the rule that during tests in which the method is that of procedure without knowledge the solutions should be known to no one of those present. Finally the tests made by the September-Commission and reported in Supplement III (page 255) may possibly belong under this head. Since they were not followed out any further, I am unable to render a definite judgment upon them. In most of these tests the question itself, as put by Mr. von Osten, was not adequately answered, but curiously enough, however, the number which had been given to Hans in von Osten's absence and which formed the initial number of some mathematical operation, was tapped correctly. This may possibly be explained by the assumption that this initial number had been retained in the memory of some of those present, (see page 149, on the "perseverative tendency"), and that the horse, since he had been working with some of them, responded to one of those present. Chance may have played some part also. [Footnote L: Mr. Schillings, however, did succeed in making a number of tests with the co-operation of others who had never before worked with the horse. These tests were made under the following conditions: The horse was standing in his stall, when Mr. Schillings and another gentleman approached him. There was no one else present. Mr. Schillings, who tried to remain as passive inwardly, as possible, asked his partner to think consecutively of different numbers between one and 20, which thus were known to him alone. Hans was then commanded by Mr. Schillings to tap the numbers, which he did, to the great astonishment of the men, and especially of Mr. Schillings. In like manner Mr. Sander, a staff physician in the marine, received--so he writes me--three correct responses to four questions which he put to the horse. It happened also in the case of two scientific men and finally, too, in my own case when I first came in contact with the horse, (see page 88). The horse's reaction was brought about in the same way in every one of these instances. Mr. Schillings, in bending forward slightly, thereby started the horse a-tapping, and his companion--just as innocently--interrupted the process by means of a movement of his head, when the right number of taps was reached.