Book excerpt: To those who will only believe in phenomena which are reproducible at will, it is easy to answer them: you do not manufacture comets, meteorites, magnetic disturbances due to sunspots, and yet you observe them. Metapsychical phenomena are registered in the records of Occultism. That is all. The only thing to do is to check them. But the right remains to unite them amongst themselves by an attempt at a general explanation. The study of the Invisible, of the forces which it conceals, of the human fluids, is yet but at its dawn. Patience ! To deny is absurd. To observe is scientific. To think is wise. This is what I have done. It is what you will do after having read this book, the well arranged summing up of vast reading and lengthy thought.