It may not be superfluous to caution the reader that the word "medium" is employed in these pages without any preconceived idea, and not in the etymological sense in which it took its rise at the time of the first Spiritualistic theories, which affirmed that the man or the woman endowed with psychic powers is an inter_mediary_ between spirits and those who are experimenting. The person who has the power of causing objects to move contrary to the laws of gravity (even sometimes without touching them), of causing sounds to be heard at a distance and without any exertion of muscular force, and of bringing before the eyes various apparitions, has not necessarily, on that account, any bond of union with disembodied minds or souls. We shall keep this word "medium," however, now so long in use. We are concerned here only with facts. I hope to convince the reader that these things really exist, and are neither illusions nor farces, nor feats of prestidigitation. My object is to prove their reality with absolute certainty, to do for them what (in my volume _The Unknown and the Psychic Problems_) I have done for telepathy, the apparitions of the dying, premonitory dreams, and clairvoyance. I shall begin, I repeat, with experiments which I have recently renewed; namely, during four seances on March 29, April 5, May 30, and June 7, of 1906. 1. Take the case of the levitation of a round table. I have so often seen a rather heavy table lifted to a height of eight, twelve, sixteen inches from the floor, and I have taken such undeniably authentic photographs of these; I have so often proved to myself that the suspension of this article of furniture by the imposition _upon it_ of the hands of four or five persons produces the effect of a floating in a tub full of water or other elastic fluid, that, for me, the levitation of objects is no more doubtful than that of a pair of scissors lifted by the aid of a magnet. But one evening when I was almost alone with Eusapia, March 29, 1906 (there were four of us altogether), being desirous of examining at leisure how the thing was done, I asked her to place her hands with mine upon the table, the other persons remaining at a distance. The table very soon rose to a height of fifteen or twenty inches _while we were both standing_. At the moment of the production of the phenomenon the medium placed one of her hands on one of mine, which she pressed energetically, our two other hands resting side by side. Moreover, on her part, as on mine, there was an act of will expressed in words of command addressed to "the spirit": "Come now! Lift the table! Take courage! Come! Try now!" etc. We ascertained at once that there were two elements or constituents present. On the one hand, the experimenters address an invisible entity. On the other hand, the medium experiences a nervous and muscular fatigue, and her weight increases in proportion to that of the object lifted (but not in exact proportion).