EINSTEIN: One might almost suppose that your genuine Henry Slade served as a model for them.
M.: For certain reasons I regard this as out of the question, mainly because the true Slade gave "demonstrations" only occasionally, his chief object being to interest scientists. He, himself, repeatedly asserted that he did not understand his own achievements, and he unceasingly requested the supervision of professional physicists and physiologists, to whom the unusual phases in his nature were to serve as objects of study. The result was that people like Dubois-Reymond, Helmholtz, and Virchow refused to see him, not to mention experiment with him.
EINSTEIN: These men cannot be reproached for acting in this way. Slade was regarded as a representative of a four-dimensional world in the spiritistic sense; serious scientists must avoid all humbug of this sort, since even slight interest in it can easily be misinterpreted by the ignorant public.
M.: Not every one was afraid of compromising himself. After closed doors had greeted Slade in Berlin, he went to Leipzig, where he became an object of study for one important scientist.
EINSTEIN: You are referring to Friedrich Zöllner, who undoubtedly had a reputation as an astrophysicist to preserve. But he would have served his reputation better if he had not entered into this adventure with the American spiritist.
M.: Perhaps there will some day be cause for a revision of opinion on this point. The documents are extant, even if, half forgotten, they are reposing in various libraries. A renewed investigation of Zöllners Scientific Dissertations, dating from 1878 to 1891, might lead to the judgment that his ghostly interpretations are to be regarded as occult in the worst sense, and yet one would marvel that a great scientist, such as he was, should have felt himself at a complete loss with his knowledge, so that he was forced to resort to abstruse methods in order to escape from the mental confusion into which Slade had plunged him.
EINSTEIN: That merely shows that Slade, as a cunning practician, surpassed him, and that Zöllner did not succeed in seeing through his machinations.
M.: This would lead one to assume that Slade knew more physics than the Leipzig professor. For in a great number of experiments Zöllner himself had prescribed the conditions, including all contrivances which made deception so much the more unlikely, since Slade himself could not know what Zöllner's intentions were. It was a question of Electricity, Magnetism, Optics including prepared conditions of polarization, involved Mechanics, in short, things that Zöllner as a professional physicist understood thoroughly, and which, moreover, were controlled by others of his profession. Among the latter was the celebrated professor of Electricity, Wilhelm Weber, who, like Zöllner, found himself faced by phenomena that were utterly incomprehensible to him. It would be a profitable undertaking to bring these dissertations to light again, and it would easily be recognized that the things described actually deal with scientific problems and have not the remotest connexion with tricks of magic. For example, there is an account of an incredible anatomical feat. On flour which had been placed carefully in a dish beforehand, there suddenly appeared the imprint of a naked human foot, whilst Slade was present at a certain distance, being fully clothed and subject to careful scrutiny. The footprint showed all the surface-details of the skin, as was confirmed by authorities, just as only a left foot could produce them, but not an artificial copy.
EINSTEIN: And from this Zöllner inferred the intervention of supernatural beings? He would have done better to measure the dimensions of the foot.
M.: So he did—at once. A difference of four centimetres between the length of Slade's foot and the copy was disclosed. This riddle, like so many others, remained unexplained. I must repeat that I am not in the slightest degree disposed to assert that occult phenomena really occur, but am interested only in seeing that they are investigated carefully by qualified persons.