Several years ago I designated this unknown force by the title _psychical_. This designation may well be retained. Can we not find the happy medium between absolute negation and dangerous credulity? Is it reasonable either to deny everything we do not comprehend, or to accept all the fantasies engendered in the vortex of disordered imaginations? Can we not achieve at the same time the humility which becomes the weak and the dignity which befits the strong? I conclude this statement as I began it, by declaring that it is not in favor of the Davenport Brothers that I plead; nor do I take up the gauntlet for any sect, for any group of people, or for any person whatsoever; but I contend in behalf of certain facts, of whose validity I was convinced years ago, though without understanding their cause. I beg the reader to excuse the length of this citation; but it seems to me to serve so naturally as an introduction to this present inquiry that even to-day, after a lapse of a quarter-century, I really see no important changes to be made in this old declaration, except to add that it now appears to me to have been rather audacious on the part of a man so very young, and that it forthwith won him many hearty enemies among the elect of science. The experimental method is bound to conquer here, as everywhere. Let us, then, without partisanship, study the question under its divers aspects. 1 "The immortality of the soul is a matter so important," writes Pascal, "that one must have lost all moral sensibility if he remains indifferent as to its nature." Why should we give up the hope of ever arriving at a knowledge of the nature of the thinking principle which animates us, and of ascertaining whether or not it outlives the destruction of the body? It must be admitted that hitherto science has taught us nothing on this fundamental subject. Is this any reason for renouncing the study of the problem? On this, as on many other points, we are not of the same mind as those material Positivists who declare themselves satisfied with not knowing anything. We think, on the contrary, that we should attack the problem by all methods, and not neglect a single hint which may aid the solution.