It is impossible to reply categorically to this question because it is not possible, and never will be, to have a scientific proof of the identity of the beings who manifest themselves. The fact that I hear, that I see, that I touch a phantom; that I recognize in it the form and the attitude of persons whom I have known and whom the medium has neither known nor of whom she has even heard the names; that I have the most lively and affecting testimony to the presence of this ephemeral apparition,--all that will not be sufficient to constitute the scientific fact which none can refute, and which shall be worthy to remain in the annals of science along with the experiments of Torricelli, Archimedes and Galvani. It will always be possible to imagine an unknown mechanism by the aid of which elemental substance and power may be drawn from the medium and the sitters and combined in such a way as to produce the indicated effects. It will always be possible to find in the special aptitudes of the medium, in the thought of the sitters, and even in their attitude of expectant attention, the cause of the _human_ origin of the phenomena. It will always be possible to unearth from the arsenal of the attacks made upon these studies during the last fifty years, some generic or specific argument, either _ad rem_ or _ad hominem_, while ignoring or feigning to ignore the refutation of the argument which has already been made. The question, then, reduces itself at once to an individual study of cases either directly observed or obtained from some sure hand, in order on the one hand, to create a personal conviction capable of resisting the scathing ridicule of the sceptics, and, on the other hand, to prepare public opinion to admit the truth of cases observed by persons worthy of credence. With regard to the first of these, the illustrious experimenter Sidgwick, has already said that no fact or case exists capable of convincing everybody, but that each one, by patiently and calmly observing, may find such fact or case as will suffice to establish his own conviction. I may say that for myself such a case exists. I need only refer to the phenomena in which I have personally participated in the seances with Eusapia. With regard to the second point I could say much, but that would lead me beyond the subject matter and the limits of this study.