When we consecrate our lives to an idea, useful, noble, exalted, we should not hesitate for a moment to sacrifice personalities; above all, our own self, our interest, our self-esteem, our natural vanity. This sacrifice is a criterion by which I have estimated a good many characters. How many men, how many women, put their miserable little personality above everything else! If the forces of which we are to treat are real, they cannot but be natural forces. We ought to admit, as an absolute principle, that everything is in nature, even God himself, as I have shown in another work. Before any attempt at theory, the first thing to do is to scientifically establish the real existence of these forces. Mediumistic experiences might form (and doubtless soon will form) a chapter in physics. Only it is a kind of transcendental physics which touches on life and thought, and the forces in play are pre-eminently living forces, psychic forces. I shall relate in the following chapter the experiments I made between the years 1861 and 1865, previous to the penning of the protest, reprinted in the long citation above given (in the Introduction). But, since in certain respects they are summed up in those I have just had, in 1906, I will begin by describing the latter in this first chapter. In fact, I have recently renewed these investigations with a celebrated medium,--Mme. Eusapia Paladino, of Naples, who has been several times in Paris; namely, in 1898, 1905, and, very recently, in 1906. The things I am going to speak of happened in the salon of my home in Paris,--the last ones in full light without any preparation, very simply, as if during after-dinner talks. Let me add that this medium came to Paris during the first months of the year, 1906, at the invitation of the Psychological Institute, several members of which have been recently engaged in researches begun long ago. Among these savants I will mention the name of the lamented Pierre Curie, the eminent chemist, with whom I had a conversation a few days before his unfortunate and terrible death. My mediumistic experiences with Mme. Paladino formed for him a new chapter in the great book of nature, and he also was convinced that there exist hidden forces to the investigation of which it is not unscientific to consecrate one's self. His subtle and penetrating genius would perhaps have quickly determined the character of these forces. Those who have given some little attention to these psychological studies are acquainted with the powers of Mme. Paladino. The published works of Count de Rochas, of Professor Richet, of Dr. Dariex, of M. G. de Fontenay, and notably the _Annales des sciences psychiques_, have pointed them out and described them in such detail that it would be superfluous to recur to them at this point. Farther on we shall find a place for discussing them.