I have read with much attention all that the late Professor Zoellner has written on this subject. His explanation has a purely material basis,--that is to say, it is the hypothesis of the objective existence of a fourth dimension of space, an existence which cannot be comprised within the scope of our intuition, but the possibility of which cannot be denied on that ground alone. Once grant the reality of the experiments which he describes, and it is evident that his theory of these things is the most ingenious and probable that can be imagined. According to this theory, mediumistic phenomena would lose their mystic or mystifying character and would pass into the domain of ordinary physics and of physiology. They would lead to a very considerable extension of the sciences, an extension such that their author would deserve to be placed side by side with Galileo and Newton. Unfortunately, these experiences of Zoellner were made with a medium of poor reputation. It is not only the sceptics who doubt the good faith of M. Slade: it is the Spiritualists themselves. M. Aksakof, whose authority is very great in similar matters, told me himself that he had detected him in trickery. You see by this that these theories of Zoellner lose any support they might have derived from the exact demonstration of experiment, at the same time that they remain very beautiful, very ingenious, and quite possible. Yes, quite possible in spite of everything; in spite of the lack of success that I had when I tried to reproduce them with Eusapia. On the day when we shall be enabled to make, with absolute sincerity, _a single one_ of these experiments, the matter will have made great progress; from the hands of charlatans it will have passed into those of physicists and physiologists. Such is the communication made to me by M. Schiaparelli. I found his reasoning to be without defect, and it was in a state of mind entirely analogous to his that I arrived at Monfort-l'Amaury (with all the more interest because Slade was one of the mediums of whom I was just now speaking).