reputation, believed that the case was one worthy of careful investigation.

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

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

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

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

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

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

In truth he probably was neither, but I was brief in my report, for otherwise I would have been obliged to go into more detail than the case warranted. And a judgment passed upon a human personality is quite a different matter from a judgment upon a horse. If it is unscientific to make unqualified statements concerning a horse after the performance of only a few experimental tests, it is certainly an unwarranted thing to pass a moral judgment upon a man upon the basis of meagre material. Anyone who would assume the rôle of judge should bear in mind that here too we have more than a hundredfold the material which they could bring forward, and among it some which, if taken alone, would be more unfavorable than any that they had. But here all things should be weighed together, and not in isolation. A former instructor of mathematics in a German gymnasium, a passionate horseman and hunter, extremely patient and at the same time