's reputed aptitude in computation was tested in the following way. Mr. von Osten whispered a number in the horse's ear so that none of the persons present could hear. Thereupon I did likewise. Hans was asked to add the two. Since each of the experimenters knew only his own number, the sum, if known to anyone, could be known to Hans alone. Every such test was immediately repeated with the result known to the experimenters. In 31 tests in which the method was procedure without knowledge, 3 of the horse's answers were correct, whereas in the 31 tests in which the method was procedure with knowledge, 29 of his responses were correct. Since the three correct answers in the cases in which procedure was without knowledge evidently were accidental, the results of this series of experiments show that Hans was unable to solve arithmetical problems.

For the purpose of discovering whether the horse could at least count, the Russian kindergarten device, which Mr. von Osten had used in training, was utilized. The machine was placed before the horse, but the experimenter turned his back upon it. Before each test, a number of balls were pushed to one side and Hans's problem was to indicate the number thus separated. Each test was repeated with procedure with knowledge. Of eight such experiments Hans responded successfully every time procedure was with knowledge but failed every time procedure was without knowledge. Thus 7 balls were at one time designated as 9 and later as 14, while 6 were at first designated as 12, and later as 10. Since all these errors could not be accounted for on the ground of miscounts on the part of the horse, it was evident that Hans is quite unable to count.

The memory-test was conducted in the following manner. In the absence of the questioner a number or the name of some day of the week was spoken to the horse. The experimenter would then return and question him. Of 10 responses 2 were correct, 8 incorrect. Among the correct answers were the number 3, a number which, as we shall see, Hans was prone to give under all sorts of conditions, and which therefore meant very little when given as a correct response. The number 2, on the other hand, was consecutively indicated by 7, 9, 5, and 3, 8 was given as 5, 6, 4, and 6, consecutively; and finally Wednesday was indicated as the fourteenth day of the week. After this we undertook the test the horse's far-famed knowledge of the calendar. Dates, such as Feb. 29, Nov. 12, etc., were given to Hans and he was asked to indicate on which day of the week they fell. Sunday was to be indicated by 1, Monday by 2, etc. Of 14 such tests, 10 were unsuccessful, 4 successful. But in the case of these 4 something very interesting occurred. It happened that during this series the keeper of the horse was present, and he happened to know the days on which these dates fell,—as he himself testified. The dates in question were also little more than a week or so from the day of the experiment, so they could easily be determined. But as soon as we took more remote dates both man and beast were hopelessly lost. It was certain that Hans had no knowledge of the calendar. It is needless to say anything of his supposed knowledge of cards and coins. Hans plainly was incapable of the astonishing feats of memory which had been claimed for him.

Finally we investigated Hans' musical ability. In a room adjoining the horse's stall there was a small harmonica, which spanned the once accented octave. On this one or more tones were played. The horse was required to indicate the tone played, the number of tones played and their relation to one another. For testing his general hearing 20 tests were given in which the method was procedure without knowledge. Of the responses only one was correct, and that one was the tone e, for which the proper response was three taps, but we must bear in mind what has already been said of the number 3. The tone b was indicated by 11 taps, although Hans had only learned a scale of one octave and therefore could respond to only seven tones. In the tests in which the method was procedure with knowledge, he again, without exception, was successful. Similar results were obtained in the analysis of compound clangs. In the cases of procedure without knowledge (although the experimenter here knew the correct responses, he purposely refrained from thinking of them) not a single response was correct; while in the cases of procedure with knowledge, all but one were correct. The following were typical responses: Three tones were played and the question was asked, "How many tones were played?" Hans responded first with 4 taps and then with 1. The tones c, e, g, a, (1, 3, 5, 6) were struck and the question asked, "Which tone must be eliminated to make the complex a chord?" In the tests in which the method had been procedure with knowledge, this question had always been answered correctly, but when procedure was without knowledge the responses were first 13, a tone which does not exist for Hans, then 2, a tone which was not given in the clang to be analyzed, and finally 3, which was not the discordant tone. Hans's far-famed musical ability was an illusion.

Taking the results of all the tests into consideration, we find that in the case of procedure with knowledge, 90 to 100% of the responses of the various series were correct, whereas, in those series of procedure without knowledge 10%, at most, of the responses were correct. Under the conditions prevailing during these latter tests, even these 10% must be regarded as due to chance. To be sure Mr. Grabow, a member of the school board and an enthusiastic follower of Mr. von Osten (Zeitschrift für Pädagogische Psychologie, Pathologie und Hygiene, Berlin, 1904, Jahrg. 6, Heft. 6, S. 470), mentions a large number of successful tests, which were supposedly made in accordance with the method of procedure without knowledge. A thorough analysis of his experiments was not possible, because the conditions under which they were conducted were not adequately specified. But I have no doubt that the successful responses of the horse were due solely to the absence of precautionary measures. I, too, could cite a number of seemingly correct responses which demonstrably were due to the absence of adequate precautionary measures. I therefore repeat: Hans can neither read, count nor make calculations. He knows nothing of coins or cards, calendars or clocks, nor can he respond, by tapping or otherwise, to a number spoken to him but a moment before. Finally, he has not a trace of musical ability.

After all this experimentation it was evident that the horse was unable to work alone, but was dependent upon certain stimuli from its environment. The question therefore arose: does the horse get these stimuli while the question is being put, or during his responses, i. e., during the process of tapping.

If Mr. von Osten's opinion was correct, then the process of questioning played an important part in the success of the experiment. Of course, as he said, it was not necessary to ask the question aloud; it was sufficient—curiously enough—that it be inwardly spoken, thanks to the horse's extraordinary auditory sensitivity. If, however, conditions were made such that the auditory sense was eliminated, then the animal would be unable to respond. Such a theory is not quite as absurd as it might seem at first blush. For Hansen and Lehmann have shown that an acute auditory organ is able to respond to such delicate stimulation as is involved in the softest whisper, or even in the so-called nasal whisper in which the lips are tightly closed.[3] They have attempted thus to explain any modes of supposed "thought-transference", (cf. [page 7]). Since experts on horses agree that the horse has acute auditory sensitivity, Mr. von Osten seized upon this fact and tried to establish his theory in the following manner. No response was successfully made on the part of the horse, he said, when the sound waves caused by his (Mr. von Osten's) inner speech were deflected from the ear of the horse. This was the case when he closed nose and mouth while inwardly putting the question, or deflected the waves from the horse's ear by means of a placard held before his mouth while speaking, or finally by applying lined ear-muffs to the horse's ears. If, on the other hand, he closed only his nose and not his mouth while thus inwardly putting the question, or if he held the placard so that there was a possibility of deflecting the sounds to the horse's ear, or if the ear-muffs were of too sheer a material, then Hans could hear and answer the questions which for human ears were inaudible. He demonstrated all this by means of experiments and of 20 tests of the first kind, in which auditory sensations were supposedly eliminated, 95% of the responses were incorrect (Hans would always tap too great a number); whereas of 28 tests of the second kind, not a single answer was wrong, just as had been predicted. Now I have repeated both kinds of tests, but have always found some correct responses in those cases in which the horse, supposedly, was unable to hear, a thing which greatly astonished Mr. von Osten. In fact, the responses of the horse were quite as correct when I did not even whisper the question inwardly. It was quite clear that putting the question in any form whatever was wholly unnecessary. Mr. von Osten's demonstrations to the contrary, which were based upon erroneous physical principles, are to be explained as cases of vivid autosuggestions, (but of this, more in [Chapter V]). After all this experimentation, it was manifest that the cue was not given to the horse while the question was being put; it occurred, therefore, at some time during the process of tapping. But by means of which sense organ was it received by the horse?

We began by examining the sense of vision, and in the following manner. Blinders were applied, and it is worthy of mention that Hans made no attempt to resist. The questioner stood to the right of the horse, so that the animal knew him to be present and could hear, but not see him. Hans was requested to tap a certain number. Then the experimenter would step forward into the horse's field of vision and would put the same problem again. Since, in the tests of the first kind, Hans would always make the most strenuous efforts to get a view of the questioner, and since he would rave and tear at the lines whenever the attempt was made to tie him,—a thing which he had never done hitherto,—it was impossible to determine in some cases whether or not he had seen the questioner during the process of tapping. I am using, therefore, in the following exposition, besides the two categories of "not seen" and "seen", a third which I have called "undecided". A total of 102 tests were made in which large blinders were used. In 35 of these, the experimenter certainly was "not seen" in 56 cases he was "seen" and the remaining 11 are "undecided". Under the first of these categories 6% of Hans's answers were correct (i. e. only two), under the second head 89% were correct and under the third 18% were right. In other words, the horse was at a loss the moment he was prevented from seeing the questioner; whereas his responses were nearly always correct when the experimenter was in sight, certain proof that the horse's failures are to be attributed to the elimination of visual stimuli and not to the general inconvenience occasioned by the blinders. It is evident therefore, that the horse required certain visual stimuli or signs in order to make a correct response.[H]

Such unequivocal results, however, were only obtained after we had provided blinders of sufficient size (15 × 15 centimeters). Mr. von Osten believing that the horse would not suffer these to be applied, had at first proposed other measures. He held a slate before his face. Some of the horse's responses were right, others wrong. The tests were repeated and were successful as long as I, myself, held the slate before my face, but not a single one of the responses was correct when another would attempt to hold the slate before me. Mr. von Osten then brought forth a kind of bolster which he fastened on the right side of the horse's face,—the side which was turned toward the questioner. But this also gave uncertain results. Finally he agreed to apply blinders. But these were much too small and projected at a great angle from the head (Mr. von Osten had cut the straps, for he thought they worried the animal). The result was that only the posterior part of the horse's normal field of vision was obstructed. Therefore, one could never be quite sure whether Hans, who—it will be borne in mind—made every attempt to see the questioner, had not perhaps after all been able to peer over the edge of the blinder. The number of "undecided" tests, therefore, became very great. Of 108 tests, only 25 could be placed in the category of "not seen", 44 in the "seen", and 39, i. e., a third of the total, in the "undecided." The percentage of correct answers for these three categories were, respectively: 24%, 82% and 72%. Here we have once more approximately the same ratio between the categories of "seen" and "not seen" as in the case of the tests with the smaller blinders. If we were to count the cases which we had put under the head of "undecided," in the same category as those in which vision had been excluded—as Mr. von Osten had done—then one would have been led to the conclusion that the horse did not need visual signs. Several observers had thus been led astray: e. g., General Zobel writes in the "National-Zeitung" (Aug. 28, 1904), that upon request Mr. von Osten had covered Hans's right eye "by means of some sort of blinder, so that he was unable to see his instructor", and that Hans did not fail to respond correctly. We evidently have here to do with the unreliable bolster mentioned above. Furthermore, Mr. Schillings made a number of tests with the small blinders, in which 50% of the answers were correct, and probably in the same manner were obtained the results published in one of the daily papers (the "Berliner Tageblatt", Dec. 12, 1904), several days after the publication of the December report, and reading as follows: "Tests have been made upon Hans with blinders over his eyes and it is to be noted that, in spite of these, he still responds correctly." Mention is also made of the experiments noted in [Supplement III (page 257)], in which Mr. von Osten hid behind the questioner and merely encouraged the animal by occasional exhortations, but it is not possible to say with any degree of certainty in how far he was really hidden from the horse's view.

I would add that the horse—in so far as it was at all possible to decide—never looked at the persons or the objects which he was to count, or at the words which he was to read, yet he nevertheless gave the proper responses. But he would always make the most strenuous efforts to see the questioner. (See [page 43]). I would furthermore add that several experiments, in which Mr. von Osten and the horse were separated from each other by means of the canvas tent, failed completely, and that, on the other hand, all tests were successful in which the questioner was present in the feed-room and the door between this and the horse's stall was opened wide enough for him to be seen by the horse. I would also mention that toward evening the responses became less and less accurate. The conclusion that visual stimuli were here operative cannot be gainsaid.

It was possible, to be sure, that other senses might also be involved, but it was certain that auditory sensations did not enter it. This is shown by the fact that one might remain just as silent while the horse was tapping his answer as during the putting of the question and yet obtain a correct response. Hans, furthermore, could scarcely be distracted by auditory stimulations. If either the experimenter or anyone else present sought, at a given moment, to interrupt him by such calls as "Halt", "Wrong", etc., while he was going through the process of tapping, they very seldom succeeded in their attempt. Even though such interruption did succeed in seven out of the twenty-one cases in which it was tried, the assumption is well grounded that the success was due entirely or almost entirely to minimal movements involuntarily executed by those attempting the interruption. It is to such minimal movements that the horse, as we shall see later, promptly reacted. When the experimenter (Pfungst), himself, made the interjections, which certainly should have been more effective, we found that the horse was actually disturbed in only two of the fourteen cases; and finally in ten consecutive cases of attempted interruption not a single one was successful. There was almost a complete absence of any ear movements on the part of the horse, a fact in which I have been borne out by Mr. Henry Suermondt, the distinguished horseback rider. Indeed, I cannot recall that Hans ever turned his ears toward me, a fact which is strikingly curious in the case of a horse so attentive and so spirited in temper.

Finally, I might also mention that the breathing of the experimenter in no wise influenced the outcome of the experiment. Whether he held his breath or breathed on the leg or body of the horse, made no difference.

Investigations of the other senses became needless, for I had, in the meantime, succeeded in discovering the essential and effective signs in the course of my observations of Mr. von Osten. These signs are minimal movements of the head on the part of the experimenter. As soon as the experimenter had given a problem to the horse, he, involuntarily, bent his head and trunk slightly forward and the horse would then put the right foot forward and begin to tap, without, however, returning it each time to its original position. As soon as the desired number of taps was given, the questioner would make a slight upward jerk of the head. Thereupon the horse would immediately swing his foot in a wide circle, bringing it back to its original position. (This movement, which in the following exposition we shall designate as "the back step", was never included in the count.) Now after Hans had ceased tapping, the questioner would raise his head and trunk to their normal position. This second, far coarser movement was not the signal for the back-step, but always followed it. But whenever this second movement was omitted, Hans, who had already brought back his foot to the original position and had thereby put it out of commission, as it were, would give one more tap with his left foot.

If it was true that these movements of the questioner guided the horse in his tapping, then the following must be shown: First, that the same movements were observed in Mr. von Osten in every case of successful response; secondly, that they recurred in the same order or with only slight individual changes in the case of all who were able to obtain successful responses from the horse, and that they were absent or occurred at the wrong time in all cases of unsuccessful response. Furthermore, it was observed that it was possible to bring about unsuccessful reactions on the part of the horse as soon as the movements were voluntarily suppressed, and conversely, that by voluntarily giving the necessary signs the horse might be made to respond at pleasure; so that anyone who possessed the knowledge of the proper signs could thereby gain control over the process of response on the part of the horse. These requirements have all been fulfilled, as we shall see in the following pages.

With regard to the regular recurrence of the movements noticed in the case of Mr. von Osten, I was, after some practice, able to note carefully their peculiar characteristics. This was rather difficult, not only on account of their extreme minuteness, but also because that very vivacious gentleman made sundry accompanying movements and was constantly moving back and forth. To abstract from these the essential and really effective movements was truly difficult. It was much easier to observe these movements in the case of Mr. Schillings, probably on account of the fewer accompanying movements and perhaps on account of their greater distinctness. Usually he would raise the entire trunk a trifle, so that the movements could be noticed from behind. Besides these, I had an opportunity to observe the Count zu Castell, Mr. Hahn and the Count Matuschka. All three made the same movements, though somewhat more minutely than Mr. Schillings, yet none was as slight as those of Mr. von Osten.[I] I further noticed that Count Matuschka and Mr. Schillings often showed a tendency to accompany every tap of the horse with a slight nod of the head, the last being accompanied by a more pronounced nod and then followed by the upward jerk of the head, in other words, they beat time with the horse. In the case of the last three mentioned, for whom the horse responded far less effectively than for Mr. von Osten or Mr. Schillings, belated or precipitate jerks would frequently occur. This was found to be true in the case of all other persons who had failed to elicit adequate responses from the horse. Often, in both cases, a complete absence of any kind of minimal movement had been noted. The accuracy of these observations in the case of Mr. von Osten is attested by Mr. Stumpf and Mr. von Hornbostel, and by these same gentlemen and Prof. F. Schumann in the case of Mr. Schillings and myself. They also found these movements to be most minute in the case of Mr. von Osten. In my case also they pronounced them "minimal, and often quite imperceptible". All other persons who have seen me work with the horse, but who were not familiar with the nature of these movements, never perceived them, no matter how closely they observed me.

Since the doubt was expressed that these movements did not precede but followed closely upon the back-step of the horse (i. e., that an error with regard to the time-element was involved), it became important that time measurements be taken. This was done in the following manner: The questioner asked the horse to tap numbers from 5 to 20, seldom higher. He purposely refrained from pronouncing the number, but recorded it after each test had been completed. This was a matter of indifference to the horse (see [page 42]), and had the advantage that the measurement was not influenced by knowledge on the part of the time-keeper. Two observers were required, one watching the horse, the other the questioner. Both observers had fifth-second stop-watches. The larger face of this watch shows the fifth-second and a hand on the smaller face indicates the minute. By pressing upon the stem the watch may be set in motion at any moment desired, and by pressing it once more it may be instantly stopped, and the time

elapsing between the setting in motion and the stopping may be read on the face. By pressing upon the stem a third time the hands are brought back to zero, and the watch is ready for another test. At a moment agreed upon beforehand—usually the third tap of the horse—both observers started their watches. Practice tests had shown that this could be done with all the accuracy necessary in this case. As soon as the observer of the questioner noticed the latter's head movement he stopped his watch, and as soon as the observer of the horse noticed the latter's back-step he stopped his watch. Since the movement of the horse's foot does not occur as a jerk, but is of greater extent than a jerk would be, it was agreed that the observer was to stop the watch as soon as he recognized the back-step as such, not when the foot was being raised from the ground, because it was not then evident whether the horse would bring it back to the original position or whether he was preparing to give another tap, nor when he had brought his foot completely back, but at the moment in which it was evident that the horse intended to make the back-step. Experimentation had shown that an agreement as to this moment was possible. A tap with the left foot, which might possibly follow upon the back-step, could be left out of account. The difference in time between the two watches would show the time between the head-jerk of the questioner and the back-step of the horse,[J] and if the back-step was indeed a reaction upon the head-jerk, then the watches would have to show a later time for the back-step than for the head-jerk.

Measurements of this kind were taken for Mr. von Osten, Mr. Schillings and myself. In the case of the first two it was taken without any knowledge on their part. They did not even know that they were being observed, having been told that the measurements were for the sake of determining the horse's rate. In my case, to be sure, the time could not be taken without my knowledge. I succeeded, however, in eliminating the effect of this knowledge on my part. (Cf. pages [88] and [145].) Since the results obtained in the case of Mr. Schillings quite agree with those obtained in my case, it is evident they may be considered as being of equal value.

With regard to the number of tests the following table may be referred to. The first vertical column gives the name of the questioner, i. e. the person operating with the horse. The four other columns give the number of tests made upon each of these. The name of the person who made the observation in each series is indicated at the head of the column. It is unnecessary to give the name of the observer of the horse, for the only difficulty lay in the observation of the questioner. The numerals I and II indicate two series taken at different times.

We have omitted from this table several tests in which the observer of the questioner noticed no head jerks whatever, and therefore could not arrest his stop-watch, although the horse responded correctly. Four tests of this kind were made by Mr. von Hornbostel, two by Mr. Pfungst, two by Mr. Schumann and five by Mr. Stumpf. In the case of Mr. Pfungst the horse gave the unusually high number of fifty taps. The attention of the observer had been taxed too long and had failed him (two seconds is the most favorable time). The head-jerk of Mr. von Osten evidently occurred during a lapse in Mr. Pfungst's attention and therefore remained unnoticed.

The results of the experiments are given in the second table. The general arrangement corresponds to that of the first table. Even though the absolute number of tests was small, yet for the sake of giving a better general view, all values are given in percentages. The tests in which the movement of the questioner had preceded that of the horse—as had been anticipated—are recorded under "R" (right); under "W" (wrong), we have recorded those cases in which the testimony of the stop-watches—contrary to our expectation—indicated that the reverse order prevailed. Finally, those cases which would complete the 100%, i. e. those in which the watches indicate simultaneity of the movements in question, are not recorded.

From this table we may note the following: The time-measurements for Mr. Schillings and Mr. Pfungst are quite in agreement and go to show that the order in time of the head movement of the questioner and the back-step of the horse was exactly what had been expected. The few contradictory cases which occur in Series I of the observations upon Mr. Schillings are to be accounted for by the fact that he was here for the first time the subject of observation, whereas the recorded time-measurements in the case of Mr. Pfungst had been preceded by a number of practice tests. The results of the measurements taken in the case of Mr. von Osten were far less satisfactory. Even if one were to allow a series containing barely more than 50% of "right" cases as sufficient proof of the correctness of our expectation regarding the order of the movements of the questioner and the horse, only three of the six series obtained with Mr. von Osten as subject, would satisfy this expectation. However, since four of the six series show a greater number of cases of simultaneity (their percentage may be easily deduced by referring to the per cent of "right" and "wrong" cases), the proposed method would give a distorted view, and therefore it appears that the more correct method would be to consider simply the numerical ratio of the "right" and "wrong" cases. Since, furthermore, Series II shows, in every case, a decided change which is similar for all observers (note especially Pfungst), there can be no doubt but that practice is here involved, and that Series II is to be regarded as the true standard. Throughout this series we find a preponderance of "right" cases. Therefore, the table unmistakably confirms the expected order in time. That there were more "wrong" cases with Mr. von Osten as subject than with the other questioners is to be explained by the fact that the decisive movements were far less easily observed in this case, than in that of the other questioners. (See [page 49].) We expect that Series III would show the same results, or approximately the same results in the case of Mr. von Osten that it did for Mr. Pfungst and Mr. Schillings, but unfortunately he declined to act as subject. In the meantime, however, new and decisive proof presented itself which destroyed all possible doubt.

Before adverting to it, let us consider in a few words the reaction-time of the horse,—the time elapsing between the final sign of the questioner and the reaction of the horse (i. e., the back-step). Unfortunately this time cannot be directly determined. All that can be ascertained from our time-measurements, is the time intervening between the moment of the head-jerk and the moment in which the reaction of the horse is noted. (See [page 51]). This time averaged, for the 127 measurements, .45 seconds. If we stated the unavoidable error, (obtained on the basis of extended supplementary measurements which it is not necessary to consider here) as .15 seconds, and apply it to the value found above, we obtain .3 seconds as the probable reaction-time of the horse.[K]

That the tapping—as well as all other movements of the horse—was nothing other than a reaction upon certain visual stimuli, was proved beyond a doubt by the fact that the voluntary execution of the head-jerk and of other movements—which we will describe in more detail later on,—brought about all the proper responses on the part of the horse. Thus, artificial synthesis became the test of the correctness of analytical observation.

To elucidate; if the questioner retained the erect position he elicited no response from the horse, say what he would. If, however, he stooped over slightly, Hans would immediately begin to tap, whether or not he had been asked a question. It seems almost ridiculous that this should never have been noticed before, but it is easily understood, for as soon as the questioner gave the problem he bent forward—be it ever so slightly—in order to observe the horse's foot the more closely, for the foot was the horse's organ of speech. Hans would invariably begin to tap when I stooped to jot down some note I wished to make. Even to lower the head a little was sufficient to elicit a response, even though the body itself might remain completely erect. Of thirty tests made in this position, twenty-nine were successful. Hans would continue to tap until the questioner again resumed a completely erect posture. If, for instance, I stooped forward after having told the horse to tap 13, and if I purposely remained in this position until I had counted 20, he would, without any hesitation, tap 20. If I asked him to add 3 and 4, but did not move until 14 was reached, he would tap 14. Twenty-six such tests gave similar results.

The reaction of the horse upon such a signal for stopping showed slight modifications according to the time which elapsed between the last tap and the signal for stopping. These modifications, which had hitherto been paraded as expressions of the horse's psychical power may be illustrated by the following schematic figures (Figures [1]-[4]). In all of them the dotted line c-d represents the ground level; d shows where the horse's right forefoot was located before he began tapping; a and c, respectively, indicate the place to which the foot is lowered during the process of tapping. The unbroken line gives the direction of the back-step.

If Hans, having raised his foot from a to b—preparatory to tapping,—receives the signal at or just before the moment he lowers the foot, he immediately swings it in a wide circle from c back to its original position at d, ([Fig. 1]). As a matter of fact a and c coincide, but are juxtaposed in the diagram for the sake of schematic

utility. This was the usual form of the back-step.

Fig. 1.

If the signal for stopping is given a little after the last tap ([Fig. 2]), i. e., at the time that the foot is already being raised for another tap, then the back-step occurs as a-b-d. The horse thus gives, at the moment it receives the signal for stopping, a changed impulse to the moving foot. The curve, therefore, has a kink at b, and the back-step occurs with seeming hesitancy,—Hans appears not quite certain of his result.

Fig. 2.

If the signal be given somewhat later still ([Fig. 3]), i. e., when the foot is being lowered to complete a tap, Hans is still able to put on the brakes—as it were—and draw back his foot before it reaches the ground. The whole process gives the impression that the horse was just about to make a "mistake" of one unit, but at the last moment had bethought himself of the correct answer.

Fig. 3.

Finally, if the signal be deferred still longer, it becomes impossible to prevent the extra tap. The back-step again has the same form as in [figure 1]; Hans has made a "mistake" in his answer by one unit too many.

Conversely, if the head-jerk of the questioner occurs too soon; i. e., at the moment the horse has raised his foot for the final tap to the height b, ([Fig. 4]), then the tap is not completed,—but the foot, without touching the ground, makes the curve b c₂ d, back to its original position. Hans has again made a "mistake" in his answer,—this time by one unit too few.

Fig. 4.

All these variations go to show one thing: Hans never knows in advance which tap is to be the final one. These variations in his reactions occurred often without having been intended by the questioner. But to bring them about at will required skill, on account of the shortness of the time involved in the reaction.

Whenever the signal for stopping—which we have just discussed—was followed by the complete erection of the head and trunk, Hans would definitely cease tapping. If, however, the questioner failed to assume a completely erect position, or if he stooped forward ever so slightly, the horse would follow the back-step of the right foot with an extra tap of the left foot. Besides occurring in tests in which Mr. von Osten assumed the rôle of questioner, this fact was also noted when the Count zu Castell and Mr. Schillings acted as subjects. Since the extra tap just mentioned was not given like the others with the right foot forward, but with the left foot upon the spot, it was possible for the horse to execute it with a greater show of energy. This simulated a high degree of mental certainty on the part of the horse, as if he wished to indicate that this was the correct solution of the problem and it would have to stand. In spite of all this, many errors would creep in. It was possible to prolong this extra tap and thus make it appear more dilatory. We need hardly add that henceforth it was within the power of the experimenter to have the tapping executed entirely with the right foot or with the final extra tap of the left foot. Hitherto the view had been current that this lay solely within the pleasure of the horse.

If the questioner still inclined forward, still remained in the bent posture after Hans had given the final tap with his left foot, the horse would immediately begin to tap once more with his right foot, which had, in the meantime, become ready for further action. If the head jerk was then made, Hans would bring his right foot back, give the extra tap with his left foot, then resume tapping with the right and thus continue until the questioner once more resumed the erect posture. Thus the horse on one occasion when I wished him to tap 100, gave—contrary to my desire—the following response; 39 with the right foot, 1 with the left, 24 with the right, 1 with the left, 35 with the right, and 1 with the left. Later it became possible for me to cause him to tap 1 right, 1 left, 1 right, 1 left, etc. I could even get him to tap exclusively with the left foot by standing at his left rather than at his right as had been customary with his questioners. These taps with the left foot were executed in a far less elegant fashion than those with the right foot, and with a great waste of energy. Hans had become a right-handed individual—as it were—as a result of long habit.

With regard to the distance at which the experimenter directed the horse, the following may be said: The usual distance was one-quarter to one-half meter. This holds for all tests hitherto described. Seventy tests which were made for the purpose of discovering the influence of change in distance showed that the reaction of the horse upon the customary signal of the head-jerk was accurate up to a distance of three and one-half meters. At a distance of three and one-half to four meters there suddenly occurred a fall of 60-70% in the number of correct responses. At a distance of four to four and one-half meters only one-third of the responses were correct, and at a distance beyond four and one-half meters there were no correct responses. The greater number of these tests were made in our presence by Mr. von Osten, who was under the impression that we were testing the accuracy of the horse's hearing, whereas we were really testing the accuracy of his perception of movements.

With regard to the different positions which the experimenter might assume with reference to the horse, the following may be noted: The normal position was to the right of the horse. If the experimenter stood immediately in front of Hans, the latter's reaction would be just as accurate, though he would always turn his head and make desperate efforts to see the questioner, even though he was held in short by the reins. When a position immediately behind the horse was taken—a somewhat dangerous proceeding, since Hans would at once begin to kick—no response could be obtained until he succeeded in turning far enough around to get the questioner within view. If he was restrained from turning completely around, he would at least turn his head,—and always to the right. One might even turn his back upon Hans during the tests, for the signal for stopping was not obtained from the face of the questioner, but from a movement of the head. The following incident will show to what extent the horse had become accustomed to seeing the questioner in a certain definite position. For a long time I had been in the habit—without exception—of standing close to the horse's shoulder. Mr. von Osten, on the other hand, would stand farther back. When, on a certain day, I assumed the latter position, the horse would not suffer it, but would move backward until he had his accustomed view of me.

Finally we sought to discover by what movements the horse could be made to cease tapping. We discovered that upward movements served as signals for stopping. The raising of the head was the most effective, though the raising of the eyebrows, or the dilation of the nostrils—as in a sneer—seemed also to be efficacious. However, it was impossible for me to discover whether or not these latter movements were accompanied by some slight, involuntary upward movement of the head. The upward movement of the head was ineffective only when it did not occur as a jerk, but was executed in a circuitous form,—first upward and then back again. Such a movement was occasionally observed in the case of Mr. von Osten. The elevation of the arms or of the elbow nearest the horse, or the elevation of the entire body was also effective. Even if a placard, with which the experimenter tried to cover his face, were raised at a given moment, the horse would make the back-step. On the other hand, head movements to the right and to the left or forward and back, in fine, all horizontal movements, remained ineffective. We also found that all hand movements, including the "wonderfully effective thrust of the hand into the pocket filled with carrots", brought no response. I might also change my position and walk forward and then backward some distance behind the horse, but the back-step would only occur in response to the characteristic stimulus. After what has been said it is easy to understand how vain were Mr. Schillings' attempts to disturb the horse and how naturally he might conclude that Hans was not influenced by visual signs. Mr. Schillings simply did not know which signs were effective.

While the horse could thus be interrupted in the process of tapping by movements which were executed at the level of the questioner's head, yet movements below this level had the opposite effect. If Hans showed that he was about to cease tapping before it was desired, it was possible to cause him to continue by simply bending forward a trifle more. The greater angle at which the questioner's trunk was now inclined caused the horse to increase the rate of tapping. The rule may be stated thus: The greater the angle at which the body inclined forward, the greater the horse's rate of tapping, and vice versa. It was noticeable that whenever Mr. von Osten asked for a relatively large number—in which case he always bent farther forward than in the case of smaller numbers—Hans would immediately begin to tap very swiftly. Not being entirely satisfied with these observations, the following more exact measurements were taken. I asked the horse to tap 20. From 1 to 10 I held my body at a certain constant angle, at 10 I suddenly bent farther forward and retained this posture until 20 had been reached. If there existed a relationship between the angle of inclination and the rate of tapping, then the time for the last ten taps ought to be less than for the first ten. Of 34 such tests 31 were sucessful. The following are two specimen series.

The first series consisted of ten tests of 15 taps each. In all cases my head was bent at an angle of 30° to the axis of the trunk, but I constantly changed the angle of inclination of the trunk. It was not possible to measure this angle accurately on account of the rapidity with which the whole test had to be made. I was able, however, to differentiate between them with enough accuracy to designate the smallest angle (about 20°) as belonging to Grade I, and the greatest angle (about 100°) as belonging to Grade VII. By fixing certain points in the environment, it was possible to get approximately the same angle repeatedly. The time from the third to the thirteenth tap was, in all cases, taken by Prof. Stumpf by means of a stop-watch. The tests were taken in the following order:

From this series it will be seen that in the case of the same angle of inclination (II and VI were repeated and III was omitted) the same rate obtained in the tapping. In two other tests I constantly increased the angle of inclination during the 15 taps, and Hans gradually increased the rate of tapping accordingly.

In a second series I had the horse tap 14, five times. I myself took the time of the taps up to 7 by means of the stop-watch, while Prof. Stumpf took the time of the taps from 8 to 13. At 8 I suddenly bent forward a little more and retained this position until tap 13. The results were as follows:

Such good results, however, were possible only after a number of preliminary practice tests had been made. The experiment was especially difficult because the horse was often on the point of stopping in the midst of a test. This was probably due to some unintentional movement on my part. In such cases I could induce him to continue tapping only by bending forward still more, but this effected also, as we have seen, an increase in his rate of tapping. Such tests, of course, could not give unambiguous results.

The rate of tapping was quite independent of my rate of counting. Thus, if I counted aloud rapidly, but bent forward only very slightly, the horse's tapping was slow and lagged behind my count. If I counted slowly but bent far forward, Hans would tap rapidly and advance beyond my count. Thus we see that his rate of tapping was in accordance with the degree of inclination of my body and never in accordance with the rate of my counting, i. e., it was quite independent of every sort of auditory stimulation.

Direct observation and a comparison of the records of the time Hans required in giving to his master responses involving small, medium and large numbers, with the records of the time which he required to respond to my questions when I bent only slightly, moderately or very far forward, proved that the increased rapidity in tapping in the case of large numbers, which many regarded as an evidence of high intelligence, (see [page 20]), was, as a matter of fact, brought about in the way described. The two series (in each of which the time measured was for 10 taps) are quite in accord. The horse did not tap faster because he had been given a large number by Mr. von Osten, but because the latter had bent farther forward.

From all this it readily appears why it was possible to cause Hans to increase his rate of tapping but not to decrease it. To do the latter would involve a decrease in the angle of inclination of the body. This would necessitate the erection of the body. As we have seen, this was the signal to which Hans reacted by ceasing to tap. And as a matter of fact we never knew the horse to decrease his rate of tapping in the course of any single test, except in the case of very large numbers, and then it was probably due to fatigue. Mr. von Osten insisted that Hans often slowed down toward the end of a test, "in order to obviate mistakes", but all the tests in which he tried to demonstrate this to us, were unsuccessful. In spite of all exhortation, Hans would tap either uniformly or somewhat more rapidly as soon as his master—in all probability unconsciously—bent somewhat lower. Only once was such a test successful. Mr. von Osten—upon our request—asked the horse to give a certain large number. In this instance the decrease in the rate of tapping was due to fatigue and had nothing whatever to do with the desire on the part of the horse to avoid error.

Furthermore, Mr. Hahn, who had visited Hans twenty times and had made careful notes of his observations, corroborated my statement when he said that he himself never noted the decrease in rate mentioned. Contrary statements may perhaps be due to the fact that the tense state of expectancy on the part of the observer made the interval between the last taps appear subjectively somewhat longer.

So much for the technique of the tapping. Now a word about the numbers which Hans tapped. (I refer only to the results obtained in series which involved no volitional control). The number 1 was very difficult to get. Hans usually tapped 2 instead. Thus even in the case of Mr. von Osten he responded five times with 2, and only in the sixth test did he react correctly. As far as other questioners were concerned, 1 was seldom ever obtained, except in the case of Mr. Schillings and myself. The numbers 2, 3 and 4, on the other hand, were very easily obtained and, above all, 3 seldom failed. 3 seemed to be the horse's favorite number and was very frequently given instead of other numbers. Thus, one-sixth of all the horse's incorrect responses which were given to me were in terms of the number 3. The numbers 5 and 6 were a little more difficult to obtain and above 10 the difficulty increased rapidly. Indeed, I never saw Hans respond with a number exceeding 20 to any questioner, Mr. Schillings and Mr. von Osten excepted. I saw the nine vain attempts of Count zu Castell to get the number 15, and Count Matuschka's eight unsuccessful attempts to obtain the number 16 as a response. But even with Mr. von Osten and Mr. Schillings such failures were not infrequent. Thus, Mr. von Osten tried five consecutive times to obtain the number 24. I myself did not fare any better at first. But the following table shows what practice can do. If we compare the percentage of correct responses (involving the numbers 1 to 7—for which alone I have sufficient material, viz., 80 to 100 cases), obtained in the first half of our tests, with that of the second half, we get the following:

From this we see how hard it was at first to get the number 1 and that failure was as frequent as success, and how much easier it was on the other hand to get the numbers 2 and 3 (and which, therefore, do not show any great improvement in the second half of the tests). Beyond the 3 the percentage of correct responses decreased and the number 7 stood at the same level as the number 1. In the second half of the tests, all these differences disappeared and errors were infrequent and seldom exceeded +1 or -1. These results of practice are not to be accredited to the horse, but to the experimenter, who was at first quite unskilled. This difference in results does not appear in the case of Mr. von Osten, for his initial practice had been had many years previous. The values obtained in his case were very constant throughout our experimentation and generally showed something like 90% of correct responses. To be sure, in his case also, the number 1 was somewhat unfavorable, (79% were correct responses). But the percentages obtained in his case showed no improvement 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 to Hans in von Osten's absence and which formed the initial number of some mathematical operation, was tapped correctly. This may possibly be explained by the assumption that this initial number had been retained in the memory of some of those present, (see [page 149], on the "perseverative tendency"), and that the horse, since he had been working with some of them, responded to one of those present. Chance may have played some part also.

If the questioner knew the number of taps desired, (which was not the case with the tests hitherto discussed), then the environment had still less influence upon the horse—except that it caused occasional interruption. The horse's responses, therefore, did not tend to become more successful just because a number of persons were simultaneously concentrating upon the result desired. This was proven by the experiments which we repeatedly made for this purpose. Only one person at a time had any influence upon Hans. If two questioners tried to influence the horse at the same time,—other conditions being the same,—success would be for the one who had the greater control over the animal when working alone with him. Prof. Stumpf and I made the following experiment. Both of us stood to the right of the horse, each thinking of a number. In ten such tests Hans always tapped my number. When Stumpf concentrated upon 5 and I upon 8, the horse responded with 8, i. e., the larger number. When Stumpf had 7 in mind, and I had 4, the response would be 4, i. e., the smaller number. When Stumpf thought of number 6, and I had fixed upon none, Hans tapped 35. He was evidently awaiting my signal. When I went away Stumpf again demanded the number 6, and the horse responded properly. When I returned, Stumpf's attempts again failed. On another occasion Count Matuschka put a number of questions, while Mr. von Osten stood behind him. All of the horse's responses were correct, even the one answering the question: "How much is 7 times 7?", which was difficult on account of the great number of taps required. I was able to note from the direction of the horse's eyes that he was attending only to his master and not to the Count. On still another occasion Mr. Grabow sang two tones—the second being the fourth of the first—and asked Hans: "How many intervals lie between?" I was standing erect before the horse, and was thinking intently of the number 2, but without giving any voluntary sign of any sort. Hans tapped 2, whereupon Mr. Grabow put a number of similar questions; but I no longer thought of the answers, and all of Hans's responses went wrong.

Although Hans was not influenced by others so long as a suitable experimenter was present, yet he might be disturbed and under certain conditions might be led to make the back-step in response to certain movements in his environment. The person to whom he responded would have to be close to the experimenter and would necessarily have to execute a movement greater in extent than the experimenter's. In such instances the raising of the head, arm or trunk, was a sufficient stimulus. Thus we made the following two series of tests. Mr. Stumpf stood with trunk bent forward before the horse, and at a moment decided upon beforehand, assumed an erect position. I myself stood beside Hans and asked him to tap. When I stood at the horse's neck, then Mr. Stumpfs interruption was effective. When I stood at the horse's flank, the interruption effected only a seeming hesitation, and when I moved still farther back, the horse continued to tap despite any attempted disturbance. In the second series the questioner remained constantly at the right shoulder of the horse, while the one who attempted to distract him, changed positions. When the latter stood to the right immediately in front of or beside the questioner, the disturbance was effective in 10 out of 13 cases. But when he stood back of, and to the right of, the questioner, the attempts at disturbance were seldom successful. If he chose a place before and to the left of the horse, there was hardly any distraction (in 4 cases only, out of 13), and if he stood to the left and behind the animal, he exerted no influence whatever. Hans manifestly turned his attention, almost exclusively, to the side at which the questioner stood.

That knowledge of this modus operandi made it possible for those persons to get responses from the horse, who hitherto had been unsuccessful, is shown in the case of Mr. Stumpf when he began to control his movements voluntarily on the basis of observations which had been made.

II. Problems which Hans solved by movements of the head.

We are here concerned with the horse's head movements upward, downward, to the right and to the left, and also with nodding and shaking of the head to signify "yes" and "no". We soon discovered that these experiments, also, were successful without an oral statement of the problem,—in other words, the auditory stimulus was quite superfluous. The tests with the blinders showed that Hans was lost as soon as his questioner was out of his view, but responded adequately the moment the questioner was in sight. Hans, therefore, had established no idea of any sort in connection with the terms "up", "down", etc., but in these cases, likewise, he reacted in response to certain visual stimuli. The nature of these stimuli I discovered at first in my observations of Mr. von Osten and also of myself, when working with the horse.

Above all things it was necessary that the questioner, during these tests, should stand perfectly erect. If he stooped ever so slightly, the test was unsuccessful. If he carefully refrained from any movement whatsoever, and looking straight before him asked the horse, "Which direction is right?" or "Which way is upward?", Hans would execute all sorts of head movements without rhyme or reason. It was evident that he noted that a head movement of some kind was expected of him, but did not know the particular one that was wanted. But if the questioner now raised his head, Hans would begin to nod and would continue doing so until the questioner lowered his head. This reaction was interpreted as signifying "yes". Mr. von Osten had always asked Hans before each of the more difficult tests whether he had comprehended the meaning of the problem, and was reassured only upon seeing the horse's affirmative response. But contrary to Mr. von Osten's expectation, Hans also responded in this manner after a pair of ear-caps had been drawn over his ears. In the case of the tests described at the beginning of the chapter, in which the method was that of "procedure without knowledge", Mr. von Osten had always insisted that we await Hans's nod of comprehension before proceeding. We complied; Hans nodded and—regularly disgraced himself!

When the questioner raised his head somewhat higher than normal, Hans would throw his own upward, which was supposed to signify "upward". A lowering of the head on the part of the questioner was followed by a lowering on the part of Hans, which was his form of response for "down". For some time I was in a quandary as to the difference between the questioner's signal for this latter response and the one which was the signal for the horse to begin tapping, although I had often given both kinds unwittingly. Further experiments showed that Hans responded with a nod of the head whenever the questioner, while bending forward, chanced to stand in front of, or to the side of the horse's head, but that he would begin to tap in response to the same signal, as soon as the experimenter stood farther back. The difference in the two signals, therefore, was very slight, and I repeatedly noted that instead of tapping, as he had been requested, Hans would respond to the Count zu Castell's and Mr. Schillings' questions by a nod of the head.

If, while standing in the customary position to the right of and facing the horse, the questioner would turn his head a little to the right—a movement which, when seen from the horse's position, would appear to be to the left,—Hans would turn his head to his left. But if on the other hand the questioner would turn slightly to the left,—i. e. seen from the horse's position, to the right,—then Hans would turn his head to his right. And finally, whenever the questioner turned his head first to the right, then to the left, Hans would respond by turning first to his left, then to his right. This, according to Mr. von Osten, signified "zero" or "no". Since this movement could not be executed by the experimenter while in a stooping position, it can now readily be seen why it was that Hans, instead of shaking his head, always began to tap whenever a placard with "O" upon it, was shown to him in the course of the experiments in which the method was procedure without knowledge on the part of the questioner. The latter expected the horse to tap, and therefore bent forward. Like all of the horse's other forms of response, this, too, was always unsuccessful whenever the questioner stepped behind the animal. Although Hans had always responded to Mr. von Osten and Mr. Schillings, and at first also to me, by means of the stereotyped movement of the head to the right and then to the left to signify "zero" or "no", I later succeeded in controlling my signals so as to get the inverted order in the horse's response. In the case of Mr. Schillings and of Mr. von Osten all of the movements just described were very minute, and long after the movements, which were effective stimuli for releasing the process of tapping, were recognized, it was still exceedingly difficult to discover them in these two gentlemen. The signal for "zero" and "no" was relatively the most pronounced of the group in the case of Mr. von Osten, while with Mr. Schillings it was the least pronounced, in comparison with his very strong "jerk". Yet in both cases Hans responded

with absolute certainty.

It is now readily conceivable how it was possible to make the horse respond to all sorts of foolish questions, both by involuntary signs—i. e., expressions following upon the bare imaging of the response expected,—as well as by means of controlled signs. One could thus obtain consecutively the answers "yes" and "no" to the same question. Or one might ask: "Hans, where is your head?", and Hans would bend to the earth. "And where are your legs?" He would look at the skies. Etc.

Let us examine for a moment the directives which the horse required for the various positions. If one called him, while he was running about the courtyard, he paid no attention whatever, but if one beckoned to him, he came immediately. A raising of the hand brought him to a standstill. If one now stepped forward or pointed one's hand in that direction, he would step forward, or vice versa, he would step backward. By means of minimal movements of the head, of the arm nearest the horse, or of the whole body, Hans could be induced to assume the position one desired, without touching him or speaking a word. I noticed this quite early in the course of the investigation. Once, when intending to ask the horse to step backward to the right, I inadvertently said "Step backward to the left!", whereupon he stepped backward to the right. In spite of my verbal error, I had involuntarily given him the proper directives.

Finally we may note that Mr. von Osten had occasionally asked the horse to jump or to rear. The command in this case was: "Jump", or the question was: "What do the horses do in the circus?". Since these tests were just as effective when the command was given silently, it was an indication that these, too, depended upon visual stimuli. What was necessary to cause the horse to step backward and then jump forward was to step backward oneself, or make a slight movement of the hand in that direction. If one wished to make him rear, it might be effected by throwing the arm or head slightly upward.

III.

Problems which Hans solved by approaching the objects to be designated.

The method pursued in these tests was the following: From five to eight pieces of colored cloth ½ × ¼ meters in size were arranged in changing series upon the ground, the interval between them being equal to the width of one piece, or else they were hung upon a string a man's height above the ground. This method was also employed when placards of like size with written symbols were used. The horse stood ten paces away and opposite the middle of the series, while Mr. von Osten stood at his right. Hans was asked to go and point out the cloth of a certain color or the placard with a certain word upon it. If the cloth lay upon the ground, Hans picked it up with his mouth and carried it to the questioner. If the cloth, like the placards, hung from the cord, he approached, pointed it out with his nose and then backed up to his original position. Before approaching the objects, Hans was required to indicate, by tapping, the number of the place in the series (counting from left to right), which the cloth or placard occupied. Mr. von Osten never omitted this requirement. Then the command "Go!" was given, and Hans obeyed. (As a matter of fact, a slight directive movement of the head or hand was just as effective as the spoken command).

The following cases, chosen in a haphazard fashion, show that the horse's indication of the object's place in the series, by means of tapping, was by no means a guarantee that he would point it out correctly. Five placards hung from the cord. Mr. von Osten asked: "What is the position, counting from left to right, of the placard which has the word 'aber' inscribed upon it?". Hans answered: 3. (It was indeed the middle placard.) Then he was commanded: "Go!". Thereupon Hans went straight to the fourth placard. On another occasion Hans happened to drop a brown cloth upon a black one. His master asked him: "In which place are there two cloths?". Hans responded correctly, "In the second place". To the question "Which of the two is the black one?" he also answered rightly: "The lower one". Upon being asked to get it, he brought the white cloth.

The large number and the irregularities of the errors showed that there was no manner of intelligence involved in the pointing out process. Thus during the two months of our experimentation Hans was asked twenty-five times by Mr. von Osten to bring the green cloth. Only six times did he succeed in the first attempt, while in five instances he selected an orange-colored cloth, four times a blue, three times a white one.

The fact that the errors were equally distributed over the tests with the colored cloths and those with the placards is strong evidence that the horse's response involved no intellectual process, for if that were the case, then the responses in the tests with the placards would have been very much more difficult, for they would have involved the ability to read, whereas the tests with the colored cloths demanded only that a few names be remembered. Nevertheless, the horse was as unsuccessful in tests of one kind as he was in those of the other,—even when Mr. von Osten acted as questioner. (50% failures in 78 placard tests; 46% failures in 103 color tests.)

The fact that commands which were purposely enunciated poorly, or else not spoken at all, were executed with just as much accuracy as those given aloud, strengthened us in our supposition. On one occasion I placed a blank placard with the others. When I ordered him to approach tabula rasa, he invariably went to the right one. The following illustrates how he fulfilled quite nonsensical commands. A series of blue and green cloths lay upon the ground. Being asked where the black, the orange, and the yellow cloths lay, Hans shook his head energetically, i. e. they were not there. And yet, upon being asked to bring them in the order named, he regularly brought one of the blue ones.

All this goes to show that Hans did not know the names of the colors (to say nothing of the symbols on the placards). It was plain that here also, as in all the other cases, he was controlled by signs made by the questioner, the nature of which I soon discovered. Standing erect, Mr. von Osten always turned head and trunk in the direction of the cloth or placard desired. Hans, keeping his eye on his master, would proceed in that direction. Even after he had already started out, thanks to his large visual field one could control his direction by turning slightly more to the right or to the left. If, however, he had already arrived at the row of placards or cloths, this method ceased to be effective, for then he could no longer see the experimenter. It made no difference whether the cloths lay on the ground, or were suspended, like the placards.

The following fact justifies the conclusion that the bodily attitude of the questioner was the effective signal. The more numerous the cloths, or the nearer they were placed together, the more difficult one would expect it to be for the horse to select the one indicated by the experimenter. Such was indeed the case, for the number of errors increased with the number of cloths presented.

But no matter how many cloths there might be, or how closely they might be placed, it was always possible to indicate either end of the row, for in that case one had merely to turn to the extreme left or the extreme right, and might even turn beyond the row. Hans seldom failed in these cases, whereas he made many errors when cloths or placards within the series were wanted.

To turn from the nature and number of Hans's errors, to their distribution,—observation proved the hypothesis that the nearer two cloths lay together, the greater was the chance of their being mistaken one for the other. If we designate as "error 1" all those cases in which Hans went to cloth II instead of to cloth I, cloth III instead of cloth II, to V instead of IV, etc., and as "error 2" when he mistook III for I, IV for II, in fine, whenever he went two places too far to the right or left, and as "error 3" whenever he went three places too far to either side of the cloth desired, we find the following grouping of errors:

The most frequently recurring error, therefore, was the one in which the horse, instead of going to the cloth desired, approached the one immediately adjacent. On [page 79] I said that Hans's errors were without system, but only in so far as it was impossible to explain them on a basis of the colors which seemingly were mistaken one for the other. A part of a series in which Mr. von Osten acted as questioner may serve as an illustration. The order given is that of the experimental series as it occurred. Five colored cloths were used.

The interpretation of this series which it would be hard to explain by a reference to the colors which were mistaken, is simply this: Cloths lying near together were regularly mistaken on the part of the horse.

Experimental control of the questioner's movements decided the question. If the questioner at first indicated the proper direction and then turned about after the horse had already started forward, he was as a rule misled. When the questioner did not face the cloths at all, but turned away at right angles, or when he turned his back upon them, Hans was completely at sea. If, on the other hand, the cloths were arranged, not in a row, but in several heaps, so that one might turn to a particular heap, but could not indicate a particular cloth, then Hans would regularly go to the proper heap, but would always bring forth the wrong cloth. After much persuasion Mr. von Osten consented to make a series of these tests himself. Hans's failures were deplorable. He would take up first one cloth then another, turn again to the first, etc. We would mention, however, that this apparent searching was not done spontaneously, but in

response to Mr. von Osten's calls, such as "See there!", "The blue!", etc. Every time Mr. von Osten called, Hans would drop the cloth he was holding in his mouth, or he would turn away from the one he was about to grasp, and would then try another

one.

In addition to these visual signs, the horse received auditory signals in these tests, (as in all others in which he was required to bring objects). As soon as the questioner noticed that Hans was about to take up the wrong cloth, all that was necessary to make him correct his error was to give some sort of an exclamation, such as "Wrong!", "Look, you!", "Blue!", etc. Hans would pass on as long as the calling continued. If he was picking up, or about to pick up, a cloth when the exclamation was made, he would go on to the next; but if, at the time he was on his way to a certain cloth, he would change his direction in response to the call. If he stood before one of the pieces at the time, but had not lowered his head, he would pass on to the next. In all this he would adhere to a certain routine of procedure. If he was approaching a series from the right, then a call would cause him to turn to the left, if he was coming from the left, he would turn to the right. If he had approached the row of cloths near the center, he would turn, in response to the questioner's calls, to the left,—seldom, very seldom, to the right. Mr. von Osten did not seem to be able to control the responses of the horse, entirely. As a rule, but not always, one call sufficed to make Hans pass on to the next cloth. If too many calls were given, he would often go too far. Loud exclamations were superfluous.

These statements are not mere assertions, but are founded upon the records of the results. The tests in which calls were made show a larger percentage of correct responses than do those without calls. Of a total of 103 tests with colored cloths, which Mr. von Osten performed for us, only 37% brought forth successful responses on the part of the horse when visual signs were the only directives and when there were no directions by means of calls, whereas the total percentage of successful responses was 54%, if we add to the above those in which the vocal exclamations helped to bring about success. The corresponding percentages for the total of 78 tests with the placards were 23% and 50%. In a total of 110 color tests I myself obtained 31% correct responses under the first head, and 56% under the second head. In a total of 59 tests with placards I succeeded in getting 31% correct responses under the first head and 46% under the second head. We must note that without verbal admonition only one-third of the tests brought forth correct responses, whereas one-half succeeded when those in which calls were used, are added. Still, this is a relatively poor showing. In the most favorable series that Mr. von Osten ever obtained in our presence—and there was only one such—50% of the responses 'without admonition' were correct, and 90% when all the correct reactions, both with and without admonition, were taken into account.

Not all the places in the row required the same amount of assistance by means of calls. Those positions which needed the most help, were those which it was most difficult to indicate to the horse by the visual sign, i. e., the attitude of the questioner's body. We noted above ([page 81]) that the cloths at either end of the row were less difficult to point out than those nearer the middle. If our hypothesis holds true, we would expect that the end cloths would involve fewer auditory signals in the process of pointing out, and those within the row a greater number of such signs. By way of illustration, I will cite one series of tests in which Mr. von Osten was questioner, chosen not because it is most conformable to my hypothesis but because it is the longest (48 consecutive tests with five cloths) which I have. In the upper row I am placing the successful responses without auditory signs, in the lower those involving both auditory and visual signs.

We see that without verbal admonition the first and last places are most favorable for success, the second and fourth far less, and the middle least favorable. These differences disappear when admonitions are introduced, for all of the places then have the same number of correct responses with the exception of the middle, which now has even more than the others.

One more experiment which I made will close the discussion. The following colors were placed from right to left: orange, blue, red, yellow, black, green. I turned my back upon them, and therefore could guide the horse by verbal commands only. I asked him to bring the orange. Hans approached the yellow. I now called three times, allowing a short interval between the calls. At the first "Go!" he passed from the yellow to the red, at the second from the red to the blue, and at the third from the blue to the orange, which he then proceeded to pick up and bring to me. I had noted this same thing in Mr. von Osten's tests, although there, there were often other factors entering in. By exercising the utmost precision in facing the cloths, and by using, in addition, suitable oral signs, I succeeded in getting Hans to bring, successively, each one of the six cloths in the row, and without a single error,—and all this in the presence of Mr. Schillings who did not have the slightest notion of the secret of my success.

We need hardly say, in passing, that all that was true of the tests with colored cloths, was also true of the tests in which the placards were used. It was all the same to the horse whichever was placed before him.

We have thus tested all of the horse's supposed achievements. None of them stood the critical test. It would have been gratifying to have repeated some of the experiments and to have made Hans the object of further psychological investigations, but unfortunately he was no longer at my disposal after the publication of the report of the December-Commission. Some may say that we have had almost enough of a good thing, but we must bear in mind that many of the tests which were carried out,—such as those in which the method was that of "procedure without knowledge", those in which the ear-muffs were used, those in which distractions were introduced,—had previously been made by other persons (see pages [41f], [45], [63]), and with other results, than ours. A more thorough test, therefore, would have been doubly desirable.

FOOTNOTES:

[G] The expressions questioner and experimenter are used interchangeably in this treatise.

[H] Throughout this treatise I am using the word "sign," or "signal," whereas all other writers who have touched upon the Hans-problem, have always spoken of "aids." Following von Sanden,[4] however, I would distinguish clearly between the two. I would designate as aids all immediate stimulations of the horse's body (i. e. by means of contact), which have been designed with reference to the animal's physiological movement-mechanism in such a way that they truly 'aid' him in the production of the required movements. I would regard as signs on the other hand, all stimulations (whether mediate or immediate) which are selected without especial regard to the anatomy or physiology of the horse, and bear no inseparable relation to the thing to be done but are associated with it at the will of the trainer. The rider's use of reins, and control by means of leg-pressure and manner of sitting in the saddle, and the driver's use of the lines,——all these, then are aids. A simple pull at the reins, however, is not an aid, but a sign. The whip may be used for giving signs as well as aids,——the latter, when it does the work of the spur or of the pressure with the knees, as is the case with ladies' riding-horses and in lunging. All calls and all movements of the hand or head merely, on the part of the trainer, are to be regarded as signs.

[I] During the tests Mr. von Osten nearly always wore a slouch hat with a wide rim. The rim, of course, always moved with the head, and made the movements appear on a larger scale, (in the ratio of about 3:2, as I was able to ascertain later by graphic methods). But observation was successful, even at a distance of a meter and a half, when he worked with head uncovered. And even if head and forehead were covered entirely, it was still possible to note the movements by watching the eye-brows. When Mr. Schillings and the rest of us worked with the horse, we either went bare-headed or wore only a very small cap.

[J] For the benefit of those who are familiar with reaction-time experiments of this kind, I would state the following: The reaction to the head-jerk, on account of the minuteness of the latter, was sensory throughout, and therefore all precipitate reactions are entirely wanting. The reaction to the back-step was, like the preceding one, a reaction to a visual cue. (Hans's tapping was almost quite inaudible). Both stop-watches were carefully regulated. In order to eliminate also the constant error which might possibly arise as a result of some difference in the functioning of their pressure-mechanism, the two watches were always exchanged in the different series of tests, by the observer of the man and the observer of the horse. The two time-measurements obtained by the two observers contained, of course, the reaction-times of the observers themselves. In order to equalize the constant error which thereby arose, it was arranged that each observer should react alternately now to the man, now to the horse. In order to be perfectly safe, the reaction-times of those concerned, (von Hornbostel, Pfungst, Schumann and Stumpf), were later determined in the laboratory by means of the carefully regulated Hipp chronoscope. Separate determinations were made of the reactions to the head-jerk and to an imitation of the horse's back-step. Then the time which one observer took to react upon a head-jerk, was compared with the reaction-times of the other observers to the back-step. Since the greatest difference which was found in this comparison, did not exceed one-tenth second, the results obtained in the courtyard required no correction.

[K] See [page 126] on the corresponding reaction-time in the case of man. Similar tests have been made in the case of animals in only one instance, and that for dogs, by E. W. Weyer.[5] But, as might have been expected, they did not yield any satisfactory results.

[L] Mr. Schillings, however, did succeed in making a number of tests with the co-operation of others who had never before worked with the horse. These tests were made under the following conditions: The horse was standing in his stall, when Mr. Schillings and another gentleman approached him. There was no one else present. Mr. Schillings, who tried to remain as passive inwardly, as possible, asked his partner to think consecutively of different numbers between one and 20, which thus were known to him alone. Hans was then commanded by Mr. Schillings to tap the numbers, which he did, to the great astonishment of the men, and especially of Mr. Schillings. In like manner Mr. Sander, a staff physician in the marine, received—so he writes me—three correct responses to four questions which he put to the horse. It happened also in the case of two scientific men and finally, too, in my own case when I first came in contact with the horse, (see [page 88]). The horse's reaction was brought about in the same way in every one of these instances. Mr. Schillings, in bending forward slightly, thereby started the horse a-tapping, and his companion—just as innocently—interrupted the process by means of a movement of his head, when the right number of taps was reached.

I later tried similar experiments together with Mr. Hahn. I was aware of the answer to the riddle at the time, but he was not. Mr. Hahn stepped in front of the horse and thought intently of certain numbers. I did the questioning, that is, I got the horse to tap. In twelve tests Hans responded correctly in only two instances. In the ten others he always tapped beyond the number Mr. Hahn had in mind, e.g., 21 instead of 2, and was evidently awaiting a movement on my part. When we exchanged rôles, Mr. Hahn doing the questioning and I doing the "thinking," the horse would not respond at all, although as a rule Mr. Hahn had been fairly successful in working with him alone. I had gradually gained so much influence over the horse, that he would scarcely attend to any one else when I was about—Mr. von Osten hardly excepted.

In this connection I would prefer to avoid the term "rapport," which may rise in the minds of many, since it has been used so much in connection with the phenomena of hypnotism, for I would not obscure a fact that is clear by giving it a name that is vague.

CHAPTER III

THE AUTHOR'S INTROSPECTIONS

In the preceding chapter we asked: What is it that determines the horse's movements? Independent thinking, or external signs?—We found that it was solely external signs, which we described as certain postures and movements of the questioner. Beyond a doubt these necessary signs were given involuntarily by all the persons involved and without any knowledge on their part that they were giving any such signs. This is to be seen from their statements, which cannot be cavilled at, as well as from the fact that several of them even to-day still doubt the correctness of the explanation which we are here offering. I myself for some time made these involuntary movements quite unwittingly and even after I had discovered the nature of these movements and had thus become enabled to call forth at will all the various responses on the part of the horse, I still succeeded in giving the signs in the earlier naïve involuntary manner. It is not easy, to be sure, to eliminate at once the influence of knowledge and to focus attention with the greatest amount of concentration on the number desired, rather than upon the movement which leads to a successful reaction on the part of the horse. To some this may appear impossible, but those who are accustomed to do work in psychological experimentation, will not deny the possibility of such exclusive concentration upon certain ideas.

If we now ask: "What occurred in the mind of the questioners, while they were giving the signs?", the answer can be found only by way of the process which in psychology is technically called "introspection", i. e. observation of self. In the following we will give the most important results of this process of self-observation, which took place in the same period in which the observations recorded in the preceding chapter were made.

My first experiments were made while the horse was counting or solving arithmetical problems and were as follows: Mr. Schillings, who was alone with me in the horse's barn, asked me to think of several numbers, maintaining that the horse would be able to indicate them correctly upon being asked. He stood to the right of the horse, I stood erect and at the side of Mr. Schillings. There was no one else present. Somewhat skeptical in attitude, I concentrated my mind consecutively on five small numbers. Hans tapped one of them incorrectly, one correctly and three by one unit too many. At the time I considered these attempts as unsuccessful and credited some curious chance with the answers which were correct, or nearly so. This was a mistake, for often during the following days, and in the absence of Mr. von Osten, the horse would give correct answers. Others, of course, would be incorrect, and usually the mistakes would be by one unit,—so that I soon saw that even in the horse's errors there lay some system. It will be seen that Hans responded to me from the very beginning, undoubtedly because I had had the opportunity of watching

Mr. von Osten and Mr. Schillings and had thus patterned my behavior after theirs. I was not at first successful in getting the horse to respond correctly in the case of large numbers. For in order to get complete control over the horse, and, what was, as I later discovered, more to the point, control of myself, some practice was needed. But I was able to work with the horse quite successfully, while I was still in the dark as to my own behavior.

From the very beginning Hans responded as promptly to those questions which I articulated merely inwardly, as to those which were spoken aloud. That all formulation of the question was unnecessary, however, was shown by the following experiments. If, for example, I did not think of any particular number until after the horse had begun to tap, and then fixed upon 5, he would tap 5. If, however, I told him to count to 6, but gave no further thought to the command after he had begun tapping, I would get an entirely wrong response. It was easy to obtain any answer one wished to a question, simply by focussing consciousness, with a great degree of intensity, upon the answer desired. Thus Hans answered my question: "How many angles has a hexagon?", first by 6, then 2, then 27, in accordance with the numbers that came into my mind. The animal always followed the ideas which were in the questioner's mind, and never his words, for it was with the former that the movements upon which the horse depended were bound up.

It was not enough, however, simply to imagine the number desired. It was furthermore necessary that the questioner be conscious of the moment when the horse reached that number. Larger numbers (above 6) were therefore, successful only when every single tap was inwardly counted to the end. The manner of counting was indifferent. Thus I counted 6 as follows: 1, 2, 3, 4, 5, 6, and later: 6, 5, 4, 3, 2, 1, and then again: 6, 6, 6, 6, 6, 6. Finally I used the Greek letters and also nonsense syllables. And in all cases I obtained six taps, the correct response. If, however, I simply counted the taps without knowing when the desired number was reached, the responses were always incorrect, e. g., I counted

In the case of smaller numbers, on the other hand, one often obtained correct results without counting. In this I am borne out by Mr. Schillings. It was merely necessary to image vividly the number 3, or 4, or even the name of a week-day or of a month without the number which would indicate it. In the last of these cases the number corresponding to the day or the month (e. g. 3 for Tuesday, 5 for May, etc.), though not consciously presented, still evidently lay at hand in the subconscious. To use a popular expression, I usually had a "feeling" when Hans had arrived at the right number.

It was furthermore found that it was not only necessary to count to, or to think of, the number desired, but that this must take place with a high degree of tension of expectancy—that is, a strong affective element must enter in. The state required for a successful response was not the mere passive expectation that the horse would tap the number demanded of him nor the wish that he might tap it, but rather the determination that he should do it. An inward "Thou shalt", as it were, was spoken to the horse. This affective state was registered in consciousness in terms of sensation of tension in the musculature of the head and neck, by intraorganic sensations, and finally by a steadily rising feeling of unpleasantness. When the final number was reached, the tension would suddenly be released, and a curious feeling of relaxation would ensue. I have made a series of tests to determine the most favorable degree of tension in expectation. It was possible to distinguish with certainty, three degrees of tension besides the state of utter relaxation,—all of which I measured by means of the differences in the sensations of tension. In cases of tension of the first degree (greatest concentration) the responses were usually correct, a few, however, were lacking by one unit. There was therefore in the latter instance a premature release of inner tension. In cases of tension of the second degree all answers were correct except a very few which were too great by one unit. In cases of tension of the third degree, many answers were wrong, and usually by several units too many. I wished to have the horse tap 10, with the lowest degree of concentration. He tapped 13, then in a repetition of the test, 12. I thereupon increased the tension, Hans then tapped 8. I decreased the tension once more, but so that it was somewhat greater than at first. Hans tapped 10 correctly. At another time I tried to have him tap the number 5, with a low degree of tension. He tapped 6. I intensified expectation and Hans tapped 4. I again decreased it, and he tapped 5, comme il faut. Apparently, therefore, the most favorable degree of tension was one between the first and second,—the latter being the least favorable. After some practice a lesser degree than was used in the beginning sufficed to evoke adequate reactions. The flow of nervous energy to the motor centers of the brain evidently became facilitated through practice. It will be easy to understand why the first days of experimentation caused intense headaches, which later never occurred.

Whenever, in the foregoing, we spoke of a certain degree of concentration which had to be attained, it is not to be understood that the same tension had to be maintained throughout the test, from the horse's first tap to his last. But rather, that it began with a low degree, and gradually increased as the final unit of the count was being approached. It may best be represented by a curve whose maximum represents that degree of tension which we have been discussing. The rise to this maximum which, when attained, was followed by a sudden fall, did not always occur in the same manner. Three types of curve may be distinguished, which were first discovered in purely empirical fashion, and later reproduced voluntarily for purposes of experimentation by diagramming before each test the intricate curve of the varying degrees which the intensity of concentration was to assume. The types may be described as follows:

I. Here the tension curve rises steadily from beginning to end. This type preponderates in the case of small numbers. Thus, when I asked the horse: "How much is 2 plus 4?", the tension increased slowly with every tap from the moment I began counting, until the final tap was reached, when it was again relaxed. Externally this relaxation is noticeable as a slight jerk.

II. In this case the curve does not rise at an equal rate, but rather more slowly at the beginning and later undergoes a sudden increase, or the tension increases immediately at the beginning, remains constant for some time and then ascends to the maximum. This curve is the rule in the case of large numbers and evidently means economy of physical energy, for experience soon taught that a steady increase in tension from the very beginning soon brought it to a level which cannot be long maintained and usually leads to a premature relaxation. In the case of very large numbers the alternation of the slight and the sudden increase may be repeated several times, and at times it may even sink below a level which has already been attained, thus making a wave-like curve.

III. The third type of curve shows a sudden jump between two units at a certain point in its course. This may occur in the case of both small and large numbers but only when the highest or first degree of concentration is employed (see [page 91]). Such a jump frequently occurs in the transition from the tap preceding the last to the last one which is being eagerly expected. Relaxation—with the upward jerk and raising of the head—here occurs at the normal time; Hans taps to the end with his right foot. Oftener still the "jump" described occurs while passing over to the number just before the last. The goal seems within reach and the mental tension relaxes, and with it the physical tension,—the head gives a slight jerk and Hans makes the back-step. Since, however, another tap is still awaited with some degree of tenseness and, since complete erection of the head does not follow immediately upon the jerk of the head, the horse gives another tap with the left foot. Thereupon occurs the complete relaxation of attention, and the assumption of the erect posture on the part of the questioner. That this is psychologically the clue which leads to the final tap, will readily appear from the following remarkable fact: I was able to bring about at will either the back-step with the right foot, or the additional extra tap with the left foot by concentrating the mind either upon the last unit or upon the one just preceding it. In either case the movement which served as stimulus to the horse followed naturally upon concentration on the number. I could of course also control the response by direct voluntary control of the movements involved. Hans thus solved for me the same ten problems first with the back-step, then with the extra final tap.

Finally we will indicate the one true inner cause of the difficulty in getting the number 1 as a response. It is not easy to relax attention immediately after having just begun to concentrate. Relaxation, therefore, often occurs with a certain retardation, and the result is a belated jerk of the head.

Briefly, I would also mention a few of the more interesting introspective observations which were made in situations in which the horse responded with movements of the head for answers such as "yes" and "no", "up" and "down", etc. From the very beginning I put questions to Hans which would have to be answered by a shake of the head. It often happened that instead of indicating "0", Hans would begin tapping some number. But the wonder of it was that, in many cases, he responded properly. I knew only that I inwardly pronounced the word "null" (zero), and that I looked expectantly at the horse's head. In the case of questions to which I expected the answer "yes" or "no", I imagined myself enunciating the answer, i. e., I used motor imagery. The tests failed, the moment I employed only visual or auditory imagery, whereas, motor imagery was always effective in calling forth correct reactions.[M] When the proper response was "up" and "down" I would think of those directions in space, and likewise with "left" and "right" in which case also I would put myself in the horse's place.

While I was still ignorant of the nature of the necessary movements, the tests were successful only when I had put the question aloud or in a whisper, but never when I failed to enunciate, i. e., when I merely had the question in mind ("in idea"). But this also became possible after a little practice, although I could not then give an explanation for my success. Except in one instance, we could discern no difference between problems spoken and those merely conceived by Mr. von Osten who had had the advantage of long practice. But the one exception deserves mention. The old gentleman commissioned Hans, presumably without uttering a word, to step backward to the left. Hans thereupon responded by giving his entire repertoire, as follows: He moved his head to the right, then to the left. Then he leaped forward and repeated the same movement of the head. Hereupon he stepped backward and signified a "yes" by a movement of the head. He then lowered his head and made two leaps forward. After this performance Mr. von Osten repeated the same command aloud, and in every case Hans responded properly. Again the silent command was given and again the horse responded with the series of reactions described above, lowering his head leaping forward, etc. In this experiment, without exception, the spoken command evoked adequate reactions,—the silent command, an incorrect response. Evidently the impulse to movement was not so great with the mere conceiving of "right", "left", etc., as when the words were enunciated. It, therefore, required some practice on my part before a sufficiently strong movement-impulse became associated with the idea. All this is in no wise at variance with the fact that tests involving counting and computation were as successful when the problem was given in silence, as when it was spoken. The signs for tapping, viz.: inclination and erection of the head and body, followed the question. The question therefore became superfluous. On the other hand the signs for head-movements on the part of the horse, were given while the question was being put. I ask, which way is "upward", and at the same time I look upward. In this case therefore the question itself is not entirely insignificant.—I experienced greater difficulty in getting Hans to respond with the head-movement to the left. After much practice I was able to evoke this movement by means of giving the command aloud, but never by means of the "silent" command. Accidentally I hit upon a device by means of which I attained this end also. I asked the horse aloud "Which direction is left?",—whereupon he reacted properly; then I immediately repeated the question silently, and was successful every time. My mental attitude here was still the same as when I put the question aloud. What sort of an attitude this was, I could not, of course, have stated explicitly at the time. I could not, therefore, awaken it at will,—and if I allowed but a minute to elapse between the spoken and the silent question, the vivid after-effect (the so-called "primary memory image") soon disappeared and the test was wholly unsuccessful. Practice, however, soon helped me to overcome this last difficulty also. I believe that my inability to evoke this specific reaction on the part of the horse, lay in the unfavorable position which I assumed, for it did not allow the horse to

perceive my movements easily. For the same reason, Hans would at first indicate "no" and "zero" by turning to the right, seldom to the left.

As in the case of counting, a high degree of concentration was also necessary here, but with this difference, that here attention was directed to ideas present to the mind, ("yes", "no", etc.), whereas in the counting process attention was directed toward expected sensory impressions (i. e., the taps of the horse).

All that has been said thus far is readily understood psychologically. The following curious fact, however, is noteworthy. Hans used the head-movement to indicate two such different concepts as "zero" and "no"; it appeared therefore that in both cases he was receiving the same kind of directive. Observation proved that such was the case and the directive in question was none other than an imitation in miniature, or rather a movement anticipatory of the expected head-movement of the horse. Now, whereas the signs for "up", "down", "right", and "left" were natural expressive movements which are normally associated with the corresponding concepts, this cannot be said to be true of "no" and "zero". My laboratory observations (see [page 107]) lead me to conclude that the movements, by means of which the concepts "no" and "zero" are naturally expressed, are quite different; and neither of these corresponds to the signs for "zero" and "no" which the questioner involuntarily gave to Hans. What was the genesis of these unnatural forms of expression? If we might assume that the questioner always had in mind the movement he awaited on the part of the horse, and never thought of "zero" or "no", then the contradiction would solve itself. But I must deny decidedly that I ever thought of the movements of the horse's head, and Mr. Schillings, whom I questioned on this point, agreed with me in this, in so far as his own mental processes were concerned. I can see nothing for it but that in this instance the expressive movements normally connected with the concepts "zero" and "no" have been replaced by other forms, without the questioner becoming aware of it. That such displacements may occur, has been shown by the tests described on pages [107] to [112]. That they did occur in this instance may be concluded from the following observation. In responding to me, as well as to Mr. Schillings, Hans always moved his head first to the left, then to the right, never in the opposite order. That this was not a peculiarity of the horse, but must be ascribed to the signs which were given him, is shown by the possibility of inverting the order under experimental control ([page 77]). Frequently Mr. Schillings and I had seen the horse respond to his master by means of such head-movements, and the order was always, without exception, the one mentioned. It must be assumed therefore that the horse's movement, which we so often noticed, made such an impression upon us, that afterwards it was regularly reproduced on our part quite unconsciously, so that Mr. Schillings never, and I only after a long time, became aware of the whole process.

In closing, just a word as to the discovery of our own movements. I soon noticed that every pronounced raising of the head or trunk brought about an interruption in the horse's response. But only by observing the final movement in the case of Mr. von Osten did I discover that I, too, performed a slight erection of the head. Observation of others was less difficult than the observation of one'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.

FOOTNOTES:

[M] Thus it is possible to think of the word "no" in three different ways. I may get a visual image of the written or printed word, or the auditory image of the word as spoken by another person, or finally I might think of it in terms of images of the sensations of movement which would arise if I myself were to enunciate or write the word. And so, in like manner, I could think of any other word in terms of either visual or auditory or motor imagery. In all probability the auditory and motor always occur together,[6] but still it is possible to make the one or the other predominate.

It appears that the imagery of most persons is a mixture of auditory-motor and visual elements, with a predominance of one or the other kind. Individuals who utilize almost exclusively the visual (as does the author, as a rule), are rare. But rarer still is the pronounced motor type.

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 individuals,—and secondly, to ascertain in how far the psychical processes which I had noted in my own case and which I believed to lie at bottom of these movements, were paralleled in, and confirmed by, the introspections of others. The effort was made to make the experimental conditions as nearly as possible like those under which the horse had worked. The affective atmosphere which colored the situations in which the horse took part, could not, of course, be transferred, but this was in some respects an advantage. One person undertook the rôle of questioner, another—myself—that of the horse. The experiments fall into three groups, corresponding to the types of the horse's reactions: 1, tests in counting and computation; 2, tests in space reactions; 3, tests in fetching or designating objects.

In the experiments in counting and computation, the questioner, standing at my right, thought with a high degree of concentration of some number (usually between 1 and 10, but sometimes also as high as 100), or of some simple problem in addition. Then I would begin to tap,—but in human fashion with my right hand, rather than with my foot—and continued until I believed that I had perceived a final signal. I thus tested, all in all, twenty-five persons, of every age and sex (including children of five and six years), differing also in nationality and occupation. None of them was aware of the purpose of the experiments. It could not escape them, to be sure, that they were being watched. It was also evident to them that the things noted were certain tensions and movements; but none of my subjects discovered what the particular phenomena were that I was looking for. Only in a few isolated instances did they report that they were conscious of any movements on their part. With the exception of two persons, they all made the same involuntary movements which were described in [chapter II], the most important of which was the sudden slight upward jerk of the head when the final number was reached. It was at once evident that the direction of this jerk depended upon the position which one had asked the subject to assume at the beginning of the test, the direction changing whenever the position was changed. Thus, if the subject stood with head bowed—the body either being held erect or likewise bowed,—then release of tension would be expressed physically by an upward jerk. (Occasionally the entire trunk is slightly raised, so that it was possible to observe this physical reaction when standing behind the subject). If the subject had bent his head backward, the "psychological moment" was marked by a forward movement, (although under certain conditions the head was, in such a case, observed to bend still farther backward). If during the tests the head was bent slightly to the right, then the reaction was expressed in a movement toward the left, and vice versa, if it had been on the left, it was bent to the right. If the subject had been bending his head forward and to the right, he then raised it upward and to the left, etc. In all of these changes of position I noticed an intermediate posture which, to be sure, it was not always an easy matter to discover,—viz.: an upright position in which there was discernible no manner of head-movement or only a slight tremor. If the subject was lying on his back with his head supported, then there was noticeable a very slight movement to one side. In this same way a number of other positions were tested in order to discover for each the characteristic movement expressive of release of tension. It would therefore appear that the raising of the questioner's head, which served as the signal for stopping for Mr. von Osten's horse, was but one instance of a general law which may perhaps be stated thus: The release of muscular tension which occurs with the cessation of psychic tension, tends to bring about that position of the head (and body) which, at the time, represents the slightest amount of muscular strain.—These movements seldom were pronounced enough to be compared to motion through a distance of one millimeter, in a very few cases only did they attain to the magnitude of one or two millimeters: I failed to note them entirely, however, in only two individuals, two scientific men whose mode of thought was always the most abstract, and one of these was, in spite of repeated attempts, unable to elicit any response whatever on the part of the horse.

In the cases of the more suitable subjects I was able to indicate not only the number they had in mind, but also the divisions in which the number was thought, thus 12 as 5 and 5 and 2, or the same number as 2 and 5 and 5, and I was also able to determine the addends in the addition—i. e., whether the problem had been conceived as 3+2=5 or as 2+3=5. It frequently happened that in the beginning I would sometimes mistake these subdivisions, which were recognizable by the less pronounced jerks, for the final number. Thus I would often respond with 4 instead of 8, or 3 instead of 9, or with 3 when the problem was 3+2, just as Hans had so often done. In these tests, too, the difficulty of getting the number 1, as well as the larger numbers, came to light. Thus three times in succession 17 was indicated as 4, as 9, and as 17. But after some practice I was able to give numbers as high as 58 and 96. The frequency of the errors of one unit too many and of one unit too few is also noticeable in these tests.

We also found desirable corroboration, by trustworthy subjects, of the introspective observations of the author, which were reported in [Chapter III], with regard to the significance of concentration and the curve of attention. It is hardly necessary to mention that no attempts were made to influence the subjects in their accounts by asking suggestive questions. The most valuable feature about these tests was that the mute horse had now been replaced, as it were, by an animal capable of speech, and that it was now possible to follow the same process both from within and from without. Two illustrations may be welcome. The one who took the part of the horse gave three taps and made the following entry: "At 3 I saw a slight upward jerk of the head on the part of the questioner". The questioner however had thought of 4, and made the following note, without knowledge of the other's entry: "I was aware of extreme tension, so that it was impossible for me to get beyond 3". Or again, the 'horse', reacting to a movement on the part of the questioner, stopped at 3, but the latter, having intended to obtain 2, made the following entry: "I noted clearly that I ceased thinking of the number too late, and did not put on the brakes, as it were, until I had arrived at 3". We see that errors here were entirely the fault of the questioner, just as had been the case in the tests with Hans. (See [page 151f.]).

In a second group of experiments I asked a subject to fix his mind upon certain concepts, such as "up", or "down", "right" or "left", "yes" or "no", and others, in any order he pleased, but with the greatest possible degree of concentration. The subject each time had the choice of four or six concepts, and he was told to think of one of them at the signal "Now!". How he was to 'think' the concept was left entirely to him. He was also told to interpolate the series with a 'blank', that is, to think of nothing at all. Standing opposite the subject, I tried to guess at the mental content of the person's mind, on the basis of expressive movements. Sometimes I reacted by shaking or nodding the head, etc., just as Hans had done, but as a rule I was content to say the word which I thought the subject had in mind. With twelve subjects (a total of 350 tests) I made an average of 73% correct responses, and in the more favorable cases I attained even 90 to 100% correct responses. Very slight involuntary movements of the head and eyes, which showed but little individual variation, and always occurred when the subject began to fix upon the concept, were the signs which I used as cues. As in the case of the movements expressive of the release of tension, which I discussed above, these movements, too, occurred without the subject being aware of them, (except in those rare cases in which they had once or twice been especially pronounced). Indeed, it was very difficult and in some cases almost impossible for those persons whom I had initiated into the secret, to inhibit them voluntarily. "Up" and "down", "right" and "left", were expressed by movements of head or eye in those directions, "forward" by a forward movement of the head, "back" by a corresponding movement. "Yes" was accompanied by a slight nod of the head; "no" by two to four rapid turnings of the head to either side.[N] "Zero" was expressed by a movement of the head describing an oval in the air. Indeed, it was even possible to discover whether the subject had conceived of a printed or a written zero, for the characteristics of both were revealed in the head-movements. I was able later to verify this graphically. With Ch. as subject, I made 70% correct interpretations in a total of 20 tests; with von A. as subject, 72% in a total of 25 tests. And finally I was able to interpret the signs without any errors at all. It was not absolutely necessary to look directly at the subject's face. Even though I focussed a point quite to one side, so that the image of the subject's face would fall upon a peripheral portion of my retina, I still was able to make 89% correct interpretations in a total of 20 tests.—This is not astonishing after all, when we recall that the periphery of the retina possesses a relatively high sensitivity for movement impressions, although its chromatic sensitivity is very low.[O]

It was assumed, as indicated on [page 99], that in the case of Mr. Schillings and myself the movements naturally expressive of "zero" and "no" had been displaced—without our being aware of the fact—by others, viz.: those which the horse required as directives for his reactions. Since this was the case, we tried to discover if a similar displacement could be brought about experimentally. The attempt was successful and we discovered that under suitable conditions we could cause the subject—quite without knowledge on his part,—to establish an "association" between any given concept and any given expressive movement. The following experimental series will serve to illustrate this fact.

I had one of the subjects (von A.) think of "left" and "right" in any order he chose. (The command was purposely given only in a general way: "Think of 'right' or 'left'".). We had agreed that I was to try to guess the mental content of the subject's mind, but I was not to utter a word. Instead, I was to indicate "right" in every case by an arm movement downward, and "left" by a movement upward. To the subject I gave a fictitious but plausible reason for all this. The behavior of the subject took the following course: In the first three tests he moved his eyes to the right when he thought of "right", and to the left when he thought of "left". This was the normal expressive movement. In the fourth test, however, the thought "left" was accompanied by an upward movement of the eyes. Two further tests again showed eye-movements to the right and left. In the seventh test with the idea "left" the eyes moved first to the left and then immediately upward. In the following ten tests the eyes were turned regularly upward at the thought of "left", and downward at the thought of "right", with only one exception which was a normal movement to the left. The normal expressive movements, therefore, were displaced by the artificial, after the seventh test.

In the case of another subject (B.) in whom normally the thought of "up" was accompanied by a slight raising of the head, and "down" by a downward movement, these natural forms of expression disappeared entirely as a result of my arm movements to the right to indicate that I inferred his having in mind the thought of "up", and to the left when I inferred that he was thinking of "down". Instead, there appeared not merely the desired movements to the right and left, but rather movements upward to the right and downward to the left. That is, instead of a complete displacement of the old by the new, there occurred a combination of the two.

A third type of result appeared in still another subject (Ch.), who normally expressed the concepts "right" and "left" by eye or head movements (never both kinds at the same time) to the right and left. Here my arm movements up and down caused the eye and head movements to be made simultaneously, so that the thought of "right" found expression in an upward movement of the head and an eye movement to the right, and the idea of "left" in a downward head movement and a movement of the eye to the left. The subject had no knowledge of this process, and it took six tests to bring about the new reaction. From that point onward the new movements were so well established that, depending upon them for my cue, I was able to make 32 correct inferences in a total of 40 tests. During the latter part of this series I blindfolded the subject, so that I could not see the movements of his eyes, and therefore had to base my inference entirely upon his head movements.—After removing the bandage, at the end of the series, I told the subject that I would go through another series, in which I intended to indicate his thought of "right" by an arm movement downward (instead of upward as heretofore), and his thought of "left" by a movement upward. (This he regarded as an idle whim of mine). It was only after the twelfth test that the former "association" which I myself had caused to be established, was completely displaced by the new. The thought of "right" was now accompanied by an eye movement to the right and instead of a raising there was a lowering of the head. A corresponding change occurred in the head movement expressive of the thought of "left". These responses were occasionally varied by some in which only the head movement or only the eye movement occurred. But these movements were always to the right, or downward and to the right, at the thought of "right",—and to the left, or upward and to the left, at the thought of "left". In ten tests I made ten correct inferences. After the new association appeared firmly established, I ceased responding by means of arm movements, and indicated my 'guesses' by word of mouth. At first the newly acquired movements continued to appear promptly in the subjects. But gradually they tended to become more uncertain and finally disappeared, as readily as they had appeared, and the normal conditions were once more established. Nor was there any tendency to reappear on the following day in another series of tests. (Those just described had been made on one day in the course of an hour or two). But as soon as I again used the earlier method of arm movement to indicate my inferences (raising the arm for "right", lowering it for "left"), the former artificial association was again established, although not until some 14 tests had been made,—during which the normal movements to the right and left were often inhibited and during which the conditions were, on the whole, chaotic. The new association, thus re-established, remained constant during the ten tests of the remainder of the series, but has very probably again disappeared long ere this. In the case of this subject it appears therefore that the new associations were superimposed upon, but in no sense displaced, the normal expressive movements. Nor did the two coalesce (except in a few exceptional cases), but tended as a rule to occur independently of one another.

I would emphasize once more that none of the subjects had any knowledge of the purpose or meaning of the experiments. Also, I was convinced by questioning the subjects afterwards that none of them—and this is the essential point—had merely conceived of the arm movement which they were expecting me to make, instead of concentrating thought upon the idea of "right" or "left". On the contrary, all of them considered my particular movements mere vagaries and without purpose, and they felt perfectly certain that they were in no wise influenced by these movements. Also, none of the subjects was conscious of any movements on their part, except one, who was at times aware of her eye movements to the right, but never of those to the left, (see [page 111]), nor of the head movements which for us constituted the phenomena of prime interest. When I asked my subjects what they believed to be the cue upon which I based my inferences, they invariably responded with probable explanations which were always wide of the mark, and those to whom I disclosed the cue—(after the experiments were completed), were thoroughly astonished.

In the tests just described we had to do only with such ideas or concepts as normally were associated with some stereotyped form of expressive movement (see [page 106]). I now chose a group of ideas which are not normally associated with a particular form of motor expression peculiarly characteristic of them, and sought to establish artificially such a connection with some arbitrary movement, without consciousness of the process on the part of the subject. Thus I asked one subject (Miss St.), who had no intimation of the aim of the tests, to think of the following words in any order she might choose: "Ibis" (ibis), "Irbis" (panther), "Kiebitz" (plover) and "Kürbis" (pumpkin). I said that I would react to her thoughts by means of arm movements forward and backward to the right and to the left, respectively. 15 out of 20 tests were successful, without the slightest suspicion on the part of the subject (whose whole attention was concentrated on the word-content), that she was giving me the necessary directives in the form of very minute movements of the head and eyes to the right and left, etc. She was greatly astonished that I should be able to guess words so much alike,—(she did not know that the element of likeness was productive of no difficulty). When, during one of the tests, the subject happened to think spontaneously of the movement she was expecting me to make, she became confused, and as a result the number of my sucessful reactions suddenly fell. I never would have discovered the cause, had not the subject enlightened me without my asking.

I repeated this series with three other persons, who had had some psychological training. I did not use the same movement for each word in all three cases, but indicated the word "Kiebitz", for instance, by means of an upward movement in one case, by turning the head to the right in another, etc. In one of the three cases the tests were almost wholly unsuccessful. The cause for this came to light later, but it would involve too much exposition to discuss it at this point. In the case of the other two persons, the tests were successful beyond expectation. I had made my various arm movements only a few times when they presently began to raise their heads slightly when thinking of "Irbis", and to move it to the right at the thought of "Kürbis", etc. In the two series of 35 tests I did not have a single error. In a number of instances I succeeded in guessing the word upon which the subject had decided, even before the test proper was entered upon—i. e., before the signal for concentration had been given. Nothing surprised a subject more than the remark: "You are intending to think of the word 'Kürbis'", or "You had thought of concentrating your mind upon 'Ibis' but later decided in favor of 'Kiebitz'", yet nothing could be more simple. Before every test the subject would consider what word he would fix upon, and while he was saying to himself "I will choose 'Ibis'", the proper movement would accompany his decision, although it was only very slight, because attention had not yet attained the degree of concentration which was employed in the test proper.

In these experiments also, the subjects, whom I know to be absolutely trustworthy, declared that they never thought of the arm movements which I was to make. They regarded them as being quite irrelevant. Also—with but one exception—they thought of the objects, in so far as they imaged them visually, as being directly before them, and not off in the direction indicated by my arm movements. Thus they did not image the plover ("Kiebitz") as being on the wing, when I raised my arm, or as resting on the ground, when I pointed downward, etc. One of the subjects had done this occasionally, but by no means regularly. He was therefore asked to localize all objects in the same place, i. e., directly in front of him at the level of the eye. He complied with this request, but no change, whatever, was observed to occur in his expressive movements.

In order to overcome the difficulty just mentioned, I selected another subject (Miss von L.), whose power of visualizing was very slight, and requested her to fix her mind upon four words which I had selected because they were not, necessarily, associated with a particular image. The order in which the words were to be thought of, was entirely optional on her part. The words were "Form",

"Inhalt", "Mass", and "Zahl", (form, content, measure, and number), and each of them I accompanied, with a certain definite arm movement. The subject always pronounced the word inwardly as emphatically as possible, but without ever imaging the corresponding arm movement. Often, it must be noted, she did not know whether or not the movement which I made was the proper one. And yet she, too, soon fell into line in the matter of executing unconsciously the characteristic head movements. In a total of 50 tests, I was able to make 10 correct guesses in the course of the first 20 tests, 8 in the next 10 tests, and 19 in the last 20 tests. Miss von L. noted only a few of her upward head-movements, viz.: those that were especially pronounced (movements through about 2 millimeters), but of the others she knew nothing. The same experiment was repeated with a psychologist, well-trained in introspection, as a subject. Success was even greater here. But no matter how closely the subject observed himself, he was unable to solve the puzzle.

Variations which were introduced in these tests, I will only mention in passing. Thus, instead of making an arm movement, I, in some cases, would tap with my foot, for "Ibis" once, for "Kiebitz" twice. The subject could not see my feet. The involuntary movement-expression which became associated with "Ibis" was one nod of the head, with "Kiebitz" two nods, etc. Here our only

concern was to show that unconscious change in natural expressive movements and the acquisition of artificial ones are possible in the case of psychically normal subjects trained in introspection.

I was not satisfied with convincing myself subjectively of the facts indicated, but sought to fix them objectively, by means of a graphic method. For this purpose I used the device mentioned by Prof. R. Sommer for the analysis of expressive movements.[18] The purpose for which Prof. Sommer's apparatus had been constructed, was to record the involuntary tremor and movement of the hand. These movements, of course, take place in the three dimensions of space. By means of three levers it is possible to record the movements upon the flat surface of a smoked paper fastened to the revolving drum of the kymograph, the movements in each direction being recorded by a separate lever, in such a way that the three curves thus made represent the analysis of a single movement into its three dimensional components. By making slight changes, which tended to complicate the experiment somewhat, I adapted the apparatus to the measurement of movements of the head. The method of experimentation was the following. The subject whose movements were to be registered, was placed in the device in such a way that his trunk and head were bent slightly forward, the latter a little more than the former. 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 that pressure upon the keys closed two electric circuits and, releasing the keys, opened them, and both the closing and the opening were recorded upon the smoked paper by means of the markers. And, finally, in order to ascertain the time relations of all these processes, a time-marker indicated the time in fifth-seconds upon the revolving kymograph record. The time-curve was recorded just below the other curves.

Of the curves[P] thus obtained under the most equable conditions possible, we publish seven which show the great general uniformity of the tests made upon the horse with those made in the laboratory. The rôle of questioner was undertaken at different times by Mr. Schillings and the students of philosophy, Messrs. von Allesch, Chaym and K. Zoege von Manteuffel. To all of them I am greatly indebted for their unselfish services in these laborious tests. The experiments with von Allesch and Chaym, who were among the most suitable of my subjects, were conducted absolutely without knowledge on their part of the nature of the phenomena which I was observing. Neither of them knew anything about the expressive movements in which they were unconsciously indulging, and furthermore, since they kept their heads bowed during the entire course of these experiments, they did not perceive what it was that I was observing. It is interesting to note that Chaym on the occasion of his only visit to the horse, immediately received a number of correct responses. Without a doubt von Allesch would have met with equal success. The other two subjects (von M. and Sch.) went through this series of tests, possessing some knowledge of the nature of the movements involved. Conditions were such that they (and especially Mr. Schillings) could not be prevented from obtaining some knowledge of the essentials, at least. However, it would be wrong to suppose that for this reason the results were more favorable, owing, mayhap, to voluntary efforts on the part of the subject. The contrary was true. The two subjects who had no knowledge of the character of the reactions upon which my responses depended, retained their normal habits, unchanged, throughout the series,—whereas the last-named two, afraid lest their knowledge vitiate the result, lost more and more of their power of concentration and within a short time were in a condition of tense inhibition, which is all the more conceivable, since they had had no psychological training whatever.[Q]

Their movements, which at first were quite profuse, decreased more and more, so that in the case of von Manteuffel the percentage of my successful responses sank from 73% correct responses in 90 tests to 20% in a total of 20 tests,—and in the case of Schillings from 75-100% to 23% in a series of 35 tests. The curves obtained with von Manteuffel as subject, which I am here publishing (figures [8] and [15]), are, however, true to his normal habits. The same is true of the two first curves of Schillings (figures [10] and [11]), whereas the third ([figure 12]) shows distinctly the traces of the state of inhibition into which he fell, and represents the same condition as when Mr. Schillings, while preoccupied, tried to work with Hans. All the finer details of the phenomena in question, were likewise unknown to these two subjects.

For purposes of a clearer understanding of the various curves, [figure 5] is inserted to give the general scheme of their arrangement.