Chapter 5 EXPLANATION OF THE OBSERVATIONS

The author having described the observations made upon the horse, and having discussed the activities of the questioner upon the basis of observations made objectively and upon his own introspections, and having verified the results thus obtained, by means of laboratory tests,-we are now in a position to solve satisfactorily all the problems which this interesting case has presented.

That which is least difficult to understand is the horse's seeming knowledge of language and particularly his ability to answer questions, no matter by whom, or in what dialect, they were put. As a matter of fact, it made no difference who desired an answer, for the only person upon whom the experiment depended was the questioner, that is, the one who asked the horse to tap. We have everywhere designated this person as the experimenter or questioner. It was he who gave the directions, and since all that were involved were visual signs, the drama in which Hans appeared as the hero, was nothing but a pantomime. All speech was superfluous and, except in so far as the tone of voice in which it was spoken was soothing or reprimanding, it was quite unintelligible to the horse.

From the foregoing, the reader understands without further explanation Hans's ability to count and to make computations. If the number of taps had depended solely upon the length of time and the angle at which the questioner bent forward, the horse would have been able to tap any number desired. Since, however, only the right foot was employed, the left one being used at most for making a final tap, the number of taps had an upper limit which was due to the fatigue of the animal. This limit was about 100. That it was possible to ask such questions as: "How many times is 100,000 contained in 654321?", and thus to give problems involving millions, is perfectly clear.

All wonderful feats of counting and computation which were accomplished while thus experimenting with the horse are to be accredited, not to the horse, but to the questioner. If such is the case, they certainly cannot be considered astonishing. Thus, when to the question, "How many of the gentlemen present are wearing straw hats?" the horse answers correctly in accordance with the wording of the question and omits the straw hat of a lady, then Mr. von Osten is the guide. It is no wonder that Hans never showed the slightest excitement when confronted with difficult problems, nor that it apparently took no time whatever to solve them.

Hans, however, was also a faithful mirror of all the errors of the questioner. Aside from mistakes due to occasional interruptions on the part of visitors, these errors had two sources: faulty computation and inadequate concentration-i. e., aside from arithmetical errors on the part of the questioner, were his premature or belated movements. Since both of these factors might be operative, the following three possibilities arise.

(a) The questioner computes correctly but does not move at the proper moment. Nearly all the errors which had been accredited to the horse, were of this kind.

A part of these errors had the appearance of being significant, that is, they might be interpreted as a misapprehension of the question. If, for instance, instead of a sum only one of the quantities was given, or, if instead of a product only one of the factors was given, it might be interpreted that the horse simply wished to repeat the problem. Thus, Mr. von Osten in response to the question: "How much is 3 times 5?", twice in succession received the answer, "3", and upon my question, "How much is 3 plus 4?" he answered, "3", and to "How much is 2 times 6?" he tapped 6, and to "What is one-fourth of 36?" 4. In part (certainly in the second and third example cited) an individual quantity or factor had been emphasized in the consciousness of the questioner (cf. page 105) and in part the reactions were due to chance. Thus, when Mr. Hahn asked the question: "What is one-half of 10?", he received the following responses: 2 and 10, and then 17 and 3. To this class belong also, the tests made by the Commission of September and reported in Supplement III. (See page 255).

Other errors, even though they may not have appeared to be significant, might yet have been characterized as mistakes due to speed; as when, e. g., Hans made an error of one unit-and sometimes, though less frequently, of two units-too much or too little in his response. One might be led to believe that Hans had not made an error of calculation but merely of counting in the process of giving his result, which always had to be done by the cumbersome method of tapping. As a matter of fact, the trouble lay in the wrong degree of concentration on the part of the questioner: In errors of +1, tension was too slight, in those of -1, it was too great (see page 91). This comes out clearly in a comparison of the two more extensive series which I took in the case of Mr. Schillings. During the first series, he was well disposed, and was able to concentrate effectively, while during the second, he was nervous and easily diverted. This difference in intensity of concentration in the case of the two series is attested, not only subjectively by Mr. Schillings's introspective statement, but may be measured objectively by means of the number of final taps which the horse gave with his left foot during these two series. We saw (page 94) that these final taps were always a sign of intense concentration and, as a matter of fact, one-half of the horse's responses to Mr. Schillings during the first series were made in this way; whereas, in the second series, only one-third were of this sort. (I, myself, was never able to get, without conscious control, a greater number of this type of response.) We may therefore say that, in the first series we had a high degree of tension, or concentration, whereas, in the second series, we had a low degree. The errors distribute themselves over the two series as follows:

+1 +2 -1 -2

Series I (31 tests)

Correct responses : 87%

Incorrect " : 0% 0% 13% 0%

Series II (40 tests)

Correct responses : 40%

Incorrect " : 40% 8% 2.5% 0% (and 9.5%

other kinds of errors.)

We find in Series I no "+1" errors, but only "-1" errors; in series II, on the other hand, the errors are almost exclusively of the "+1" category, equaling the number of correct responses, and there is only one "-1" error. A series obtained in the case of Mr. von Osten is almost as satisfactory an illustration. When he first began to take part in tests in which the procedure was the one we characterized as "without knowledge" and had to note their complete failure, he was thrown into such confusion that the responses in the case of procedure with knowledge were also incorrect. The errors there were always +1, (whereas those in the case of procedure with knowledge, which were due to quite different causes, were very great and inconstant.) The number of +1 errors obtained on this occasion comprises one-fourth of all the plus errors which were ever obtained in the case of Mr. von Osten during the entire course of these experiments. Finally, I would mention two examples of my own. In the course of my very first attempts with Hans I obtained, as I said on page 89, three responses in a total of five which exceeded the correct result by 1. This I would explain by the fact that although I employed a high degree of concentration, I nevertheless was somewhat skeptical. The result was a certain deficiency in the degree of concentration. A second example which I would cite is taken from the period in which I had already discovered the cue to Hans's reactions and goes to show that I was then still able to eliminate the influence of this knowledge and to work ingenuously. To the question, "How much is 9 less 1?" I, momentarily indisposed, received the answer 10, and then six times in succession the answer "9", and finally the correct response, "8".

Errors of another kind-the not infrequent offenses against the very elements of counting and the fundamental arithmetical processes-were regarded in part as intentional jokes and by an authority in pedagogy as a "sign of independence and stubbornness which might also be called humor". Hans emphatically asserted that 2+2 was 3 or he would answer questions given in immediate succession as follows: "How many eyes have you?"-2. "How many ears?"-2. "How many tails?"-2. These errors, as a matter of fact, evince neither wit nor humor, but prove incontrovertibly that Hans had not even mastered the fundamentals.

Many of the errors baffle every charitable attempt at interpretation. These gave the horse the reputation of capriciousness and unreliability. If Hans designated the tone "e" as the seventeenth, or "g" as the eleventh, or when he called Friday the 35th day of the week or believed 50 pfennige to be worth only 48, the cause for these responses lay either in the insufficient degree of tension on the part of the questioner (as in the first three examples) or in the extravagant expenditure of the same (as in the last case). If, therefore, the horse at times would "hopelessly flounder" which would seem to be indicated by tapping now with the right and now with the left foot, then as a matter of fact, this form of reaction came about as was described on page 61, with this difference that there we had to do with voluntary controlled movements on the part of the questioner, whereas here, they are the result of an unsuitable degree of tension which expressed itself in frequent and disconcerting jerks. Besides the answer 3, this so-called floundering was the only reaction the average person could obtain from the horse in the absence of Mr. von Osten and Mr. Schillings. It would however occur also in the case of these gentlemen and would be received by them with resentment when in truth it was Hans's greatest feat, for he showed his extremely keen reaction upon every movement of the questioner. To this group belong also the errors in the case of higher numbers, the sole cause of which lay in the difficulty with which tension could be maintained and the body kept motionless for so long a period. These errors occurred in accordance with a certain law. If, for instance, a certain test repeatedly evoked incorrect responses, the questioner would gradually increase the duration of tension and would thus come a little nearer to the desired goal with every test. In this way, Mr. von Osten desiring 30 as an answer obtained consecutively the responses, 25, 28, 30; and I, myself, for the answer 20, received consecutively the responses 10, 18, 20 (see also the laboratory tests, page 105). Sometimes too, the questioner would flag in his efforts before the goal was reached. Thus in one of my first tests, I received for the answer 11 the following responses: 1, 4, 5, 7, 4. I was unable to get beyond 7. In other instances, the horse responded first with too few and then with too many taps. The correct response therefore could only be obtained after an appreciable amount of gauging of tension, as in target practice there must be a gauging of distance. (See page 92). In this way Mr. von Osten obtained for 10 the responses 8, 8, 11, 10, and Mr. Schillings for 17, received 9, 16, 19, 18, 18, 14, 9, 9, and finally, after some efforts, 17 taps. Thus there was a rise from 9 to 19, then a fall back to 9 and after eight tests the correct response. As long as we attempt to explain this fact as error on the part of the horse, so long will it remain inexplicable, but the moment we regard it from the point of view of the psychology of the tension of expectation, it becomes perfectly plain.

The same holds true for the curious predilection which Hans appeared to have for the numbers from 2 to 4, especially for 3 (see page 68). As a matter of fact the cause of this lies in nothing other than the inadequate concentration of attention on the part of the questioner and less often in an extravagant expenditure of concentration, which explodes immediately after the first tap on the part of Hans (as in the case of my first tests); but usually the cause lay in a complete lack of concentration, though the same result may be produced by various causes. It is usually after 2 to 4 taps of the horse's foot that the questioner, who does not concentrate, makes his first move which naturally puts an end to the tapping on the part of the horse. As a rule this jerk follows immediately upon the second tap. (On the other hand, relaxation of attention is very difficult upon the first tap. See page 95). The questioner, however, would expect further tapping and therefore would not bring his body back to a completely erect position and the result would be a 3, the last unit of which would be given by the final tap with the left foot. Here we also obtained light as to the answers which Hans gave in those tests in which the method was that of "procedure without knowledge". These responses had nothing to do with the problem, for neither the horse nor any one else knew the solution. But in the horse's responses the degree of tension of the questioner's concentration was faithfully mirrored. An experimenter who was as skillful in concentrating as Mr. von Osten, obtained-almost without exception-very high numbers, whereas one whose concentration was slight would receive in response to nearly all questions the answers 2, 3 or 4. Thus, the Count zu Castell received in response to seventeen questions the answer 2, three times, the answer 3, six times, and the answer 4, four times, two answers being accidentally correct.

Another group of errors was characterized as stubbornness on the part of Hans, such as his persistence in repeating an incorrect response, or his repetition of a former correct answer in response to later questions where it was perfectly senseless. During a demonstration before a large number of persons, I held a slate with the number 13 upon it within the horse's view and also within view of the spectators. I, myself, did not know what number was written on the slate. Having been asked to tap the number, Hans responded by tapping 5. The grand-stand shouted "Wrong!" I asked Hans to try again. Four times in succession he answered 5. At another time Mr. von Osten and I each whispered a number (7 and 1, respectively,) into the horse's ear and asked him to add the two. Three times in succession he tapped 11. After the test had been repeated in accordance with "procedure with knowledge" and a correct response had been received, we tried once more a test of "procedure without knowledge". Again, he responded with an 11. On a third occasion, I asked Hans to tap 5. He responded with a 4 and then, correctly, with a 5. Thereupon, I asked him to tap 6. Again, he responded with a 4. Then I asked him to tap 7. Once more he responded with a 4, and only when I proceeded to count aloud did he tap 7 correctly. I had him repeat the 7 and then went over to 9. Promptly he responded with another 7. In these cases, which by-the-way were not very frequent, we have to do, not with stubbornness on the part of Hans, but with the persistence of that number in the consciousness of the questioner. Modern psychology has recognized this tendency of ideas, which have once been in consciousness, to reappear on other occasions even though they are wholly inappropriate. It has been termed "perseverative tendency." (Perseverationstendenz).[21]

While the errors thus far discussed appeared sporadically in long series of correct responses, there still might be observed at times a massing of errors, usually at the beginning of a day of experimentation or at the beginning of a new series. We were regularly told that Hans always had to have time to adjust himself to new circumstances. The records often showed comments such as these: "After a number of practice tests the horse appears particularly well disposed", or "Hans, at first inattentive, does not respond. Suddenly he gets the hang of things". Different questioners who worked with the horse required different lengths of time to obtain proper responses. Some needed a quarter of an hour, others scarcely half a minute. I, myself, found that in the degree in which I learned to control my attention, in that degree did this phenomenon tend to disappear, but would reappear the moment I became indisposed. From this we see that, instead of attributing all sorts of mental characteristics, such as stubbornness, etc., to the horse, we should lay them to the account of the questioner. As a matter of fact we find that this "getting into the sweep of things", i. e. the overcoming of psycho-physical inertia, has long been known in the case of man and has been experimentally determined and called "Anregung" (excitation) by the psychiatrist, Kraepelin,[22] and his pupil, Amberg.[23] A massing of errors toward the end of a long series occurred only when the questioner was fatigued. There was nothing which had to be interpreted as fatigue or as indisposition on the part of the horse, (except in the few cases of very large numbers, cf. page 67). To be sure, Mr. von Osten always offered these two excuses. That they were without warrant is shown by the fact that Hans, after appearing indisposed or fatigued while working with one questioner, would nevertheless react promptly and correctly a moment later for some other experimenter, and furthermore, when working with me, the number of his correct responses would rise or fall with my own mental disposition.

Finally, I would here note a rather interesting observation for which I am indebted to Mr. Schillings and the Count zu Castell. They had noticed, independently of each other, that the horse would often fail to react when for any length of time he was given problems dealing with abstract numbers, even though they were of the simplest kind; but that he would immediately improve whenever the questions had to do with concrete objects. They believed that Hans found applied mathematics more interesting, and that abstract problems, or those which were altogether too elementary, bored him. The Count zu Castell furthermore noticed that the responses tended to be more correct as soon as he had the horse count objects which he, himself, (Castell) could see during the test. Quite in accord with this is the statement to be found in the report of the September-Commission, in which we find this note in a discussion of the arithmetical problems (not involving visible objects), which the gentlemen already mentioned had given the horse. "The horse responded with less and less attentiveness and appeared to play with the questioner." Here again, that was looked for in the animal which should have been sought in the man. Mr. Schillings was capable of intense, but not continued concentration and it was he who was bored, and not the horse. And it was the Count zu Castell and not the horse that found it necessary to invoke the aid of perceptual objects to bring his attention to the proper height of concentration.

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

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

(c.) When errors in calculation and failures in proper concentration combine, i. e. when the questioner makes a mistake in calculation because he is excited or inattentive and for the same reason does not make the movement, which is the signal for stopping, in accordance with the number which he deems to be the correct answer, then the result is usually wrong, but it may be correct in the few cases in which the two errors exactly compensate each other. Nothing has been so effective in establishing Hans's reputation, nothing has brought him so many followers, as these cases in which he, rather than his mentor, has been in the right. Compared with the mass of cases in which Hans was wrong these latter cases are diminishingly few in number, yet these few made such an impression upon the observers that their number tended to be overestimated. As a matter of fact, I have been able to discover records of only seven such cases. Two of these were reported by the Count zu Castell. On the 8th of September, he entered the horse's stall, alone, and believing it to be the seventh day of the month, he asked Hans the date. The horse responded correctly with 8 taps. At another time he held up before Hans a slate on which were written the numbers 5, 8 and 3 and asked the horse to indicate their sum which in the momentary excitement, vaguely appeared to Castell to be 10. To his chagrin he noticed that Hans continued to tap. Thereupon he intentionally remained motionless until the horse had stopped tapping spontaneously-as he thought-at 16. (The newspapers reported that the numbers to be added had been 5, 3, and 2; that the questioner had expected the answer 11, but that Hans had in three tests always ceased tapping at 10.) In both cases the questioner regarded the answers of the horse as wrong and recognized his mistake when his attention was called to it. I, myself, had the same experience. One time I received in response to the question, "What day of the week is Monday?", the answer 2, although I had expected the answer 1; at another time I asked, "How much is 16 less 9?", and the horse responded with 7 taps, although I had erroneously expected 5. I noticed my mistake only when my attention was called to it by one of those present. Another example is related by Mr. Schillings. A row of colored cloths lay before Hans. Beside them stood an army officer. Pointing to the latter's red coat Mr. Schillings asked the horse to indicate, by means of tapping, the place in the row where a piece of the same color lay. Hans tapped eight times, but Mr. Schillings reprimanded him because the red piece was, as a matter of fact, second in the row. Upon a repetition of the test, Hans again tapped 8. (By some, the facts are recounted as having been the other way round; viz.: Hans tapped 2 instead of 8. This of course would call for a different explanation.) It was noticed that at the place which would be indicated by eight taps there was not a red piece but a carmine colored piece of cloth. A newspaper reports, somewhat vaguely, a sixth case as follows: Hans was asked to spell the name "D?nhoff" and began correctly: "D?". Mr. von Osten, who somehow began to think of another name, "Dohna", interrupted him and wished to correct him by suggesting o instead of ? (i. e., 2 taps instead of 3). Hans, however, continued to spell the entire word with the greatest equanimity. He had not erred. A similar experience is reported by Mr. H. von Tepper-Laski, the well known hippologist. Although the details have slipped from his memory, he reports that in the case in question the correct answer was thrice refused by the questioner who thought that the horse's answer was incorrect. Hans, upon being severely reprimanded in a loud and harsh tone of voice, turned about as if disgusted with the injustice of the man and made straight for his stall.-It is clear that in the cases described we are not dealing with accidentally correct responses, for in nearly every case the test was repeated a number of times and the same responses were received each time. As a matter of fact, my own introspection convinced me that the third and fourth cases were surely, and the first and sixth were very probably, due to insufficient concentration on the part of the questioner. Accordingly there is everywhere in these cases a difference of +1 or +2 between the number thought of and the number tapped (see page 92 f.). The data in the second and fifth and still more in the seventh case were too meager to warrant an attempt at explanation, for it is not even known whether Hans responded with more or fewer taps than was expected by the questioner. It is unfortunate that a more complete record was not made.

The frequent and intentional attempts of Mr. von Osten to induce the horse to give an incorrect response,-which, by-the-way, were regularly unsuccessful-belong only apparently to this group. Thus he asked, e. g., "2 times 2 is 5, is it not?" "3 times 3 is 8?", etc., but Hans refused to be misled, and responded correctly. This was from the very beginning one of the main arguments for independent thinking on the part of the horse. The actual procedure was as follows, even though the questioner had said "2 times 2 is 5", there still was present in his consciousness the number 4. I, myself, would think either of the first member of the equation, i. e., 2 times 2, in which case Hans would respond with 4 taps or I would have in mind the second member, i. e., 5, in which case he would respond with 5 taps. Never did I succeed in thinking of both at the same time. The association between the thought "2 times 2" and the concept "4" is so close and supported by so many other associations that the attempt to form a new one, that is at complete variance with all these, is futile. One may say "2 times 2 equals 5" but it is impossible to conceive it.

Let us turn now, from the tests in counting and computation to those in reading. We have seen that Hans manifested his seeming knowledge of language symbols in a threefold manner: he might approach a slate on which was written the symbol asked for, or he would indicate its location in a series of slates by means of tapping, or finally by means of so-called spelling of the word which was written upon a slate or placard. The responses by means of approaching a placard were very often unsuccessful, while indications by means of tapping were scarcely ever unsuccessful. If it were true that higher intellectual processes[T] were here involved, then the converse would have been expected, for tapping required not only the ability to read, but also the ability to count. If, on the other hand, we assume that the horse simply followed the directions given by the questioner's movements, this seeming difficulty resolves itself, for it would be more difficult for Hans to perceive the signs which he receives while moving than those which he receives while tapping. When we recall that it was easier to direct the horse to a placard near the end of a row than one nearer the center (see page 81), we can readily understand how it was that during the experimentation carried on by the September-Commission (Supplement III; page 255), Hans was able to point out immediately the placards on which were written the names "Castell" and "Stumpf", for they were at the two extreme ends, but was unsuccessful in locating the one on which was written the name "Miessner" which was not a bit more difficult to read, but was located at the fourth place in the row. He first approached the fifth card, then upon repetition of the test he pointed out the other neighboring tablet, viz., the third.

In spelling, Hans was quite indifferent whether his table with the eighty-four number signs upon it stood before him, for he had no knowledge of letters. Neither Mr. von Osten nor Mr. Schillings required it, for the former knew the table by heart and Mr. Schillings told me that before every test he made a note of the numbers which were necessary to indicate the required letters, trusting in this way to control the responses of the horse and never guessing that by so doing he was making it possible for the horse to answer correctly. The newspaper reports aroused much interest at the time by stating that Hans was able to spell such proper names as "Plüskow" and "Bethmann-Hollweg", even to putting in the difficult "w" and "th". The friends of Mr. von Osten at the same time called attention to the exquisite auditory acuteness of the horse which enabled him to perceive the aspirated "w" and to discriminate between the "th" and "t", (the "th" is softer than the "t" in German.-Translator). This explanation, of course, must have appeared somewhat daring even at that time.

Hans was quite guiltless of the many limitations imputed to him concerning his knowledge of symbols. That he was unable to read capitals or Latin script was merely a vagary of the master, like the belief that it was necessary to confine one's self in one's questions to a certain vocabulary and to a certain form. Mr. von Osten's apparent failure to elicit responses from the horse on topics of which it was ignorant is a beautiful illustration of the power of imagination. Mr. von Osten was convinced from the very first that Hans could not answer such questions. When the belief in success was lacking, of course there was not the requisite amount of concentration which, alone, leads to perceptible expressive movements and thus elicits a successful reaction on the part of the horse.

Mr. Schillings, owing to his great impressionability, remained long under the spell of Mr. von Osten's point of view. Thus I find in the record of the September-Commission that the question "How much is 3 plus 2?" was answered incorrectly by Hans, but he responded correctly the moment Mr. Schillings replaced the word "plus" which was "tabooed", by the word "and". For a long time also he could receive no response to questions put in French until one day he made the discovery that, curiously enough, the animal never responded adequately unless he himself firmly believed in the possibility of success. It is noteworthy that the Count zu Castell, independently of Mr. Schillings, made the same discovery. Mr. Schillings made his curious discovery-which he was unable to interpret, but which aroused some suspicion-on the following occasion. One day-whether accidentally or because his prejudice was temporarily overcome-he commanded; "Dis deux!". Hans responded promptly with 2 taps. He was greatly surprised and believed that Hans had gotten hold of the French by hearing it spoken in his environment. Possibly he understood also "trois" and "quatre"? He put the questions and received correct responses. He asked again, "dix", "vingt", and so on to "soixante". At "soixante-six" he became doubtful. Indeed, Hans failed him. At "quatre-vingt", the game began again. "Cent", again, succeeded. The old saying that "Faith will move mountains" was verified once more.[U]

Hans's seeming knowledge of the value of coins and cards, of the calendar and the time of day, as well as his ability to recognize persons or their photographs, can now be readily understood. In all of these cases, we had to deal, in so far as knowledge is concerned, only with that of the questioner,-the horse simply tapped the number the questioner had in mind. The meaning which was supposed to be expressed by the tapping never existed as far as Hans was concerned; it was only in the mind of the questioner that the concepts: ace, gold, Sunday, January, were associated with "1", etc. The same was true with regard to all other wonderful feats of memory. The sentence: "Brücke und Weg sind vom Feinde besetzt", (The road and the bridge are held by the enemy), which was given to the horse one day and correctly repeated by him on the following day, was not an answer elicited from the horse by means of a question, but rather a system of automatic reactions which were induced by certain involuntary movements of the questioner as stimuli. Far from showing a wonderful memory in these feats-as is claimed for him by the very non-critical compiler, Zell[28]-Hans, on the contrary, has at his service a remarkably small number of associations. For, besides possessing the powers of any ordinary horse, he recognizes only a few meager visual signs. To be sure, we find in the literature a horse that was said to have recognized 1500 signals,[29] but all proof is lacking and the report is so meager that we cannot discover whether these signs were auditory or visual.[V]

Having thus disposed of all questions concerning the horse's apparent feats of reason and memory, let us turn to those in the field of sensation. We shall begin with vision. That Hans was unable to select colored pieces of cloth merely upon the basis of color quality, without reference to their order, was shown in Chapter II. It would, however, be somewhat hasty to infer color-blindness from this fact, as did Romanes[32] on the basis of similar unsucessful responses on the part of a chimpanzee ("Sally" of the London Zo?logical Garden). It is much easier to explain the failure of the horse than that of the monkey on the basis of intellectual poverty, a poverty of associative activity. It presumably can discriminate between the various colors, but it cannot associate with these their names. The existence of chromatic vision in the lower forms is by no means as unquestionable as is assumed by popular thought. Even teleological considerations which are often brought forward (especially that of the ornamental and protective coloring of so many animals) can never do more than establish a certain probability. For definite proof, we need data given by observation (we have none in this case), or experimental evidence. Such evidence we have, but it is insufficient in quantity and unfortunately most of it was obtained under inadequate experimental conditions.[W] We know nothing regarding chromatic vision in the horse, though we have often had trained horses which apparently possessed color discrimination. The earliest report of this kind I find in a work published in the year 1573.[36] Here we read that a number of Germans exhibited two horses in Rome which could, upon request of their masters, point out those persons among the spectators who were wearing stockings of any designated color. The passage, "conoscevano i colori", (they recognized the colors,) proves nothing and no one has ever heard, even in modern times, of a horse that actually knew colors.

Nor did Hans possess anything like that high degree of visual acuity which had been attributed to him. He was supposed to be able to read easily at a distance small, almost illegible script, which we ourselves could decipher only with the greatest difficulty close at hand. It was also supposed that he could distinguish ten-and fifty-pfennig pieces whose faces had become worn beyond recognition for us. None of these accomplishments have stood the test. We have no reason to believe that Hans can see the objects about him more clearly than other horses, regarding whom one usually assumes that they receive only vague visual impressions. Horses do not as a rule seem to be near-sighted as is often asserted by the layman, but rather somewhat far-sighted, or if we may believe Riegel,[37] who tested some six hundred horses, they probably have normal vision. But we are told that many horses-and according to some authors all-have an innate imperfection which detracts considerably from the clarity of vision. This imperfection consists in an irregular formation of the sclerotic coat and of the lens of the eye.[38] The two organs do not have the same refraction in all parts. As a result, objective points are not imaged as points upon the retina. (Hence the name: astigmatism, i. e., "without points", for this disorder.) The retinal image of the object is not only vague, but also distorted.[X]

Many will doubt whether with such imperfect images an animal can react to directives so minute, as we have asserted to be true in the case of Hans. In considering this question we must distinguish between the directives for pointing out colors and the directives for tapping and for head movements on the part of the horse. In pointing out and bringing forth pieces of colored cloth there is involved the perception of an object at rest, viz.: the direction of the questioner who is standing quietly; whereas in the case of responses by means of tapping the stimulus is the horse's perception of the questioner's movements. Now, the construction of the horse's eye, as described above, is not favorable for the perception of objects (so-called acuity of vision). This may partly account for the slight success of the horse in those tests in which he was required to select a piece of cloth of a designated color, in so far as these commands were not accompanied by calls or exhortations. Where human observers averaged eighty per cent correct responses (page 135), Hans, under similar conditions was successful in only one-third of the tests. In his errors he was also wider of the mark than were the human observers (page 82). The object perceived, to be sure, is a large one, viz.: the questioner, and he at close range. We must therefore consider more specifically what are the determining factors that make for success or failure of the response. First of all, the innocent questioner very often did not designate the direction with sufficient clearness. Furthermore, Hans presumably was not able to discriminate sufficiently between the direction of the experimenter's eye and that of his head, which two directions did not always coincide. Finally the horse's attention was often diverted, while he was running toward the piece indicated, by the other pieces lying to the right and to the left, and for this reason the addition of a single piece to the otherwise unchanged row of five pieces tended to decrease greatly the chances of success.

The case is different with the perception of the directive signs for tapping, for nodding and shaking the head, etc., all of which require the perception of movements. This is not necessarily more difficult on account of the imperfect constitution of the tissues that serve for the refraction of light. Some authors even aver that this facilitates the perception of moving objects. This view was first advanced by the excellent ophthalmologist, R. Berlin[39] of Stuttgart. In arriving at this view he was guided by the following considerations. The peculiar form of astigmatism of the lens of the horse's eye, which Berlin has described as "butzenscheibenf?rmig",[Y] because it appears in the form of a series of glossy concentric circles around the lens nucleus, has the property of enlarging the pathway (and with it the rapidity) of moving retinal images. If we take a speculum by means of which a view may be had of the interior of the eye, and fixate a definite point on the retina of the horse, and then make a slight movement of the head horizontally, we find that the point fixated moves-apparently at least-toward the border of the pupil. In a normally constructed eye this seeming movement will be in a straight line, while in the eye of the horse, (according to Berlin), its path is curved, and therefore longer. Berlin believes that the same thing which here occurs in the case of this merely apparent movement, must also happen when an external moving object is imaged on the horse's retina. Its pathway, too, will be curved, and therefore longer, so that if the head of Mr. von Osten moves past the animal's eye, then the image on the horse's retina will take a longer, more circuitous route than it would if the eye were not astigmatic. We cannot, however, immediately conclude from the fact that an objective movement is imaged as being greater in extent on the retina, that it will therefore be more readily perceived by much less that it will appear greater to, the horse, than would be the case if the lens were normally constructed. The visual percept is not immediately dependent upon the retinal processes, for between the two are interpolated complex, inaccessible nervous processes. Still, Berlin believes that he is justified in drawing this conclusion from a number of relevant considerations. Accepting it, he believes that it would be possible for the horse to perceive movements, that for the human eye, which is not subject to this form of astigmatism, would lie below the threshold.

This theory, the simplicity of which certainly must make a strong appeal, has been adopted by a number of well-known investigators (Schleich[40], K?nigsh?fer[41]). If we also could accept it, then Hans's phenomenal power of perceiving the movements of objects would be explained. But doubts arise which restrain us. Even if we were to accept Berlin's view in general, we should still come upon the following difficulties. In the first place, it is questionable whether the peculiar form of astigmatism mentioned is indeed as common as he supposes.[Z] The references in the literature are exceedingly meager on this point. In order to make a few tests at least, I undertook to examine nine horses with the aid of Dr. R. Simon, oculist, to whom I am greatly beholden for the assistance given in these and other tests to be mentioned presently. In not one of the nine cases did we discover anything like the curved deflection which is supposed to be the sign of the form of astigmatism in question. But in order to test objectively whether Berlin's assumption were justified, we examined in the laboratory fresh specimens taken from two horses. The eyes were fastened in a frame in what corresponded to their normal position. Their posterior spherical wall (i. e., their respective retinal surface) was replaced by a piece of ground glass. On a spherical surface linear movements of a point of light are always imaged as curves, no matter what the shape of the lens forming the image may be. (For a more detailed statement see page 170, at close of note.) Since, however, our investigation had to do only with those curves which were due to the qualities peculiar to the lens, we had to replace the spherical by a plane projection surface. In front of the eye thus modified a strong light was placed at such a distance that the image of it, produced on the improvised back of the eye by the cornea and the lens, was a sharply defined point of light. Now, when the source of light was moved, the point of light would also move on the glass plate. Sitting at some distance behind the eye, we observed the movements of this point through a telescope. Thus we became witnesses of what happens upon the horse's retina when a moving object passes in front of his eye. Although we saw the point of light move through relatively long distances both horizontally and vertically, no sort of deflection in its pathway could be noted. Berlin's exposition does not hold true for the eyes of the horses, either living or dead, which were examined by us.

But in the case of some of the horses in whom Berlin had seen the phenomenon for which we sought in vain, he himself tells us, the deflection was very slight. In that case, it would appear, no great advantage would be gained along the lines indicated. But even assuming the degree of deflection to be very great, his theory goes to pieces on the very point it was supposed to explain. A concrete example will make this clear. If Mr. von Osten, standing two feet away from the horse, raised his head 1/5 millimeter (which figure by no means represents the extreme values that were obtained), then in the horse's retinal image every point of the man's head would move through a distance of 0.0025 millimeter-assuming the horse's eye to be free from astigmatism and assuming its focal distance to be 25.5 millimeters. If, however, other conditions remaining the same, we presuppose an extreme form of astigmatism, one in which the path of the retinal image is not a straight line, but is deflected into a semicircle, then each point would pass through a distance of nearly 0.004 millimeter. If the sensitive retinal elements have a diameter of 0.002 millimeter (as Berlin, somewhat inexactly, states), then from two to four elements would be stimulated in case there were no astigmatic deflection. But in case the deflection did take place, it would not necessarily involve more elements, as can be seen by making a simple graph; indeed we can imagine cases in which the circuitous path would involve even fewer elements than the straight one. And finally, when the movement which the horse is to perceive, does not occur in a straight line but in the form of a curve, (which will generally be the rule), then the astigmatism will tend in many cases to decrease the curvature of the image's path on the retina, and sometimes even obviate it entirely. In all these cases, on Berlin's own theory, the perception of the movements would be hindered rather than aided.[AA]

But to come now to the most pertinent objection. We saw that Berlin's whole train of thought rested upon the assertion that it made no difference whether we regarded by means of the speculum the seeming movement of a fixed retinal point, or whether the image of an external moving object is passing over the horse's retina. As a matter of fact, however, these two processes are very different from one another. In moving the mirror, with its small opening we are looking through ever changing portions of the horse's lens,-testing it out, as it were. The horse, on the other hand, sees with all parts of the lens simultaneously, in so far as the lens is not covered by the iris. The arcuate deflection, which is nothing but a registration of the difference in the indices of refraction of the different parts of the lens used consecutively, might thus be formed for the observer using the mirror, but never for the horse. For these reasons we cannot conclude that the kind of astigmatism described can really increase the horse's acuity in the perception of movements.

Since the light-refracting apparatus of the horse's eye does not offer a satisfactory explanation for the extraordinary keenness of visual perception possessed by the Osten horse, we must go a step further and ask whether it may not perhaps be found in the part immediately sensitive to light, the retina. That portion really would seem to be adapted to the perception of movements of minimal extent, and for this reason: it is more than three times as great in extent as the human retina, and the horse's retinal images are likewise larger owing to the position of the nodal point. The cells of the retina that are sensitive to light, the rods and cones, might therefore be correspondingly larger than those of the human eye, without thereby making the whole organ less efficient than the human eye. But the most recent measurements[51] have shown that the rods and cones of the horse's eye are more minute than ours. Assuming that, in the case of the horse, as is presumably the case in human vision, the transition of a stimulus from one retinal cell to the next already in itself induces a sensation of movement, then the horse ought indeed be extraordinarily keen in the perception of moving objects (provided that the horse's more minute cells are packed just as closely as in the human retina). And besides, there are two specially adapted areas within the retina of the horse. The "band" ("streifenf?rmige Area") which was discovered fifteen years ago by Chievitz,[52] is a strip of 1 to 1? millimeters in width, traversing the entire retina horizontally, and is noteworthy on account of its structure and probably, too, on account of its greater efficiency. It may have something to do with the accomplishments of the Osten horse; but in how far it would be hard to say. The other noteworthy portion of the horse's retina is the "round area" discovered some four years ago, located at the rear outer end of the "band", and it is the best-equipped part of the horse's retina and corresponds to the area of clearest vision, the yellow spot, in the human eye. But this round area need not come in for consideration by us, for its location would indicate that it is used in binocular vision, that is, seeing with both eyes.[53] But in all our experiments the Osten horse observed only with one eye. That does not mean, however, that under other circumstances the round area may not be of very great importance.

In the present state of our knowledge, all attempts at explanation are, of course, of the nature of hypotheses. If further investigations should disclose this explanation to be untenable, then we would either have to suppose some unknown power in the eye of the horse,[AB] or else seek a cause in the animal's brain. Further experiments on other horses would be necessary in order to discover whether the species as a whole possesses this ability or whether only certain ones are thus endowed. The former is of course more probable. In this particular case conditions were unusually favorable for the development of this ability. We must bear in mind that in all probability Mr. von Osten's movements very gradually became as minute as they are now, and that therefore Hans at first learned to react to such as were relatively coarse. Furthermore, his practice extended throughout four years and during this time it was his sole occupation. Without specific predisposition, however, all this practice would have been utterly futile. We can also readily appreciate how indispensable in the struggle for existence a well-developed power of perceiving moving objects must be to horses (and most other animals) living in their natural condition and habitat, in order to be aware of the approach of enemies, or, in the case of carnivora, the presence of prey. In view of all these considerations we can readily see how it was possible that the horse, perhaps in spite of rather defective vision, could react with precision to movement-stimuli which escaped observation by human eyes.

We can understand also the horse's never-flagging attentiveness when we recall that self-preservation prompts eternal vigilance over against all that is going on in the animal's environment. (In the case of Hans, hunger was at first the motive; later, habit did the work.) Furthermore, the lower form is not hindered in giving itself over to its sense-impressions by the play of abstract thought which tends so strongly to direct inward our psychic energy,-at least, in the case of the cultured.

Nevertheless, Hans still remains a phenomenon not only in excelling all his critics in the power of observation, but also in that he is the first of his species, in fact the first animal, in which this extraordinary perceptual power has been proven experimentally to be present. It has long been known[55] that horses could be trained to respond to cues in the form of slight movements, which remained unnoticed by the layman, and this fact has been made use of by circus trainers to its fullest extent. But such signs, I have discovered, are without exception, of a far coarser sort than those we have here described, and they can be instantly detected by the practised observer. Nor was it known to professional trainers that it was possible for the master to direct a horse to any point of the compass simply by means of the quiet posture of the body. For this reason it was believed that no signs could possibly be involved in the color-selecting-tests (cf. Supplement III, page 255). In this we have the support of some of our experts, as is witnessed by the following extract from a letter of his Excellency Count G. Lehndorff, one of our best hippological authorities, who at one time carefully examined the Osten horse. (The letter was addressed to Mr. Schillings, and I have permission of both gentlemen to use it). In it he says: "If the author's statements, in which you also have concurred, are correct, and if, as a matter of fact, the horse really does react to such minute movements as are absolutely imperceptible to the human observer, then we have indeed something quite new, for hitherto no one would have believed that horses can perceive movements which man cannot. But I am even more surprised by the explanation of the color-selecting feats.-This too, is something absolutely new. One would not have deemed it possible that a horse could do anything of the kind simply by using the posture of a man's body as a cue to which it could react with such precision."

And yet, even though both facts were new concerning the horse and had not hitherto been proven experimentally regarding any other species, nevertheless something of this sort has been known concerning the dog for some time. His ability to single out an object upon which his master had intently fixed his gaze, was made the basis of a special form of training, called "eye-training,"[56] nearly one hundred years ago. The dog was taught to focus constantly upon his master's eyes and then upon command to select the object which he, the master, had been fixating. Such a dog has been described by the naturalists A. and K. Müller.[57] But the master of the dog, unlike Mr. von Osten, would not permit anyone else to work with the animal, and the two brothers, recognizing the trick, were justified in adding that "the whole affair aimed at deceiving the public, and the dog's reputation was but a means of making money". The success of such exhibitions appeared furthermore, to depend upon the close proximity of the trainer and the dog, whereas the direction of the head (and even of the body) could very probably be perceived at greater distances also. At least we learn from a reputable source that in the hunt, dogs can perceive from the mere posture of their master, what direction he intends to take.[58]

But a still more curious fact is this, that dogs, too, learn-evidently spontaneously-to react to the minimal involuntary expressive movements of their master. The first example mentioned in the literature on the subject is that of an English bull-dog called Kepler, belonging to the English astrophysicist, Sir William Huggins.[59] We are told that this dog seemingly could solve the most difficult problems, such as extracting square roots and the like. The numbers were indicated by barking,-thus one bark was for one, two barks for two, etc. Every correct solution was rewarded with a piece of cake. Huggins states explicitly that he gave no signals voluntarily, but that he was convinced that the dog could see from the questioner's face, when he must cease barking, for he would never for an instant divert his gaze during the process. Huggins was unable, however, to discover the nature of the effective signs. This satisfactory, though still unproven, explanation has been accepted by specialists, among them Sir John Lubbock.[60] I, too, regard this dog as a predecessor of our Hans.

A similar case is reported by Mr. Hugo Kretschmer, a writer of Breslau, in the "Schlesische Zeitung" of August 21, 1904. To him I am beholden for a detailed written statement, which he has kindly permitted me to use in this connection. The gentleman named, first trained his dog to ring the table-bell, and this, by pressing the dog's paw upon the bell-button. When the dog had learned to do this independently, his master tried to teach him the rudiments of numbers, in such a way that the animal was to give one ring of the bell for the number 1, two for 2, etc. But these attempts failed utterly and had to be abandoned. But Mr. Kretschmer had noticed that he was able to get the dog to ring any number which he, Mr. Kretchmer, might decide upon. (Success was always rewarded by a bit of bread and butter.) At first Mr. Kretschmer tried to imagine vividly only the final number, but failed thereby to elicit correct responses from the dog. But he did succeed when he tried making a series of separate volitions. Thus for the number 5, he would "will" each separate push of the button on the part of the dog. Even so, however, he never got beyond 9, for then the dog would become impatient and would ring the bell continuously. Anything that diverted the dog's attention, such as noises, etc., also entailed failure. In these tests master and dog had faced each other, each gazing steadfastly at the other. Mr. Kretchmer was convinced, however, that the dog was not guided by any sort of sign, but rather by suggestion. He based his belief on the following two observations. After some practice, he says, the tests were also successful when he did not look at the dog, but stood back to back with it, or when he screened himself from the dog's view by stepping to one side behind a curtain. The tests were unsuccessful, on the other hand, whenever he was mentally fatigued or had taken some alcoholic drink. The arguments do not appear to me to be adequate. If he turned his back upon the dog and no other observer was present, he had no means of knowing whether the dog did not, after all, peer around to get a peep at him. If others who knew the desired number, were present, the dog might have gotten his cues from them. And there may be some doubt whether the curtain adequately served the purpose for which it was intended. At any rate, it was added that all attempts to influence the dog from an adjoining room-which would thus exclude effectively all visual signs-were utter failures. I am also strengthened rather than weakened in my belief, by the second argument which Mr. Kretschmer makes, viz.: that mental fatigue or the use of alcohol on the part of the questioner tends to make the result unsatisfactory. We noted a similar effect in the case of the horse (page 150), where a disturbance of the "rapport" between the questioner and the horse was invoked by some by way of explanation. The facts were explained by us much more simply. We attributed the result to the close correlation between the type of mental concentration and the nature of the expressive movements-a correlation which we have shown experimentally to exist. I cannot, therefore, subscribe to the view that this dog did not require either visual or other sensory signs. The tests which were made for the purpose of strengthening that view, are on a par, I believe, with those mentioned on page 45. And since auditory, olfactory, and other stimuli, though not impossible, still are improbable, I believe that our Hans, Huggins's dog, and the one belonging to Mr. Kretschmer, differ from one another only in this, that the first taps, the second barks, and the third presses a bell-button.

And finally I have access to a letter from the Rhine Province in which there is a brief account of a dog that would promptly obey any command that was given without a sound and supposedly without the accompaniment of the slightest kind of gesture. It is specially mentioned that the animal steadily watched its master during these tests. The perception of the slightest involuntary expressive movements is in all probability the secret in this case also. Here, too, suggestion has been invoked by way of explanation, but there was not the slightest attempt made to find for it a more specific foundation, and we cannot suppress an objection based on the matter of principle. It is incumbent upon anyone who uses a term so ambiguous, to define what content he desires to have put into it. If he does not do this, he is giving us, instead of a concept, a bare word, instead of bread, a stone.

While we must reject the explanation based on suggestion,[AC] we believe, on the other hand, that we have here again, evidence of the presence of visual signs, given unwittingly and involuntarily, just as I am sure that they were involved in the two preceding cases, and similarly in the case of the Huggins dog. Since the effective signs were discoverable in none of these canine predecessors of Hans, an investigation would be desirable, based upon the insight gained as a result of these experiments upon Mr. von Osten's horse. Unfortunately this is impossible, since the dogs in question are dead. But others like them undoubtedly exist in many places. We might mention that when Hans first came under the limelight of public attention, there was also frequent reference to the Huggins dog, but he soon dropped out of the discussion again.[63] And this for two reasons. The dog never took his gaze from his master and appeared to be entirely dependent upon him in his reactions. Hans, on the other hand, seemed to give evidence of a high degree of independence and never appeared to look at the questioner. But we know now that, though he was never dependent upon the will of his master, he, too, abjectly hung upon the man's involuntary movements and never for a moment lost him from view. But since the horse is able to observe with one eye alone, and needed to direct only it and not the entire head toward the questioner, in order to focus comfortably, one could not conclude as to his line of vision from the direction of the head. Since, furthermore, in the horse the pupil is hardly distinguishable from the darkly pigmented iris and since the white sclerotic is hidden by the eyelids, except when the eye is turned very much, it is difficult to determine what direction the eye is taking. I once purposely stepped backward to the horse's flank, so that he had to turn his eye far back and thus the outer border of the iris and the white sclerotic coat became visible and all doubt concerning the line of vision was removed. This doubt could never arise in the case of the dog, the median plane of whose head is always directed toward the object fixated, and Zborzill is justified in saying, as he does, in his discussion of training of the kind mentioned on page 177, "But any careful observer can immediately guess the manner in which such a dog has been trained."[64] If Hans had chanced to possess so-called "glass-eyes"-in which the dark pigment is wholly or partly lacking, so that the black pupil is clearly defined against the lighter background,-then no doubt could ever have arisen concerning the direction of the eye, and Hans never would have come to be regarded as the "clever" Hans.

After the publication of the December report, Hans acquired a reputation for excellence in thought-reading and thus the discussion of thought-reading among animals in general became once more the order of the day. That is to say that many of our domestic animals are-like the human mind-reader (à la Cumberland),-supposed to have the ability to infer the thoughts of their masters from slight, involuntary movements. They are thus aware when the feeding hour approaches, when they may go out in the open, etc. They also appear to be aware that their welfare lies in our hands, and therefore would seem to have a vital interest in divining our intentions and our wishes. Not only our spoken words, but also numberless movements-usually without our knowing it and often contrary to our desire-speak a clear language. As is well said by the American neuropathologist, Beard,[65] (who first explained the phenomenon of thought-reading, on the basis of the perception of very minute muscular jerks, and therefore called it "muscle-reading" or "body-reading"): "Every horse that is good for anything is a muscle-reader; he reads the mind of his driver through the pressure on the bit,-though not a word of command is uttered." We know that in the case of perfectly trained horses the rider's mere thought of the movement which he expects the horse to make, is seemingly sufficient to cause the animal to execute it.[AD] Such cases are of course very much like that of our Hans, excepting that instead of visual signs they involve aids of a mechanical nature, which, however, does not alter the general principle, since both of them are of the nature of sensory stimulation. But we must not overlook the essential difference between this so-called thought-reading on the part of animals and that which is done by man. The human thought-reader can interpret movements, for he is familiar with the ideas which are their source. Thus when at the second tap, I notice a very slight jerk of the subject's head, and a stronger one at the fifth tap, I infer that he thought of the problem 2+3=5. While the experimenter thus cannot be said to read thoughts, he still infers them. The animal, on the other hand, we may be reasonably sure, draws no such inferences. In its conscious life it remains ever on the sensory level. If we could ask Hans about it, he would probably answer: "As soon as my master stoops forward, I begin to tap; as soon as he moves, I stop. The thing which induces me to act thus is the carrot which is given me; what it is that induces my master to make his movements, I do not know."-It is therefore erroneous to believe that animals require the power of abstract thinking in order to utilize the signs which are consciously or unconsciously given them, as is argued by Goldbeck[68] when he says with reference to the training for visual signs, which we have already mentioned before: "There the dog has consciously interpreted the visual impression in terms of the conclusion that he is expected to bring forth the leaf indicated." Nor was there any justification for the critic who thought he could put the essence of the report of December, given in Supplement IV, into the following words: "He (Hans) showed that he has the power of attention, can draw logical conclusions, and can communicate the result of his thinking,-and all this independently." Yet none of this had been asserted. The whole thing may be explained satisfactorily by means of a process of simple association established between the signs observed in the master and certain reactions on the part of the horse. The fact that the movements made were so exquisitely minute does not change the matter in the least. Such signs call for a high degree of sensory keenness and great concentration of attention, but by no means an "extremely high intelligence."

Let us turn now from the consideration of visual perception to that of auditory perception in the horse. We saw that the fact that Hans was able to respond to commands which were only inwardly enunciated, that is, commands which were merely thought of but not spoken, was not proof of great acuity of hearing, but rather that hearing was not at all involved. If Hans had been deaf he would, none the less, have promptly obeyed the commands. Blind and near-sighted horses try to overcome their deficiency by means of the sense of hearing, and hence show a pronounced play of ears. In the case of the Osten horse, however, attention has been diverted from auditory stimuli in the process of habituation to visual signs, and as a result ear-movements are almost completely wanting. One is not of course permitted to deny a priori that perhaps some associations might have been formed between objects and the vocal signs belonging to them, e. g., between the colored cloths and the names of the colors if both had been presented together oftener than was the case.

But there is a dearth of reliable observation as to how far auditory associations of this sort may be established in horses. Usually the following is cited. Horses learn to start off, to stop, and to turn about in response to calls. They are able to distinguish properly between the expressions "right" and "left", or equivalent terms. Upon command they will start to walk, to trot or to run. And they also know the name by which they are usually called. All authors agree that cavalry horses understand the common military commands; one writer even avers that they excel the recruits in this respect.[69] Some believe that in riding schools the horses pay closer heed to the calls of the riding-master than to the control of unpractised riders, even when the two are at variance with one another.[70] My experience with the Osten horse and a number of other pertinent observations aroused in me the suspicion that much that is called or spoken in the process of managing a horse may possibly be just so much labor lost. In consequence I made a series of relevant experiments. I have thus far tested twenty-five horses of different kinds, from the imported Arabian and English full-blood, down to the heavy draft-horse. The experiments were made partly in the courtyard of military barracks, partly in the circus, and partly in a riding-school or in private stalls. I am specially indebted for kind assistance to Messrs. von Lucanus, Busch, and to H. H. Burkhardt-Foottit and E. Schumann, the two excellent trainers connected with the Busch Circus. During these tests, the horses were always amid circumstances familiar to them, whether free or bridled, under a rider or hitched to a wagon. All aids or signals, except the calls, were eliminated in so far as it was possible.

The results of those tests were in substance as follows: Many horses react to a smack of the lips by a rather fast trot. Many stop on the cry "Hola" or "Brr". This last was nicely illustrated in the case of two carriage horses supplied with large blinders and held with a loose rein, and hitched to a landau. One of them regularly stopped when the "brr" was given by the driver, whereas the other, which had not been habituated to this signal, kept serenely on the trot, so that the vehicle regularly veered off the track-a sure sign that no unintentional aid was being given by means of the reins. Other horses, again, were accustomed to halt in response to a long-drawn-out "hola", but it was the cadence of melody rather than the word that was effective, since any other word, or even a series of inarticulate sounds, would produce the same result, provided they were given with the proper inflection. When this was changed, then the response would fail.

The result was not so apparent when it came to controlling the kinds of gait. One riding-school horse, when lunged and in a gallop, could be induced by a friendly call-the word again was a matter of inconsequence-to slacken his pace into a trot and from a trot into a walk. But this reaction was by no means very precise. Another, a full-blood, contrary to the trainer's expectation and to his great astonishment, failed to respond to any kind of spoken command as soon as the one who carried the reins refrained from making any movements which might indicate what was wanted. (To refrain from all expressive movements of this kind is by no means an easy matter). The slightest move, apart from any help by means of the reins or the whip-handle, was sufficient to evoke a response. The results in the case of the military horses, differed in many particulars. Thanks to the courtesy of Captain von Lucanus I had the opportunity of testing three cavalry horses, two geldings and one mare, aged nine, thirteen, and nineteen years respectively, and all of them in the regiment ever since their fourth year. They had been selected as the "most intelligent" in the squadron, and we were assured that they would obey punctiliously all the usual commands. They were ranged behind one another, with the customary distance of two horses' lengths between, and were ridden each by his accustomed rider. Both starting and stopping upon command were tested. The horses were held by the reins, but the riders were cautioned to refrain from giving any aid that might cause the horse to start when starting was to be tested, or that might restrain him when stopping in response to the spoken command was to be tested. If a suspicion arose-a thing which happened only twice, however-that a rider had actively aided in his horse's reaction, then an officer would mount into the saddle. If it appeared that one of the horses was simply imitating the others, then the others were purposely restrained by their respective riders. The commands were given by the corporal who usually had charge of the horses. In a few cases the sergeant of the squadron gave the commands, but this made no difference in the success of the experiment. Now as to the results. Whenever the horses were trotting or walking, all commands, without exception, were in vain. They effected neither an increase nor a decrease in the pace. A result was obtained only when the horses were standing when the test began; and this result was simple enough,-upon certain calls the animals would respond by beginning to walk. This was the only reaction that was obtained. The most effective of the commands appeared to be "Squadron,-march!" But the command "Squadron!" or "March!" alone, were quite as effective; yet none of these commands was obeyed without exception. Reactions were occasionally obtained in response to "trot!", "gallop!" "retreat!", (the usual introductory "squadron" was purposely omitted here, because it alone sufficed to start the horses). But the reactions were always the same, viz., to start on a walk. Another series of commands (such as those which are addressed to the rider alone, e. g., "Lances down!") had no effect whatever; a certain amount of selection therefore did seem to take place. In all these tests the order of the horses with reference to each other's position was repeatedly changed. One of the horses, the youngest, and reputed to be the most "intelligent", (he was as a matter of fact the most spirited), gave evidence of a gregarious instinct, intensified by habit, which, if it had been overlooked, might have become a source of serious error. Not being accustomed to go at the head, when so placed it started properly in only 18% of all such cases. When, however, (other conditions remaining the same,) he was put in second or third place, he started properly in 67% of the tests, and if we take into account only those cases in which the three most effective commands were used ("Squadron!", "March!", and "Squadron-march!") he reacted correctly in 91% of the cases. (The number of tests was 17, 36 and 22 respectively for the three groups mentioned.) The horse, therefore, almost always began to step properly when he stood behind one of his companions, but seldom when he stood at the head. And when he stood at the head and began to walk at the proper moment, it was plain that it was a case of imitation and not initiative, for the horse was still able to see the others, owing to the extent of his field of vision backward, and he was always the last to move, whereas otherwise he was always the first to move, and always difficult to restrain. So when the horses to the rear were restrained or when the intervening distance of two horses' lengths was lessened, so that this gelding could not see the one in the rear, he failed completely to respond. Accordingly these three horses did little to justify the faith which their squadron had placed in them.

Now a few words on the manner in which horses react upon the call of their names. We are not concerned with those that are seldom or never called by name (such as those in the cavalry). I have not discovered one horse that constantly and unequivocally reacted upon the mention of its name (though I would not assert that there are none that would do so.) I was nearly always able to convince the owners or grooms, who at first had maintained a contrary opinion, that any inarticulate sound was capable of producing the same effect as the calling of the name. What the significance of inflection may be, I am not at all certain. When a certain one of a number of horses standing in the same stable was called, all of them responded by pricking their ears, raising their heads, or else turning about. For this reason the reaction of the horse specifically called lost all significance. Likewise the call which is ordinarily used in lunging when the man in the center of the circle wishes the horse to change its gait, or to advance toward him, also proved ineffectual as soon as the man inhibited every sort of movement. A slight nod, on the other hand, was always effective. Several times I have tried to call horses to me, when they were free and running about in the arena, but was unsuccessful. After I had given them some sugar, however, they would always come to me-whether I had called or not-and would then refuse to leave my side. But this is a matter of common observation.

I would, however, regard all of these tests as merely provisional. In spite of the greatest effort, it was not always possible to control all the conditions of the experiment, and furthermore, the number of tests would have to be materially increased in order to yield an appreciation of the difference due to race, age, and the individual variation and training of horses. But we may, even now, be sure of one thing. Over against the certainty with which horses react to visual stimuli (in the form of movements perceived), it does not appear that the formation of auditory associations is greatly favored by nature in these animals,-indeed, auditory associations are far less common than is generally supposed.[AE] Horses compare very unfavorably with dogs in this respect. The latter easily learn to react with a high degree of precision to auditory signs,-as I learned from a series of experiments which I was enabled to perform. The Osten horse, therefore, does not stand alone among his kind in his inferior auditory equipment, as one might be tempted to believe at first blush.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

FOOTNOTES:

[T] Professor Shaler[24], a well-known American savant, mentions a three-year old pig belonging to a Virginian farmer, that was able to read and had some understanding of language. From numerals which were written upon cards and spread out before it, this pig could compose dates. It could also select from among certain cards one upon which was written a given name, asked for by the master. Supposedly no signs of any kind were given. (Shaler thought to exclude effectively the sense of smell, which is so highly developed in the pig, in that he, Shaler, himself smelled at the cards, since he also "possessed an acute olfactory sense!") Since we are told that the farmer in question made a business of supplying trained pigs for exhibition purposes, the case appears suspicious. We hear of a pig exhibited in London, that was able to read and spell, and could also tell the time by the watch[25]. We cannot tell, however, whether the two pigs, which beyond a doubt were mechanically trained to respond to signals, are identical or not.

[U] It has been scientifically proven that a number of supposed mystical phenomena, table-moving, table-rapping, and divination by means of the rod, all are the result of involuntary movements made unawares by those concerned, just as in the case of this work with Hans. (We must of course except those not infrequent instances in which the phenomena in question are purposely and fraudulently simulated.) There is this difference, however, that there the thing affected is a lifeless object,-the table or the rod,-here it is a living organism, the horse; hence there the immediate effect of the movement is physical work in the form of energy expended in moving the table, here the movement becomes a visual stimulus. A number of observations which I find in the relevant literature, and which I shall introduce into this chapter, may serve to show how close is the similarity between the two cases, how much depends upon the questioner, and how little really upon the instrument-whether table or horse-which is acted upon.

Two examples will suffice to illustrate the significance of belief and of the concentrated attention that results from it. The first is taken from the letters of Father P. Lebrun on the divining rod[26], which appeared in 1696. An old woman once told a treasure-seeker that she had always heard that a treasure was buried at a certain place in the fields. The man, who was known as an expert in the art of using the divining rod, immediately set out to locate the gold. Lo, and behold, the moment he set foot on the spot described by the old woman, the branch turns downward, and from its movements the man gathers that twelve feet below ground there lies buried some copper, silver and gold. He calls a peasant to dig a pit eleven feet deep, then he sends him away so that no other should get into the secret. He himself digs a foot deeper, but all in vain, for he finds nothing. Standing in the pit, he again takes up the branch. Again it moves, but this time it points upward, as if to indicate that the treasure had disappeared from the earth. Dismayed, he climbs out of the pit and questions the branch a third time. This time it points downward once more. He climbs back into the pit. Presently he feels the prick of conscience (for in the 17th century many regarded the dipping of the divining rod as the work of the Devil). Terrified, he exclaims: "O God, if the thing I am doing here is wrong, then I renounce the Evil One and his rod (s'il y a du mal, je renonce au démon et à la baguette)". Having spoken, he once more takes the rod in hand to test it. It does not move. Horrified, for now there was no longer any doubt that Satan was the cause of its movements, the man makes the sign of the cross and runs away. But he had hardly gone more than two or three hundred paces when the thought strikes him: Is it really true that the branch will no longer move for him? He throws a coin to the ground, cuts a branch from a bush nearby, and is overjoyed when he notes how it dips down toward the money.

Another example is to be found in a report of the well-known physicist, Ritter[27], of Munich, which appeared during the early part of the 19th century. Ritter, a man with a bent for natural philosophy and metaphysics, describes an instrument which was to replace the divining rod, and which he called "balancier." It was simple enough, consisting of a metal strip that was balanced horizontally upon a pivot, and was supposed to be put into motion in the presence of metals. Ritter used this instrument in his numerous experiments with the Italian Campetti, a man who had achieved a measure of fame in Europe for his ability to discover springs and metals by the use of the divining rod. Carrying the "balancier" on the tip of the middle finger of his left hand, Campetti-whose integrity one cannot cavil at-had to touch repeatedly a plate of zinc or pewter, and had to count aloud the number of touches he made. The following curious law was found to obtain (that was probably suggested to the subject by Ritter without his being aware of it): with the first contact the "balancier" turns to the left, with the second to the right, and with the third it remains at rest. At 4 it turns once more to the left, at 5 to the right, at 6 it remains at rest, etc. It remained immovable only at the so-called trigonal numbers (3, 6, 9, 15, 21, etc.). Ritter tells us that when Campetti did not really count or did not think of the number, then it would not have any influence whatever upon the action of the instrument. This Ritter ascribes to the agency of electricity (which in the 18th and 19th centuries was made to play very much the same r?le that Satan had played in the 16th and 17th centuries).

The similarity of these two cases and that of Mr. Schillings is evident. When the questioner of the horse and the bearers of the "balancier" and of the divining rod are confident of success, they succeed. When they do not expect success, they fail.

[V] The French investigators Vaschide and Rousseau make a reference to this case, and mistakenly state the number of signals as 1500 instead of 115[30]. Ettlinger[31] takes over this wrong figure and makes the additional mistake of assuming that the reference is to an original investigation made by the two Frenchmen.

[W] All told, there are hardly more than half dozen experimental investigations of the color-sense in mammals,-to speak only of these. Three of them deserve especial mention. One, the work of the American, Kinnaman,[33] on two Rhesus monkeys. Then a brief but careful piece of work by Himstedt and Nagel.[34] These two investigators were able to determine that their trained poodle could distinguish red of any tone or shade from the other colors, and from Professor Nagel I learned that later the tests were extended and the same was shown to be true concerning the blue and the green. And finally there is an investigation which hitherto has been known only from a reference which Professor Dahl,[35] the investigator, himself makes. The work is on a monkey, Cercopithecus (Chlorocebus) griseoviridis Desm. (Professor Dahl has kindly allowed me to look over the records of the experiments. He intends to publish the monograph at an early date.)

All of these investigators arrive at the conclusion that the animals tested by them possess color-sense. The monkey last-mentioned shows one peculiarity: it was unable to distinguish a saturated blue from the black. It will require further tests to clear this up.

[X] There is no justification for the wide-spread belief that the horse which on account of the greater size of his eye (more correctly, on account of the greater focal distance) receives larger retinal images of objects than does the human eye, for that reason also sees objects, larger than we do. Horses' shying is often explained in this way. But the conclusion just mentioned is erroneous. The retinal image is not the perceptual image. It undergoes many transformations within the nervous system itself.

[Y] "Butzenscheiben" are the small circular panes of green glass, used in leaded windows in early days. They are high in the middle (hence the name: "Butze," a protuberance) with a number of concentric circles around the central elevation.-Translator.

[Z] Since no opportunity was given us to examine Hans's eyes we do not know what their condition is in this respect. Though it would have been interesting to know, it would hardly make any difference in the views presented. If Hans should prove to be either far or near-sighted, then, if we are to make any supposition at all, it would be that the defect could not be very great, since near sightedness exceeding 2 or 3 diopters and far-sightedness exceeding one diopter is seldom found in the case of the horse. According to Mr. von Osten, Hans at one time manifested a tendency to shy easily. Be this as it may, for little could be concluded from it, since in many extremely shy horses, no kind of visual imperfection can be discovered.

[AA] For the benefit of specialists I would say the following in addition to the more general remarks just made. For the most part, the determinations of refraction made on the eye of the horse are still rather unreliable. In sciascopy there is a dispute among investigators concerning ambiguous shadows, and in the use of the refraction-ophthalmoscope no definite region of the eye's background has been adhered to by the various investigators. It appears that Riegel, whose diligent researches mentioned on page 164 were published in 1904, knew nothing concerning the round area in the horse's eye, discovered by I. Zürn[42] in 1902. Also, if so great a degree of astigmatism is really the rule as is emphasized especially by Hirschberg[43] and Berlin,[44] then the simple refractive index usually given-sometimes within a half diopter-would be meaningless. Berlin[45] and Bayer[46] believe the vagueness of the retinal image resulting from the astigmatism, is offset by this: that the oval pupil functions as a stenopaic slit. In view of the width of the horse's pupil this appears to me to be rather hypothetical.

Concerning Berlin's theory of deflecting astigmatism I would say the following: Of the two ophthalmoscopic signs mentioned as being characteristic of this form of astigmatism,-the concentric circles and the arcuate deflection of the pathway of the fixated points,-when there is a movement of the eye of the observer (or of the eye observed), according to Berlin the former is not so constant as the latter. So far as I know, the concentric ring formation is mentioned only by Bayer[47] and Riegel,[48] and is said to occur principally in horses with myopic vision-and hence, relatively, in a minority of cases. Judging from the particulars, we are inclined to believe that a case of "Butzenscheiben"-lens reported by Schwendimann[48a] is in reality a case of senile sclerosis. Berlin repeatedly warns us against mistaking the one for the other.[48b] The arcuate deflection, on the other hand, has not been mentioned elsewhere as a personal observation. In Berlin's calculation[49] of the increase in the extent of the retinal pathway an ambiguity has crept in. He says that "in the astigmatic eye there are stimulated 207 times as many nervous elements as would be stimulated in the ideally normal eye." It ought to read "207 more" instead of "207 times as many." And this number holds only for the one case computed by Berlin, and under the specific assumption that exactly π/2 times the normal number of elements were stimulated (571 instead of 364). Therefore the general statement which Bayer[50] makes in his text-book, that according to Berlin's evaluation "207 times more nervous elements" are stimulated in the astigmatic eye than in the non-astigmatic one, does not hold true.

Closing this note, a few remarks concerning the experiments made by Dr. Simon and myself. All of the nine horses were tested for the vertical image by means of the ophthalmoscope. In most cases Wolff's electric speculum was used. Atropine was not employed.-For the laboratory tests the adipose and the muscular tissues were removed from the eye-ball and the rear part of the bulb cut away. The front part, containing the cornea and the lens, was fastened over one opening of a metal cylinder which was closed at the other end by means of a disc of ground glass. The whole, approximately as long as a horse's eye, was filled with a normal salt solution whose refractive index (1.336) corresponds quite closely with that of the vitreous humor of the horse's eye. The pressure from within was regulated so that on the one hand it was not dimmed and yet on the other there were no wrinkles in the cornea. The source of light-the filament of a Nernst lamp-was moved about in a plane 120 cm. distant from the eye and perpendicular to the optic axis. It was moved through the point of intersection as well as at various distances from it. Movement in horizontal and vertical directions was in each case along lines 150 centimeters in length, which would correspond to an angle of vision of not less than 64°. The pathway of the imaged point was controlled by means of the cross-hairs of the telescope. If in the same way we observe through the sclerotic of an intact eye-bulb a point of light falling upon the retina and shining through the sclerotic and choroid (which is not difficult when we use an intense light), then to the observer its pathway will, of course, appear to be deflected convexly toward the periphery,-and the deflection will appear the greater, the farther the point of light is removed from the optic axis.

[AB] K?nigsh?fer, who as we have already said, seconds the explanation given by the ophthalmologist Berlin (and who confounds "Butzenscheiben" astigmatism with the common, so-called regular form), believes[54] that not only astigmatism but also the shape of the blind-spot of the eye must be taken into consideration. This portion of the retina, where the fibres of the optic nerve enter the eye (and called "blind-spot" because there are no cells there that are sensitive to light) is very nearly circular in man, but differs in shape in the different species of animals. K?nigsh?fer thought he had discovered that a relatively elongated blind spot was favorable to keenness of vision. If we place the mammalia in series on the basis of their relative keenness of vision, he says, we would find that this series is identical with the one in which they are grouped with reference to the form of the blind-spot from the circular up to the most elongated. (In such a series the marmot takes the place of honor.)

This exposition is not very satisfactory, however. We cannot be sure what he means by "keenness of vision" ("scharf?ugigkeit"). Is it visual acuity in the usual sense of the term (as is said in one of his passages), or keenness in the perception of the movements of objects, (this would appear to be his real meaning), or both at the same time. But whatever the significance he may put into the term, any such attempt at grouping the lower forms must prove unsatisfactory from the very start on account of the scant data which we possess on visual perception in animals. The experiences of the hunt upon which K?nigsh?fer partly bases his view, are entirely inadequate for such a purpose. This much is certain, that the Osten horse, in spite of a blind-spot which, though somewhat oval, is by no means very elongated, possesses an extraordinary acuity in the perception of movements. Even if the parallelism mentioned by K?nigsh?fer were really shown to exist, it would not explain the matter until it were also shown in what way keenness of vision is dependent upon the shape of the blind-spot,-a portion of the eye which is not immediately operative in the visual sensation at all.

[AC] I can find examples of supposed suggestion in the case of animals given only by Rouhet.[61] He says that by means of suggestion he taught a half-year old half-blooded mare-colt which he had raised himself, to fetch and carry, and this in a very short time. In order to indicate to the colt what was wanted, Rouhet would concentrate with his whole mind upon the object intended (a watch), and at the same time he would bend forward slightly. In the third test, that is at the end of fifteen minutes, he had accomplished his purpose, and in the tenth lesson, no more mistakes occurred. The colt would fail to respond, however, as soon as he refrained from making any gestures, or was in a laissez faire frame of mind, or when he thought of other things. He therefore believes that there must have been some kind of immediate, though inexplicable, connection between the brain of the trainer and that of the horse. I think the explanation is evident: the connection was not as he thought, an immediate one, but arising through the mediation of the man's attitude ("attitude un peu baissée"), and of his movements ("gestes"), both resulting from his intense concentration ("tension de la pensée").

In general we may say that, no matter what content we may wish to put into the term "suggestion," not a single fact has since come to light which would justify, and much less demand, the application of the term to lower forms, unless we would expand the definition of the term to the extent of comprising every kind of command, every arousal of ideas, whatsoever. But it would then be nothing but a new name for old knowledge[62] and would lose all explanatory value. (Hypnotism, so-called, in the case of horses, I shall discuss elsewhere in another connection.)

[AD] An illustration is given by Babinet[66] concerning the horse of an English lord. Mr. Burkhardt-Foottit, also, that excellent trainer, who has been master for more than forty of the most highly-trained horses, tells us that while sitting on a well-managed horse it sometimes happened that he had merely thought of making a certain turn, when the horse immediately executed it, before he, the rider, had to his knowledge given any sign or aid. An observation belonging under this head is also made in Tolstoi's "Anna Karenina"[67], this perfect mine of acute psychological observation. In the famous description of the race we are told concerning Count Wronskij riding his Frou-Frou just behind Machotin mounted upon Gladiator, who was leading the race: "At the very moment when Wronskij thought that it was time to overtake Machotin, Frou-Frou, divining her master's thought, increased her pace considerably and this without any incitement on his part. She began to come nearer to Gladiator from the more favorable, the near side. But Machotin would not give it up. Wronskij was just considering that he might get past by making the larger circuit on the off-side, when Frou-Frou was already changing direction and began to pass Gladiator on that side." Similar experiences might be gathered elsewhere. Not infrequently the reflection of the rider that his horse had not for a long time indulged in some trick peculiar to him, will immediately call it forth; or doubts on the part of the rider concerning the possibility of crossing some barrier, are often the cause of the horse's fall or of his refusal to leap and of his running away.

[AE] All the authors who have given practical suggestions for the training of horses, whether free or with lunging reins, have great faith in the efficacy of calls, but usually recommend a mingling of calls and movements in the way of signs, (thus Loiset,[71] Baucher,[72] von Arnim[73]). It therefore cannot be stated just in how far the calls really effect anything. In other cases I am inclined to doubt outright the influence which is ascribed to the auditory signs. Meehan[74] gives an account of a horse that was exhibited in London in the early 90's of the last century. Pawing with his hoof, this horse apparently was able to count and answer questions in arithmetic, and among other accomplishments he was supposed also to be able to understand something of language. In reality, however, he merely responded to cues which were disclosed to the reporter by the trainer. In pawing, the horse was guided by movements of the trainer, and in nodding or shaking the head he reputedly got his cue from the inflections of the man's voice. Is it not probable that in this latter case it was the movements which accompanied speech that were alone effective in inducing the nod or the shake of the head, so that the exhibiter was deceiving not merely the public, but also himself? Perhaps we may also doubt the exposition made by the well-known hippologist, Colonel Spohr.[75] He tells us that it is easy to train horses to raise the left foot or the right foot in response to the commands "Left-foot!" or "Right-foot!" and that it will be the fore foot when one is standing in front of the horse, and the hind foot if one stands near the rear. It cannot be so very difficult, he thinks, even to get the horse to understand the commands "Left (or right)-fore foot!" and "Left (or right)-hind foot!"-and all without any other aids but the spoken words. Should this really be possible without even the slightest kind of designating movement?--The following case, again, I believe is undoubtedly based upon a misinterpretation. Redding[76] relates concerning his nineteen-year old horse that he himself had owned for thirteen years, and had always kept in single harness,--that this horse not only understood the meaning of a long list of words, such as: bureau, post-office, school, churchyard, apple, grass, etc., but he also knew a number of persons by name, as well as their places of residence. If he were told in advance to halt at a certain residence, he would do it without any further aid from the driver. For this reason the happy owner felt certain that the animal possessed a high order of intelligence and "that this horse does reason." What sources of error were here operative, whether signs were given by means of reins, or head or arm movements, could be determined only by a careful examination of the case.

And finally we would exercise some reserve in entertaining the suggestions for the acoustic education of horses which have come from various sources. Colonel Spohr[77] whom we have just been mentioning, thinks that it would not be a difficult matter to get a horse to respond with a walk to one smack of the lips, with a trot to two smacks, and with a galop to three, and then he could be made to slacken his pace once more into a trot in response to one long-drawn "Pst!" and to stop in response to two. Others have gone even further. Decroix,[78] at one time leader in veterinary affairs in France, conceived the idea of working out a universal language as regards the commands that are given to horses, in the humane purpose of sparing them the whip. He called it "Volapük hippique." For the commands "go," "right," "left," and "halt," he suggests these: "Hi!" "Ha!" "Hé!" and "Ho!" respectively. From these it was possible to make eight combinations, such as "Hi! Hi!" for "Trot!" "Hé! Hé!" for "Left about" (while the single "Hé" was to mean "Forward, to the left!") "Ho! Ho!" for "Back!" etc. Decroix thought that the whole system could be inculcated in a very few lessons. He even had a medal struck which was to be awarded to the driver or rider who should first exhibit a horse, thus instructed, to the Société Nationale d'Acclimatation de France (of which Decroix was president). Eight years have elapsed since then, but we have heard of no one who has earned the medal mentioned. In the future greater care will probably be exercised in the putting forth of such suggestions, and two sources of error may be guarded against, viz.: involuntary movements on the part of the rider or driver, and imitation of the horses amongst themselves. (One horse, guarded by an experienced rider, may serve as copy for ten others with inexperienced men in the saddle.)

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

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

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

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

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

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

P. 25 [229]. But even the most suitable questioners do not always succeed equally well ("les plus s?rs d'eux-mêmes ne réussissaient pas également tous les jours.")

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

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

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

P. 210 [93]. When there is too low a degree of tension, then too great a number will be tapped ("si votre volonté ne les [les tables] arrête pas au moment où se termine le chiffre pensé, elles continueront indéfiniment.")

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

P. 36 [151]. If the proper mood ("entrain habituel") is wanting and the tests are unsuccessful, it is best not to attempt some new and difficult experiment, but to turn to some that are simpler and more entertaining ("La table obéissait mal; les coups étaient frappés mollement et comme à regret.... Alors nous avons pris un parti dont nous nous sommes bien trouvés; nous avons persévéré, et persévéré gaiement; ... nous avons écarté la pensée des tentatives nouvelles, et insisté sur les opérations aisées et amusantes. Après un certain temps les dispositions étaient changées, la table bondissait et attendait à peine nos commandements.")

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

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

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

P. 28, 29, 217 [72]. When of two experimenters each tries to get the horse to tap a different number, then that one who is the better able to compel the animal's attention, will be the successful one. ("L'un veut faire prévaloire un chiffre pensé plus considérable, l'autre un chiffre pensé moins considérable.... Eh bien: l'opérateur le plus puissant l'emporte." "Ainsi A est chargé secrètement de faire frapper 25 coups, B est chargé secrètement de l'arrêter à 18; A l'emporte, et les 25 coups s'achèvent.... On fait maintenant l'inverse: B est chargé secrètement de faire frapper 13 coups; A est chargé secrètement de l'arrêter à 7; A l'emporte encore et le chiffre 7 ne peut être dépassé.")

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